Chapter 1: Air Quality and Climate
We must take the lead in addressing the challenge of global warming
that could make our planet and its climate less hospitable and
more hostile to human life. Today, I reaffirm my personal and
announce our nation's commitment to reducing our emissions of
greenhouse gases to their 1990 levels by the year 2000. I am instructing
my administration to produce a cost-effective plan that can continue
the trend of reduced emissions. This must be a clarion call, not
for more bureaucracy or regulation or unnecessary costs, for American
ingenuity and creativity, to produce the best and most energy-efficient
technology.
President Bill Clinton
The composition of the atmosphere is a primary determinant of
global temperature and climate. In turn temperature and climate
establish conditions and limitations for life on earth. There
was a time, not long ago, when air quality and climate would not
have been included in the same chapter. Today, however, evidence
strongly suggests that pollutants emitted into the air from anthropogenic
(human-made) sources have the potential to change the climate
of the planet.
The good news is that, between 1983 and 1992, auto emissions were
down because of pollution control; the bad news is that Americans
are driving more miles each year. The nation cannot afford to
rest on its air quality laurels.
As a world leader in air pollution control, the United States
continues to work toward air quality goals using advanced technologies
and innovative policies such as market-based regulation. The Clean
Air Act Amendments of 1990 called for achieving air quality goals
in a more flexible, cost-effective, market-based manner than had
been the case in prior years. These amendments, now in early stages
of implementation, will have their major impact in the coming
years. Meanwhile in some parts of the nation, exceedances of health-based
national ambient air quality standards (NAAQS) set by the U.S.
Environmental Protection Agency (EPA) continue to pose risks to
human health and the environment.
The technology that has improved the emission rates of new automobiles
is contributing to improvements in air quality. For example 1990-model
vehicles emit hydrocarbons and carbon monoxide at only one-third
the rate of 1975-model vehicles. In the near future, the nation
can expect further reductions in emissions as older vehicles are
retired and replaced by newer, cleaner ones. Even with these technological
improvements, however, the total vehicle emissions could once
again increase if vehicle miles of travel continue to rise.
Various trends are contributing to the continued rise in vehicle
miles of travel:
. Increase in the number of workers,
. Increase in vehicle ownership,
. Decrease in vehicle occupancy rate,
. Decrease in use of public transportation,
. Longer average trip length,
. Growth in suburb-to-suburb travel, and
. Low per-mile driving costs.
The real cost of gasoline, for example, is now lower than it was
in 1950. Efforts to reduce travel in single-occupant vehicles
and total vehicle miles of travel face difficult challenges in
light of these trends.
Over the past decade, air quality levels in the United States
have shown continued improvement. The six pollutants for which
the EPA sets NAAQS are carbon monoxide, lead, nitrogen dioxide,
ozone, particulates, and sulfur dioxide. Levels tracked by monitoring
stations document progress in reducing air levels for each pollutant.
Carbon monoxide (CO) is a colorless, odorless, and poisonous gas
produced by the incomplete burning of carbon in fuels. Elevated
carbon monoxide levels can enter the human bloodstream and reduce
normal delivery of oxygen to organs and tissues. In areas where
levels exceed the NAAQS, the health threat is most serious for
persons who suffer from cardiovascular disease, particularly those
with angina or peripheral vascular disease, although healthy individuals
also can be affected. Such exposure is associated with impairment
of visual perception, manual dexterity, learning ability, and
performance of complex tasks.
Two-thirds of the nationwide emissions of carbon monoxide are
from transportation sources, with the largest contribution coming
from highway motor vehicles (such as light-duty gas vehicles and
motorcycles, light-duty and heavy-duty gas trucks, and diesels).
Long-term trends indicate that emissions for all types of highway
vehicles nearly tripled from 1940 through 1970. From 1970 to 1980,
emissions from highway vehicles increased only 11 percent, largely
because the nation implemented the Federal Motor Vehicle Control
Program that regulates emissions from new vehicles. This program
has resulted in widespread use of catalytic converters on automobiles
to reduce carbon monoxide, nitrogen oxides, and volatile organic
compound emissions. Another result has been the use of unleaded
gasoline for vehicles with these converters. Since 1980 carbon
monoxide emissions have decreased 37 percent as a result of pollution
control and retirement of older vehicles without converters.
Ambient atmospheric concentrations of carbon monoxide have recorded
a general long-term improvement. The 10-year period, 1983-1992,
showed a 34-percent improvement, which agrees with the estimated
30-percent reduction in highway vehicle emissions. These reductions,
largely attributable to vehicle emission controls, occurred despite
a 37-percent increase in vehicle miles of travel in the United
States during the reporting period. The environmental and transportation
communities are concerned that rising vehicle miles of travel
could overtake the emission improvements realized over the last
decade.
Despite these improvements the EPA designated 42 areas as nonattainment
for carbon monoxide in November 1993. These areas failed to meet
the carbon monoxide NAAQS of 9 ppm in an 8-hour period. Based
upon the magnitude of carbon monoxide concentrations, 41 areas
were classified as moderate, with Los Angeles alone classified
as serious.
Prior to 1993 the EPA had designated Syracuse, New York, as moderate
nonattainment for carbon monoxide; Knoxville, Tennessee, as marginal
nonattainment for ozone; and Greensboro, North Carolina, as moderate
nonattainment for ozone. The EPA, in 1993, was able to redesignate
these areas as attainment.
First the EPA Administrator had to determine that the areas had
attained the national ambient air quality standard and that the
improvement in air quality was the result of permanent and enforceable
reductions in emissions. In addition other NAAQS criteria had
to be met. Each area was required to have an approved applicable
implementation plan describing the measures used to reduce emissions
and achieve attainment and a maintenance plan showing that the
ambient air standard would be maintained for at least ten years
after redesignation. These plans are designed for a particular
area but draw on national guidance concerning applicable controls
for certain types of pollution sources.
Syracuse helped achieve attainment with the carbon monoxide standard
through a combination of measures including a traffic management
plan for major events in the downtown area (such as concerts and
athletic events) and institution of a ride-share program. Knoxville
applied reasonably available control technology (RACT) to major
emission sources in its efforts to attain the ozone standard.
Greensboro, in addition to applying RACT for major sources, adopted
an inspection/maintenance (I/M) program in two counties in the
nonattainment area.
In September 1993 Syracuse became the first area in the nation
to be redesignated by the EPA as attainment.
The major sources of atmospheric lead emissions are lead gasoline
additives, nonferrous smelters, and battery plants. Transportation
contributes more emissions than any other sector of the U.S. economy.
Exposure to lead can occur through multiple pathways, including
inhalation of air and ingestion of lead in food, water, soil,
or dust. Lead accumulates in the body in blood, bone, and soft
tissue. Because it is not readily excreted, lead also affects
the kidneys, nervous system, and blood-forming organs. Exposure
in adults to lead levels exceeding the NAAQS can cause seizures,
mental retardation, and behavioral disorders. Fetuses, infants,
and children are most susceptible to lead, which can cause central
nervous system damage; however, individuals as well. Studies show
that lead may be a factor in high blood pressure and subsequent
heart disease in middle-aged white males.
Lead emissions from highway sources decreased sharply from 1970
to 1986 as a result of the Federal Motor Vehicle Control Program.
Gasoline consumption increased 16 percent between 1970 and 1975,
but because of the reduced lead content of gasoline, lead emissions
from highway vehicles actually decreased 24 percent. Since 1984
lead emissions from transportation sources have decreased 96 percent,
brought about by increased use of unleaded gasoline in catalyst-equipped
cars, which made up 99 percent of the gasoline market in 1993.
In 1984, the unleaded share of the gasoline market was about 60
percent. In addition to the use of unleaded gasoline, the decrease
can be attributed to the reduced lead content in leaded gasoline,
which went from an average of 1.0 gram per gallon to 0.1 grams
per gallon in January 1986.
Programs are also in place to control lead emissions from stationary
sources. Lead emissions from fuel combustion by industry and
lead smelters, which contribute to total lead emissions, have
decreased over the past two decades. The reductions reflect utility
and industrial lead-emission controls and some plant closures.
Ambient lead concentrations in urban areas, where most lead- monitoring
stations are located, decreased 89 percent since 1984. This improvement
has been evenly distributed over the entire network of 204 monitoring
sites. Over the past decade, ambient lead concentrations at 66
monitoring sites near such industrial sources of lead as smelters
and battery plants improved 63 percent. Most areas in the United
States meet national air quality standards for lead. Those that
do not are industrial areas impacted by point sources of lead.
In 1993 these areas were Cleveland, Ohio; Indianapolis, Indiana;
Memphis, Tennessee, and parts of Alabama and Mississippi; Omaha,
Nebraska, and parts of Iowa; Philadelphia, Pennsylvania, and parts
of New Jersey; and St. Louis, Missouri, and parts of Illinois.
Nitrogen dioxide is a yellowish brown, highly reactive gas present
in the urban atmosphere. Formed by the oxidation of nitrous oxide,
it is emitted when fuels burn at high temperatures. Nitrogen dioxide
plays a major role, together with volatile organic compounds,
in the atmospheric reactions that produce harmful, ground level
ozone. It is also a precursor to acidic deposition and contributes
to environmental nitrogen loading that can affect both aquatic
and terrestrial ecosystems.
Nitrogen dioxide can irritate the lungs, cause bronchitis and
pneumonia, and lower resistance to respiratory infections such
as influenza. Continued or frequent exposure to concentrations
exceeding the NAAQS can cause pulmonary edema.
The two main sources of nitrogen dioxide are transportation and
stationary fuel combustion from electric utilities and industrial
boilers. Emissions from all sources have increased since the turn
of the century. Since 1984 reductions have occurred in emissions
from many sources, although total 1993 emissions were 1 percent
higher than 1984 figures. Fuel combustion emissions have remained
relatively constant during the last five years. Most decreases
in mobile-source emissions occurred in urban areas. The Federal
Motor Vehicle Control Program and the New Source Performance Standards
recently set by the EPA have helped reduce the growth of nitrogen
dioxide emissions from electric utilities and highway sources.
Ambient concentrations of nitrogen dioxide increased significantly
during the first two-thirds of the century as a result of increased
fuel consumption. Since 1984, however, concentrations have declined
by 12 percent. Los Angeles, the only urban area in the past ten
years with recorded violations of the annual average nitrogen
dioxide standard, in 1992 for the first time had air quality levels
that met this standard and continued to improve in 1993.
Trospheric (Ground-level) ozone is a major component of smog.
While ozone in the upper atmosphere (stratosphere) benefits life
by shielding the earth from harmful ultraviolet radiation from
the sun, concentrations of ozone at ground level in excess of
the NAAQS are a major health and environmental concern. Ozone
is not emitted directly into the atmosphere but is formed through
complex chemical reactions between precursor emissions of volatile
organic compounds and nitrogen oxides in the presence of sunlight.
These reactions are stimulated by light intensity and temperature
so that peak ozone levels occur typically during the warmer times
of the year, especially under dry, stagnant conditions.
The reactivity of ozone causes health problems because it damages
lung tissue, reduces lung function, and sensitizes the lungs to
other irritants. Ambient levels of ozone not only affect persons
with impaired respiratory systems but healthy adults and children
as well. Several hours of exposure to ozone in doses that exceed
the NAAQS can reduce lung function in normal, healthy people during
exercise. This decrease in lung function generally is accompanied
by symptoms including chest pain, sneezing, and pulmonary congestion.
Ozone also can damage forests and crops.
Transportation and industrial sources emit volatile organic compounds
(VOCs) and nitrogen dioxide, which are the precursor chemicals
of ozone. Emissions of VOCs from fuel combustion have declined
steadily since 1900, with the exception of a recent peak caused
by residential wood combustion. Emissions from industrial processes
increased from 1900 to 1970, but emission control devices and
process changes have helped limit these increases. Decreases in
emissions after 1970 are also attributed to the substitution of
water-based emulsified asphalt for asphalt liquefied with petroleum
distillates.
Emissions from transportation sources increased from 1900 to 1970,
first from railroads and later from highway vehicles. By 1970
railroads were contributing only 1 percent of total emissions,
while highway emissions had risen to 41 percent. Since then highway
emissions from diesel and gasoline-powered vehicles have declined
by 50 percent from the 1970 level as a result of the Federal Motor
Vehicle Control Program and national limits on fuel volatility.
Overall total emissions of VOCs are estimated to have declined
by 9 percent since 1984.
Ambient concentrations of ozone improved nationally by 12 percent
from 1983 to 1992. The 1993 composite average is higher than the
1992 level, but it is noteworthy that 1992 ozone levels were the
lowest of the past ten years. Since 1984 the expected number of
exceedances of the ozone NAAQS also has decreased by 60 percent.
Air pollutants called particulates include dust, dirt, soot, smoke,
and liquid droplets. Particulates are emitted directly into the
air by sources such as factories, power plants, cars, construction
activity, fires, and natural windblown dust. Particles also form
in the atmosphere from the condensation or transformation of emitted
gases such as sulfur dioxide and volatile organic compounds.
The major effects on human health from concentrations of particulates
that exceed the NAAQS often are associated with sulfur dioxide.
They include breathing and respiratory symptoms, aggravation of
existing respiratory and cardiovascular disease, alterations in
the body's defense systems against foreign materials, damage to
lung tissues, carcinogenesis, and premature mortality. Individuals
with chronic obstructive pulmonary or cardiovascular disease,
influenza, or asthma as well as children and the elderly are most
likely to be sensitive to the effects of particulates. Particulate
matter also soils and damages building materials and impairs visibility
in many parts of the country.
In 1987 the EPA promulgated annual and 24-hour standards for particulate
matter, using a new indicator, PM-10, which includes only those
particles with aerodynamic diameter smaller than ten micrometers.
These smaller particles are more likely to be responsible for
adverse health affects because of their ability to reach the lower
thoracic region of the respiratory tract. The new standards specify
an expected annual arithmetic mean not to exceed 50 micrograms
per cubic meter. They also specify that expected 24-hour concentrations
greater than 150 micrograms per cubic meter per year may not exceed
one occurrence per year.
PM-10 particulates are emitted by point and nonpoint sources:
. Point Sources. These include fuel combustion by electric utilities
and industry; industrial processes involving chemicals, metals,
and petroleum; and transportation.
. Nonpoint Sources. Among these are fugitive dust from agriculture,
construction, mining, quarrying, paved and unpaved roads, and
wind erosion.
Over the 9-year period, 1985-1993, total PM-10 emissions from
point sources decreased almost 3 percent. PM-10 emissions by highway
vehicles and off-highway vehicles decreased by 7 percent between
1985 and 1993, while emissions from a category entitled, Fuel
Combustion, decreased 14 percent. Emissions in this category are
produced predominantly by residential wood combustion'-the in-home
use of fireplaces and woodstoves. Several innovative approaches
to controlling residential wood combustion are responsible for
the large decrease in this emission category.
Fugitive dust contributes six to eight times more PM-10 particulates
than point sources; it is consistently emitted by construction
activity and unpaved roads. Among road types, emissions from unpaved
roads have remained fairly steady, while emissions from paved
roads are estimated to have increased 30 percent since 1985, most
likely due to increased vehicle traffic. Emissions from construction
sites have decreased an estimated 13 percent since 1985. Mining
and quarrying, sources estimated to be a relatively small contributor
to total fugitive particulate matter emissions at the national
level, can be major factors in local areas.
A minor contributor to the national total, agricultural tilling
is a major source of particulates in specific regions of the country,
such as the Great Lakes, Upper Midwest, and Pacific Northwest.
Over the 9-year period, 1985-1993, fugitive dust emissions showed
no significant change in these areas. PM-10 emissions caused by
wind erosion are very sensitive to regional soil conditions and
year-to-year changes in total precipitation. Accordingly estimated
emissions from wind erosion were extremely high for the drought
year of 1988.
Measured ambient air PM-10 concentrations decreased by 20 percent
between 1988 and 1993. Declines in particulate levels are attributable
to the installation of pollution control devices in electric utilities
and to reduced activity in some industrial sectors, such as iron
and steel.
Ambient sulfur dioxide results largely from stationary source
coal and oil combustion, steel mills, refineries, pulp and paper
mills, and from nonferrous smelters. The largest and most consistent
source of these emissions has been coal-burning electric power
plants.
Human exposure to concentrations of sulfur dioxide exceeding the
NAAQS can affect breathing and aggravate existing respiratory
and cardiovascular disease. Sensitive populations include asthmatics,
individuals with bronchitis or emphysema, children, and the elderly.
Sulfur dioxide is a primary contributor to acidic deposition (acid
rain), causing acidification of lakes and streams and damaging
trees, crops, historic structures, and statues. In addition sulfur
compounds in the air contribute to visibility degradation in large
parts of the country, including some national parks. The conversion
of sulfur dioxide to sulfate aerosols in the atmosphere could
impact global climate change.
Historic emissions of sulfur dioxide from fuel combustion and
industrial processes increased steadily from 1900 until 1925 and
then decreased during the 1930s primarily because of the Great
Depression, only to increase sharply from 1940 to 1970. During
the 1970s and early 1980s, emissions decreased by 25 percent as
the result of several factors:
. Coal cleaning and lower sulfur coal blending by electric utilities;
. Reduction in coal burning by industrial, commercial, and residential
consumers;
. Increased use of emission control devices by industry, especially
sulfuric acid manufacturing plants; and
. Byproduct recovery of sulfuric acid at nonferrous smelters.
Emissions have declined slightly in recent years. Nationally the
long-term trend in ambient sulfur dioxide concentration shows
a 26-percent reduction over the 10-year period, 1984-1993, although
the annual rate of decline has slowed over the last few years.
Currently there are 47 areas in the United States do not meet
national air quality standards for sulfur dioxide.
Although ambient air quality improvements in the 1984-1993 period
are encouraging, population estimates suggest that 59 million
people live in counties where pollution levels failed to meet
one or more air quality standards in 1993. Such estimates provide
a relative measure of the extent of the problem for each pollutant.
As an indicator, however, they have limitations. For example,
an individual living in a county that violates an air quality
standard may not actually be exposed to unhealthy air.
Urban, ground-level ozone (smog) continued to be the most pervasive
air quality problem, with an estimated 44.6 million people living
in counties that did not meet the ozone standard. This figure,
however, the lowest for the 10-year period, represents a substantial
decrease compared to the 112 million people thought to live in
areas that did not meet ozone NAAQS in 1988 when hotter, drier
meteorological conditions prevailed and contributed to more ozone
formation. The decrease is also partly because of new emission
control programs.
The EPA developed the Pollution Standards Index (PSI) as an air
quality indicator for describing urban air trends. The PSI has
found widespread use in the air pollution field for reporting
daily air quality to the general public. The index integrates
information from many pollutants across an entire monitoring network
into a single number that represents the worst daily air quality
experienced in an urban area. It is computed for carbon monoxide,
nitrogen dioxide, ozone, particulates (PM-10), and sulfur dioxide.
The index is based on short-term National Ambient Air Quality
Standards (NAAQS), Federal Episode Criteria, and Significant Harm
Levels.
Index Range Health Effects Categories
0 to 50 Good
51 to 100 Moderate
101 to 199 Unhealthful
200 to 299 Very Unhealthful
300 and Above Hazardous
The impact of hot dry summers in 1983 and 1988 in the eastern
United States can be measured by examining total PSI data along
with PSI data for selected metropolitan areas. Pittsburgh is the
only city where a significant number of PSI days greater than
100 are caused by pollutants other than carbon monoxide or ozone;
the Pittsburgh pollutants are sulfur dioxide and PM-10 particulates.
The year 1992 marked the first time since the EPA began making
population estimates that the agency recorded no monitoring violations
of either sulfur dioxide or nitrogen dioxide NAAQS.
The nation continues to experiment with innovative programs to
reduce motor vehicle emissions that cause smog and industrial
emissions that release air toxics and cause acid rain.
Cleaner fuels and cleaner engines, sophisticated emissions testing,
and rethinking of intermodal transportation systems can help increasingly
mobile Americans clean up unhealthy air.
National limits on gasoline volatility-its tendency to evaporate-already
have contributed to lower ozone levels, as observed during the
summers of 1991 and 1992. Oxygenated fuel was introduced during
the winter of 1992-1993, becoming the first major fuel measure
authorized by the Clean Air Act Amendments of 1990 to take effect.
Increasing the oxygen content of gasoline reduces carbon monoxide
emissions by improving fuel combustion, especially in colder temperatures
where fuel combustion is less efficient at the beginning of the
driving cycle. As a result, oxygenated fuels contributed to a
reduction in exceedances of the carbon monoxide standard in the
35 cities implementing the program. Some motorists have complained
that pumping the new fuel at self-service pumps caused dizziness
or headaches. EPA studies into these effects concluded that substantial
risk of acute health symptoms among healthy members of the public
receiving typical environmental exposure is unlikely. Although
chronic developmental, cancer, and non-cancer effects from oxygenated
gasoline cannot be precisely quantified, they are likely to be
no more serious than effects from non-oxygenated gasoline. Nonetheless,
the EPA has provided waivers in some very cold areas (such as
Alaska) while assessing other solutions to reduce emissions.
New Quality Standards. In 1993 new quality standards took effect,
limiting the sulfur content of diesel fuel. The limits will reduce
particulate emissions from in-use diesel engines and pave the
way for particulate-control technology in new diesel engines.
The existing technology is not as effective with high-sulfur fuel.
Cleaner Fuel Regulations. In December 1993 the EPA finalized regulations
that call for a new generation of cleaner, reformulated gasolines
to reduce hydrocarbon and toxic emissions by at least 15 percent
by 1995 and by over 20 percent by 2000 in the nine cities most
polluted with ozone.
Tighter emission standards requiring exhaust hydrocarbon emission
reductions of 30 percent and nitrogen oxide emission reductions
of 60 percent from new cars and light trucks will be phased in
beginning with the 1994 model year. In March 1993 the EPA also
finalized rules requiring a 90-percent reduction in particulate
emissions from new urban buses by 1996.
Enhanced vehicle inspection and maintenance (I/M) may make the
largest contribution toward improved urban air quality of any
measure in the Clean Air Act. The 1990 Clean Air Act has resulted
in the implementation of stricter vehicle tailpipe and evaporative
emission controls that increasingly will benefit all areas over
the next two decades. Enhanced I/M uses high technology testing
on an annual or biennial basis along with supplemental on-road
emissions testing to ensure that vehicles meet these standards.
Maintenance is required to bring nonconforming vehicles into compliance.
The EPA estimates that enhanced I/M, now required in approximately
100 urban areas, can yield a 28-percent emissions reduction. During
1993 the states took the first steps toward implementing the enhanced
I/M program, which will be phased in during 1995.
While emissions from new vehicles on a per-mile basis are a fraction
of the levels of 20 years ago, the number of miles driven has
doubled over that period and continues to rise. The Clean Air
Act of 1990 and the Intermodal Surface Transportation Efficiency
Act of 1991 together require states and local areas to rethink
traditional approaches toward planning and providing transportation
services. In 1993 the EPA finalized a transportation conformity
rule requiring that transportation and air-quality planning be
conducted in concert to maintain air-quality goals. The EPA and
Department of Transportation (DOT) worked together to develop
innovative transportation strategies outlined in a 1993 report,
Clean Air Through Transportation: Challenges in Meeting National
Air Quality Standards. These strategies provide guidance and technical
assistance to state and local governments in reconciling environmental
and mobility goals.
Beginning in 1998 in 22 cities, the EPA will require new fleet
vehicles, such as taxis and delivery vans, to meet tailpipe standards
more stringent than those required for conventional vehicles.
New EPA guidelines provide incentives for fleet owners to purchase
Inherently Low-Emitting Vehicles (ILEV) fueled with natural gas,
propane, pure alcohol, or electricity (see Chapter 7).
Toxic pollutants -those known or suspected to cause cancer or
other serious health effects- are released into the air in many
areas of the United States. Two EPA programs serve as primary
sources of information on air toxics:
. Toxics Release Inventory. The TRI covers air toxics emissions,
and
. National Volatile Organic Compound Database. The database,
in conjunction with field studies, covers air toxics concentrations.
According to estimates of those industries participating in the
TRI, more than 2 billion pounds of toxic pollutants were emitted
into the air in 1991. This is a reduction from 1990, when 2.2
billion pounds were emitted. Among the top-ten air toxics in terms
of quantities reported, TRI emissions showed a downward trend
for all but one of the pollutants listed. The EPA projects that,
with implementation of the Clean Air Act Amendments, this downward
trend will continue.
The EPA is implementing a comprehensive program to reduce routine
emissions of hazardous air pollutants to doses below their known
or suspected levels of causing cancer or other serious health
effects such as birth defects. The Clean Air Act Amendments of
1990 require the EPA to establish standards over a 10-year period
to regulate emissions of 189 chemicals listed in the legislation.
In 1993 the EPA took steps to reduce emissions of hazardous air
pollutants in the following industries:
Dry Cleaners. In September 1993 the EPA issued a final
rule requiring technology controls and/or improved work practices
for 25,000 industrial and large commercial dry cleaners. These
popular businesses are a major source of perchloroethylene, one
of the air toxics that Congress listed for control in the Clean
Air Act. The rule is expected to result in a national reduction
of as much as 35,600 tons per year of perchloroethylene emissions.
Coke Ovens. In October 1993 the EPA issued a final rule
sharply reducing emissions from coke oven batteries. Coke is used
in blast furnaces for the conversion of iron ore to iron in the
process of making steel; the conversion is performed in coke oven
batteries. Coke oven emissions are among the most toxic of all
air pollutants, with preregulation maximum individual risks of
contracting cancer running as high as 1 in 100 in some cases.
The EPA developed the final rule through a formal regulatory negotiation
that included representatives from the steel industry, state and
local agencies, environmental groups, and the Steel Workers Union.
The rule will result in overall reductions of 82 to 94 percent
of total emissions from coke ovens.
Industrial Cooling Towers. In August 1993 the EPA issued
a proposed rule to eliminate emissions of chromium, a highly toxic
chemical, from industrial process cooling towers. The proposed
rule requires substitution of nonchromium-based chemicals for
chromium. The result will be a 100-percent reduction in chromium
emissions from these cooling towers.
Halogenated Solvent Cleaners. In November 1993 the EPA
issued a proposed rule to reduce emissions from solvent cleaning
machines of halogenated solvents including methylene chloride,
perchloroethylene, trichloroethylene, 1,1,1-trichloroethane, carbon
tetrachloride, and chloroform. Major industries using halogenated
solvents include the aerospace industry, motor vehicle manufacturing
facilities, the fabricated metal products industry, and the electric
and electronic equipment industry. The proposed rule, a combination
of equipment standards with work practices, will result in a reduction
of hazardous air pollutant emissions of 88,400 tons per year.
Chromium Electroplating and Anodizing Operations. In November
1993 the EPA issued a proposed rule that will require the application
of maximum achievable control technology for about 5,000 chromium
electroplating and anodizing operations. These operations are
a major emission source of highly toxic chromium compounds listed
for control in the Clean Air Act. The rule is expected to result
in a national reduction of as much as 173 tons per year of chromium
emissions.
During the past 20 years, as outdoor air pollution decreased,
indoor air pollution increased because of the following factors:
. Construction of more tightly sealed buildings,
. Reduction of ventilation to save energy,
. Use of synthetic building materials and furnishings, and
. Use of chemically formulated personal care products, pesticides,
and household cleaners.
Indoor air pollutants include tobacco smoke, radon, volatile organic
compounds, biological contaminants, combustion gases, respirable
particulates, lead, formaldehyde, and asbestos. Diseases such
as asthma, chronic bronchitis, emphysema, and lung cancer-all
of which have increased in the United States over the past two
decades-have been linked to these indoor air pollutants. While
a difference exists in sensitivity from person to person, the
following indoor air pollutants are areas of special concern:
Environmental tobacco smoke (ETS), often called secondhand smoke
or passive smoke, is a major concern. In a December 1992 report,
Respiratory Health Effects of Passive Smoking: Lung Cancer and
Other Disorders, the EPA estimated that ETS causes over 3,000
lung cancer deaths a year among nonsmokers and may be responsible
for serious respiratory illness in hundreds of thousands of children.
As public awareness of the hazards of ETS exposure increases,
businesses and communities across the nation are taking actions
to prevent involuntary exposure through prohibiting smoking indoors
or limiting smoking to specially designated, separately ventilated
smoking rooms. In July 1993 the EPA released a brochure, -What
You Can Do About Secondhand Smoke,- which summarized preventive
actions.
Studies by the National Academy of Science estimate that the naturally
occurring gas, radon, is the cause of 7,000 to 30,000 lung cancer
deaths nationwide each year. Most of these deaths occur among
people who smoke cigarettes. The 1992 Radon Risk Communication
and Results Study, conducted by the State Conference of Radiation
Control Program Directors and sponsored by the EPA, found that
67 percent of Americans show some awareness that radon is a potential
concern; 9 million U.S. homes have been tested for radon; and
300,000 of the 6 million homes estimated to have radon problems
have been treated to mitigate the gas. The study, which yielded
statistics for each state and for target areas within each state,
found greater action to address radon in states with higher radon
potential. Public and private sectors are using the study to establish
a baseline for tracking and improving bottomline environmental
results.
Initially reports of mild symptoms in people working in sealed,
usually recently constructed, office buildings were discounted.
Now scientific experts are reaching agreement that degassing of
certain building materials can cause significant health effects.
The following reasons have led to this conclusion:
Similarity of Symptoms. A remarkable concordance exists
among the kinds of complaints made by workers in different locations
and in different countries. Complaints include headaches, fatigue,
inability to concentrate, and mild inflammation of the eyes and
pharynx. Diary data comparing complaints of symptoms that arise
from working in new office buildings show a remarkable similarity.
Identification of Volatile Organic Compounds. Among the
volatile organic compounds identified as commonly present in buildings
where complaints of symptoms occur are formaldehyde, toluene,
and trichloroethylene. Controlled-exposure studies of these compounds,
such as a recent Danish study of n-decane exposure, find them
to be common in building materials.
During the past several decades, knowledge of factors related
to asthma and other respiratory problems has expanded greatly.
Exposures to a wide range of substances-more than 200 have been
implicated-can induce airway responsiveness. In addition to outdoor
exposure to ozone and sulfur dioxide, these include indoor exposure
to environmental tobacco smoke, toluene, anhydrides, platinum
salts, and some acids and aerosols. Recent data have demonstrated
a correlation between summer pollutant levels and respiratory
morbidity as indicated by hospitalization admissions. Hospital
admissions for asthma have been increasing, along with increases
in asthma mortality. While hospital admissions for asthma declined
for the total population in 1992, they continued to increase for
blacks and other nonwhites and for children.
A total of 20 federal agencies have responsibilities associated
with indoor air quality, either through statutory mandates or
as major property managers.
Committee on Indoor Air Quality. In 1993 the interagency
Committee on Indoor Air Quality (CIAQ), with members from the
EPA, Consumer Product Safety Commission, Department of Energy,
Department of Health and Human Services, and Occupational Safety
and Health Administration, coordinated control efforts.
Legislative Authority. The federal government administers
indoor air programs under the authority contained in statutes
such as Title IV of the Superfund Amendments and Reauthorization
Act (SARA), which requires the EPA to conduct research and disseminate
information on the subject. The Federal Insecticide Fungicide
and Rodenticide Act (FIFRA) and the Toxic Substances Control Act
(TSCA) authorize the EPA to regulate products that adversely affect
indoor air quality.
To reduce the significant health threat of radon, the EPA radon
program has set the following priorities as recommended by a panel
of senior EPA officials and radon experts from outside the agency:
. Target high risk geographic areas and populations that include
smokers;
. Promote radon-resistant new construction techniques;
. Encourage radon testing and mitigation as part of real estate
transfers;
. Sustain a national public education campaign; and
. Develop a coordinated research plan with other federal agencies.
During the last several decades, strong acids (sulfuric and nitric
acids), formed when atmospheric pollutants emitted from power
plants, factories, and motor vehicles combine with water in the
atmosphere, have fallen as acid rain and snow on the northeastern
United States and southeastern Canada. This acidic precipitation
is believed to be responsible for the acidification of sensitive
lakes and streams, damage to historical structures and high-elevation
forests, and impaired visibility in affected areas. The following
are among the technical problems that have been recognized:
. Some watersheds in regions receiving high nitrogen deposition
(such as the Adirondacks and Catskills) and some old-growth forests
in the Appalachians are becoming nitrogen saturated. In many cases
nitrogen inputs are exceeding the capacity of the watersheds to
retain nitrogen and are contributing to increased leaching of
soil nutrients and/or surface water acidification.
. Declines in northeastern high-elevation red spruce forests
are associated with ambient concentrations of pollutants in cloud
water and rain which reduce the midwinter cold tolerance by 4
to 10 degrees Celsius compared with trees growing at the same
locations but at lower elevations.
. Chemical changes in forest ecosystems and surface waters attributable
to acidic deposition are reported in some national parks.
. Wet and dry acidic deposition accounts for an estimated 31
to 78 percent of the dissolution of galvanized steel and copper
in outdoor exposures.
The U.S. Geological Survey coordinates the operation of the National
Trends Network (NTN), a 150-station, nationwide multiagency network
for monitoring precipitation chemistry in the United States. In
addition NTN monitors selected sensitive lakes and streams throughout
the nation to document changes in water chemistry that may result
from the effects of acid rain. The Network also conducts research
in several sensitive watersheds to define how geochemical processes
caused by acid rain affect water quality. NTN data reveal substantial
differences in precipitation chemistry between the eastern and
western regions of the United States. As an example, for the period
1985 through 1993, the following conclusions have been reached:
. Sulfate concentrations are two to three times higher in the
East than in the West, and an apparent decreasing trend for sulfate
concentrations in the East is not evident in the West;
. Nitrate concentrations are consistently higher in the East,
despite the lack of an obvious temporal pattern over the summary
period;
. Ammonium concentrations, uniform across much of the United
States, do not exhibit any temporal pattern;
. Calcium concentrations in precipitation are higher in the West,
although the difference is less than 0.01 milligrams per liter
between regions;
. The combination of higher concentrations of acid anions (sulfate
and nitrate) in the East and similar to somewhat higher concentrations
of cations (ammonium and calcium) in the West results in a consistently
lower pH (higher hydrogen ion concentration) in the East; and
. Although the pH levels are less than one pH unit lower in the
East, the amount of hydrogen in precipitation is five to six times
greater than in the West.
Regional differences evident in concentration data for precipitation
chemistry are even more evident in concentration data for wet
deposition; however, temporal patterns are not as evident. Regional
differences in the amount of precipitation (for instance, the
East has considerably more precipitation than the West but less
year-to-year variability) and concentrations of ions help to explain
the following spatial trends in ionic deposition:
. Wet sulfate and nitrate deposition tends to be four to five
times greater in the East than in the West;
. Ammonium deposition is generally twice as high in the East;
. Calcium deposition is only slightly higher in the East caused
by the offsetting influence of lower concentrations in precipitation;
and
. The average annual difference in the amount of wet hydrogen
deposition in the East relative to the West is eight-fold.
While acidic deposition continues to effect sensitive forest,
soil, and aquatic ecosystems, the effect of recent, relatively
small reductions in the emissions of sulfur dioxide and nitrogen
oxides are difficult to detect.
The EPA administers the Acid Rain Program, which is designed to
achieve significant environmental benefits through reductions
in emissions of sulfur dioxide and nitrogen oxides. To achieve
this goal at the lowest cost, the program employs both traditional
and innovative, market-based approaches for controlling emissions.
It is designed to encourage both energy efficiency and pollution
prevention. Efforts were underway in 1993 to evaluate the costs,
benefits, and effectiveness of the Acid Rain Program as part of
the requirement to assess the costs and benefits of the entire
Clean Air Act. The Acid Deposition Standard Study under section
404 (Appendix B) of the Act will provide insight into the environmental
effectiveness of the Acid Rain Program.
Rules and Guidance. The EPA implements the Acid Rain Program
through an integrated set of rules and guidance:
. Core Acid Rain Final Rules. The agency promulgated these
rules in January 1993 (see Continuous Emissions Monitoring
below);
. Final Allowance Allocation Rules. The EPA promulgated
these rules in March 1993 (Emission Allowance System below);
. NOx Rule. The Acid Rain Program proposed the NOx Rule
for a nitrogen oxides emission reduction program in November 1992;
the Clean Air Act calls for a 2-million-ton reduction in NOx emissions
by the year 2000;
. Opt-In Rule. This rule allows sulfur dioxide emitting
sources other than electric utilities to participate in the Acid
Rain Program, providing the opportunity for further low-cost reductions
of sulfur dioxide emissions; the final Opt-In rule for combustion
sources was published in the Federal Register on September 24,
1993.
Continuous Emission Monitoring (CEMs). Implementation of
the acid rain core rules was underway in 1993. All 110 sources
subject to Phase I of the sulfur dioxide emissions reduction program
have submitted permit applications; draft permits were issued
in August 1993, and one-third of the final permits were issued
in 1993. The EPA has reviewed over 100 Phase I Continuous Emission
Monitoring (CEM) plans, and affected utilities have installed
and tested 900 CEMS. Emissions data for Phase I sources were submitted
to EPA in January 1994.
Emission Allowance System. To achieve a 10 million_ton
reduction in sulfur dioxide emissions, the Acid Rain Program administers
an emission allowance system, by which the EPA allocates emission
allowances to electric utilities in designated amounts that reflect
an overall cut in emissions. To achieve these reductions, the
law requires a 2_phase reduction in emissions from fossil fuel_fired
power plants. A nationwide cap of 8.95 million tons of sulfur
dioxide will be maintained with individual units deciding their
own plan for compliance, as long as they stay within their allowance
limit. A utility can cut its emissions more than required and
sell its extra allowances to another utility or bank them for
future use. At the end of each year, utilities must hold enough
allowances to cover their emissions. Noncompliance earns automatic
penalties.
Emission Allowance Trades and Auctions.
Emisson Allowance Trades and Auctions. A limited number
of two-party and brokered trades are occurring in the allowance
market, with announced prices ranging from $250 to $350 per allowance.
On March 29, 1993, the EPA held an auction conducted by the Chicago
Board of Trade, which has been delegated the administrative functions
of the allowance auction. About 150,000 allowances were sold with
selling prices ranging from $122 to $450 per allowance. Private
auctions are expected to occur when the EPA allowance tracking
system becomes operational in 1994.
Conservation Verification Protocols. In March 1993 the
EPA published Conservation Verification Protocols to provide guidance
on energy conservation to the regulated community. The system,
in which each ton of sulfur dioxide a utility avoids emitting
means one fewer allowance retired and one more that can be sold
at a profit, creates an inherent incentive for utility energy
conservation.
The National Acid Precipitation Assessment Program (NAPAP) was
reauthorized under Title IX of the 1990 Clean Air Act Amendments
(CAAA) to monitor and assess the effects of the Acid Rain Program
(Title IV, CAAA). NAPAP coordinates the federal acidic deposition
research and monitoring program in addition to its new charges
of evaluating the costs of Title IV and determining the reduction
in deposition rates needed to prevent adverse ecological effects.
As required by the CAAA, NAPAP reports to Congress on its investigations,
analysis, and assessments. The first of these reports, which was
issued in 1993, summarizes the evolution of public policy, regulatory,
and technical environments within which NAPAP is operating and
updates the results of relevant scientific investigations and
analysis. Evaluation of costs and benefits will be addressed by
NAPAP under section 901 of the Clean Air Act, with reports issued
every four years beginning in 1996.
Global climate change and the effect of greenhouse gases on it
were the major climate issues of the year, along with temperature
and precipitation extremes in the United States which varied from
ice storms to heat waves and from droughts to disastrous floods.
Climate, the average weather in an area over a long period of
time, can be described in terms of temperature, precipitation,
humidity, sunshine, atmospheric pressure, and wind conditions
that prevail at different times of the day or year. Other factors
include extremes in range, variability, and frequency of variation.
Checking the long_term record, the contiguous United States experienced
lower than average temperature but higher than average precipitation
during 1993.
The year 1993 started out with moderate average monthly temperatures
for most of the country, but, as the year progressed, large areas
experienced temperatures of both extremes. By July 1993 a sixth
of the country was reporting very warm conditions, while at the
same time about a third of the contiguous United States was experiencing
very cold conditions. The -very warm- category is defined statistically
as that monthly average temperature (or warmer) occurring less
than 10 percent of the time throughout the 99-year U.S. climate
data record; -very cold- is similarly defined for the cold end
of the scale.
Statewide temperature ranks for May-August 1993 showed very warm
anomalies along the east coast and very cold anomalies in the
northwestern quarter of the country. Seven states ranked among
the warmest on record while four states ranked among the coldest.
Unusually cold temperatures occurred for at least a tenth of the
country through mid-summer to late fall (July-November), with
over a fourth of September readings and nearly a third in November
unusually cold. The cold anomalies were located largely from the
Central Plains to the Pacific Northwest. In 1993 despite extreme
spring and summer temperatures in the Southeast, the contiguous
United States as a whole had the 13th coldest year on record.
Parts of the United States experienced excessive precipitation
during 1993, but other parts were exceptionally dry. The year
started out wet, with more than a fourth of the country experiencing
very wet conditions in January, and a sixth of the country reporting
very wet conditions in February. The -very wet- category is defined
statistically as that amount of precipitation (or greater) occurring
less than 10 percent of the time throughout the 99-year U.S. climatic
data record; -very dry- is similarly defined for the dry end of
the scale. Both very wet and very dry conditions occurred during
the summer months: more than a fifth of the country was very wet
in June and more than a fourth was very wet in July, while over
a fourth was excessively dry during July and a seventh during
September.
The period May-August 1993 was characterized by extreme precipitation
anomalies. Excessive rains occurred from the Northwest to the
Midwest, while severe dryness occurred along the east coast. Using
statewide precipitation ranks based on 1895-1993 data, the May-August
1993 period showed 14 states with among the wettest periods on
record; Iowa, Montana, and North Dakota ranked as the wettest
on record. Thirteen states had among the driest May-August periods
on record, with North Carolina ranking as the driest. In 1993
the contiguous United States as a whole had the 13th wettest year
on record.
Record flooding occurred along parts of the Mississippi River
during the summer of 1993, causing record property and crop damage
and closing the river to ship and barge traffic (see Chapter 2:
Water Quantity and Quality). Based on 99-year data, the upper
Mississippi River basin in 1993 had the wettest April-August period
ever. Ironically only five years ago, ship and barge traffic was
halted due to near-record dryness reminiscent of the persistent
drought of the 1930s.
Much of the primary corn and soybean agricultural region is located
within the Mississippi River basin. In 1993 this agricultural
belt had the wettest June-September on record; this period encompasses
much of the growing/harvesting season.
The Southeast region of the United States in 1993 had the driest
May-August period in the 99-year record. Severe crop losses occurred
in South Carolina and parts of North Carolina and Georgia because
of the drought.
The dryness of summer 1993 rapidly increased the percentage of
the South Atlantic-Gulf Coast drainage basins with severe to extreme
drought, reaching about 10 percent of the region by August 1993,
with another 50 percent of the region in the moderate drought
category. The severe drought area persisted at about the 10-percent
level through the end of 1993. This occurred after a 2-year respite
from severe drought in the region.
In August 1993 about 43 percent of the contiguous United States
suffered under severely to extremely wet conditions. By this measure,
only four other wet episodes in this century (1915, 1941, 1973,
and 1983) have been as severe.
Only 15 percent of current U.S. coastal residents have experienced
a major hurricane, but with the population in storm-vulnerable
coastal counties growing rapidly, increasing numbers of people
are being exposed to such risks. New residents are the least experienced
with hurricanes, but because of a long absence of disastrous hurricanes
along most of the coast, even longtime residents have little hurricane
experience.
The total amount of real property exposed to the risk of hurricanes
is staggering. Hurricane Andrew in 1992 caused estimated direct
losses of $26 billion, with indirect losses to businesses of another
$15 billion; yet it could have been much worse. Had Andrew struck
a mere 20 miles farther north in the financial/business center
of Miami, the direct damage could have been $70 billion, with
even higher indirect business losses. Andrew sent shock waves
through the U.S. economy when several insurance companies failed
and later when wind insurance premiums increased tenfold. Each
decade holds the potential for several hurricanes like Andrew
or worse.
During the first 90 years of this century, the United States suffered
direct hits by 60 major hurricanes, an average of two out of every
three years. Each of these storms now has the potential to be
a multibillion-dollar event. The risk of larger hurricane disasters,
in terms of loss of life and damage, is increasing. Coastal communities
need to address hurricane preparedness on every possible front.
Forecast Uncertainty. The nation still faces uncertain
hurricane forecasts. Increased precision in forecasting the point
of impact and the strength of the hurricane could limit the population
to be evacuated to a level that existing roads could handle. The
simple provision of longer lead times and more targeted warnings
would allow the repositioning of rolling stock-buses, trucks,
recreational vehicles, airplanes, trains, and even boats-thus
removing this expensive property from harm's way.
Overdevelopment. A second problem results from the overdevelopment
of coastlines. More realistic land-use policies would minimize
the growth of the population at risk. The nation needs policy
changes to modify or eliminate federal programs that subsidize
or otherwise encourage development in the vulnerable coastal zone.
Communities need local planning to provide limited, targeted evacuation
and last-resort refuges for those who do not evacuate in time.
Unnecessary Preparations. Improved hurricane forecasting
and response offers a potential payoff by reducing unnecessary
preparations. Such reductions, which could save millions of dollars,
depend ultimately on more precise and targeted hurricane warnings.
Lax Building Codes. The potential savings from well-timed
preparations in areas hit by a hurricane are even more impressive
than savings from the reduction of unnecessary preparations. A
good building code was in effect for Andrew in Dade County, Florida,
but compliance was deficient. Good code enforcement and inexpensive
hurricane shutters could have reduced damages by several percentage
points. Such savings would have been significant, considering
that 1 percent of the Andrew damage equalled $260 million. Building
codes are not as good for the rest of the nation's coastal areas,
and thus strict enforcement of better codes represents an area
where hurricane preparedness can have a substantial impact.
A major hurricane has yet to hit a large coastal city in modern
times, but with the concentration of population along the coast,
such an event is inevitable. City infrastructures, including roads
and bridges, have not kept pace with population increases, leaving
in question the ability of cities to quickly evacuate large populations
along the Atlantic and Gulf of Mexico coastlines. Despite increased
emergency planning, the record of decreasing hurricane fatalities
in this century could be in jeopardy.
In 1993 the United States experienced 1,173 tornadoes across the
country, above the long-term 30-year average of 863 but lower
than the 1992 record of 1,297. State-by-state distribution shows
that the majority of these storms occurred in tornado alley-that
area of the central United States and Gulf coastal plain with
a historically high annual probability of tornado occurrence.
In 1993 several states reported record numbers of tornadoes:
State Number of Tornadoes
South Dakota 85
Minnesota 47
Virginia 28
Idaho 11
Utah 6
The 1993 death toll was below normal at 33 compared to the average
of 82. In the decade ending in 1980, the tornado death toll in
the United States was 953. For the 10-year period ending in 1993,
that figure had decreased to 536. Several factors have contributed
to this trend:
National Severe Storms Forecast Center. The NSSFC is responsible
for monitoring current and projected weather patterns to alert
the public of the potential for severe weather episodes. The success
of this program is measured in the decline in deaths.
National Weather Service Warning Program. Improvements
in the NWS warning program have allowed it to reach more citizens,
helping them to take precautions for tornadoes.
Local Weather Service Offices. Preparedness efforts sponsored
by local weather service offices have raised public awareness
of the threat.
Emergency Managers and Volunteers. Safety and preparedness
efforts by emergency managers, volunteer spotters, and ham radio
operators also have produced a more enlightened public.
The frequency of tornadoes in the United States would seem to
indicate a sharp increase in tornado activity in recent years.
A detailed examination of the data, however, shows that this is
not the case. The explanation is better detection. U.S. tornadoes
dating back to 1953, if categorized by intensity-the weak ones
versus the strong or violent ones-show a dominance of weak tornadoes.
These account for most of the variability and rise in tornado
totals that culminated in the record or near record totals for
the past four years. One of the factors that has caused this phenomenon
is a greater emphasis on report gathering and warning validation
by the NWS. Increased populations, storm chasing, and the advent
of the video camera have also contributed to the detection of
weaker tornados that previously might have been missed. Since
the numbers of strong and violent tornadoes have not undergone
the growth exhibited by weak tornadoes, it is likely that significant
tornadoes represent the true tornado climatology.
While human activities have long influenced local environments,
only since the start of the Industrial Revolution and subsequent
rapid population growth have human activities begun to have a
significant influence on the global environment. These activities
are inducing changes in the earth system which may have major
environmental consequences: long-term climate change and greenhouse
warming, stratospheric ozone depletion and increased ultraviolet
(UV) radiation, changes in natural seasonal to interannual climate
variability, and large-scale changes in land cover and terrestrial
and marine ecosystem productivity. Understanding the causes and
implications of large-scale global environmental change is instrumental
in determining what courses and actions must be considered now
and in the future to ensure the compatibility of economic growth,
protection of the global environment, and long-term sustainability
of the quality of life.
Trace gases in the atmosphere comprise only about 1 percent of
its composition but provide two vital functions: they warm the
earth's surface by trapping infrared (heat) energy in the atmosphere;
and they shield the planet from harmful radiation. These gases
are referred to as greenhouse gases. Their warming capacity, called
the greenhouse effect, is essential to maintaining a climate hospitable
to all life forms.
Greenhouse gases regulate the global climate by stabilizing the
balance between the earth's absorption of heat from the sun and
its capacity to reradiate heat back into space. Activities that
can change this balance include natural, such as changes in solar
radiation and volcanic eruptions, and human-induced, arising from
industrial and land-use practices that release or remove heat-trapping
greenhouse gases, thus changing atmospheric concentration. Greenhouse
gases include water vapor, carbon dioxide, methane, nitrous oxide,
chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs),
hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and ozone
in the lower stratosphere and troposphere. While water vapor has
the largest effect, its concentrations are not directly affected,
on a global scale, by human activities. Most of these gases occur
naturally, the exceptions being CFCs, HCFCs, HFCs, and PFCs, but
human activities'combustion of fossil fuels, deforestation, rice
cultivation, mining, and the use of nitrogen fertilizers, refrigerants,
and solvents'have contributed to increases in their atmospheric
concentrations. Internationally accepted science indicates that
increasing concentrations of greenhouse gases ultimately will
raise atmospheric and oceanic temperatures and could alter associated
circulation and weather patterns. Many greenhouse gases have long
atmospheric residence times- several decades to centuries-which
implies that the atmosphere will recover very slowly, if at all.
Since 1990 U.S. emissions of carbon dioxide have increased while
emissions of other greenhouse and photochemically important gases
have remained constant or have declined. A summary of trends for
the main greenhouse gases follows.
Carbon Dioxide. Large natural sources and sinks of carbon
dioxide function in a balanced cycle, with human activities accounting
for a smaller, but increasingly important source of emissions.
Global atmospheric concentrations of carbon dioxide have increased
about 30 percent since the 1700s, suggesting that the natural
carbon cycle may be out of balance. This increase is responsible
for more than half of the global -heat trapping- or -radiative
forcing- due to human activities.
Since the 1950s observations of carbon dioxide have shown regular
annual increases in both concentration and rate of concentration
growth, with year-to-year variations in growth rate. During the
period 1991 to 1993, the rate of increase of carbon dioxide per
year slowed, substantially and inexplicably, to as low as 0.5
parts per million by volume (ppmv) per year from as high as 1.5
ppmv per year. Numerous examples exist of short periods where
growth rates are higher or lower than the long-term mean. The
most recent observations indicate that growth rates of carbon
dioxide are increasing again.
The main anthropogenic sources of carbon dioxide are the burning
of fossil fuels (with additional contributions from cement production)
and land-use changes. In the United States, anthropogenic emissions
are divided fairly evenly among sectors. Fossil-fuel combustion
produces 99 percent of the total gross U.S. emissions. The industrial
sector is the largest source of fossil-fuel carbon dioxide emissions
while the transportation sector, second to industry in quantity,
had the fastest growth rate in emissions during the last decade.
Cement production involving the calcination of limestone, lime
production, steel making, and industrial carbon dioxide production
account for the remaining 1 percent of total emissions. Absorption
of carbon dioxide in U.S. forests (carbon -sinks-) has increased
in recent years.
The United States is the world's largest source of energy-related
carbon dioxide emissions, followed by the former Soviet Union
and China, India, and Germany. In 1950 U.S. fossil-fuel carbon
dioxide emissions accounted for more than 40 percent of global
emissions; since then, however, this share has steadily declined
to 22 percent. Emissions in the developing world, while a relatively
small portion of the total, continue to rise rapidly, particularly
in the Far East.
Methane is a potent greenhouse gas. Considering only its
heat-absorption potential, one molecule of methane has 20 times
more effect on climate than one molecule of carbon dioxide. Global
concentrations of methane in the atmosphere have more than doubled
over the last two centuries and since 1983 have increased by 7
percent, even though the globally averaged methane growth rate
declined. Recent data suggest that the growth rates started to
increase in late 1993.
Scientists have concluded that atmospheric increases in methane
are largely caused by increasing emissions from anthropogenic
sources, such as landfills, agricultural activities, fossil fuel
combustion, coal mining, the production and processing of natural
gas and oil, and wastewater treatment. Landfills are the largest
source of methane emission in the United States-they represent
a third of U.S. methane emissions-followed by emissions from agriculture
(primarily cattle production) and emissions from oil, gas, and
coal production collectively.
Methane is also produced naturally via anaerobic decomposition.
Wetlands provide the largest natural source, followed by termites.
While termites are only a trivial natural methane source in temperate
zones, they are ubiquitous in the tropics and when tropical forests
are logged or burned, vast quantities of wood residue provide
ideal conditions for termite population explosions.
Nitrous Oxide. Nitrous oxide, commonly known as laughing
gas, is a potent, stable greenhouse gas with a long atmospheric
lifetime, from 120 to 150 years. Although actual emissions of
nitrous oxide are smaller than those of carbon dioxide, nitrous
oxide is approximately 270 times more powerful than carbon dioxide
at trapping heat in the atmosphere over a 100-year time horizon.
The many small sources of nitrous oxide, both natural and anthropogenic,
are difficult to quantify. A best estimate of the current (1980s)
anthropogenic emission of nitrous oxide is 3 million to 8 million
metric tons per year. Natural sources are probably twice as large.
Atmospheric concentrations of nitrous oxide have increased by
8 percent over the last century, which is most likely due to human
activities. The average growth rate over the past four decades
is about 0.25 percent per year (0.8 parts per billion per year).
The primary source of nitrous oxide emissions in the United States
is agricultural fertilizer use and soil management. Lesser sources
include fossil fuel combustion by mobile and stationary sources,
adipic acid production, nitric acid productions, and burning of
agricultural crop residues.
Halocarbons. Halocarbons containing fluorine, chlorine,
and bromine are significant greenhouse gases on a per molecule
basis. Direct radiative forcing (heat trapping) due to increases
in halocarbons since pre-industrial times represents about 12
percent of the greenhouse gas contribution. Chlorine from chlorofluorocarbons
(CFCs), carbon tetrachloride, and methyl chloroform and bromine
from halons are also linked to stratospheric ozone depletion to
varying degrees. CFCs have been long and widely used as refrigerants,
foaming agents, solvents, and aerosol propellants. Carbon tetrachloride
and methyl chloroform are industrial solvents, and halons are
used in fire suppressors. Emissions of many such ozone-depleting
compounds are controlled by the Montreal Protocol and its subsequent
amendments and adjustments:
. The Montreal Protocol. The 1987 Montreal Protocol on
Substances that Deplete the Ozone Layer calls for a 50-percent
reduction in the use of chlorofluorocarbons (CFCs) by 1995, using
1986 usage levels as baseline.
. The London Amendment. The subsequent London Amendment
calls for the complete elimination of CFC use by 2000.
. The Copenhagen Amendment. The proposed Copenhagen Amendment,
to be ratified in 1994, accelerates the complete phaseout of CFCs
to January 1, 1996.
The tropospheric growth rates of the major anthropogenic source
species for stratospheric chlorine and bromine have slowed significantly
in response to these international agreements. For example the
1993 CFC-11 annual growth rate was 25 to 30 percent of that observed
in the 1970s and 1980s. The total amount of organic chlorine in
the troposphere increased by only 1.6 percent in 1992, about half
of the rate of increase (2.9 percent) in 1989. Total peak chlorine/bromine
loading in the troposphere is expected to occur in 1994, but the
stratospheric peak will lag by about three to five years, so stratospheric
abundance will continue to grow for a few more years before declining.
Several substitutes for CFCs and other ozone-depleting substances
are now being manufactured and used, including hydrochlorofluorocarbons
(HCFCs) and hydrofluorocarbons (HFCs). Growth in atmospheric concentrations
of HCFCs has been observed for several years and is currently
about 7 percent per year. The direct global warming potential
of most HCFCs and HFCs are less than those of the compounds they
replace, although some HFCs have substantial global warming potentials.
Perfluorocarbons, which have been proposed as CFC substitutes
in some applications and are by-products of some industrial processes,
including aluminum production, have very long atmospheric lifetimes
(several thousand years) and are extremely powerful greenhouse
gases. Because they are not harmful to the ozone layer, they are
not controlled by the Montreal Protocol. Because of their greenhouse
effect, however, they will be considered under the Framework Convention
on Climate Change.
Ozone is an important greenhouse gas present in both the stratosphere
and troposphere. In the troposphere ozone is produced from various
precursor gases (carbon monoxide, nitrogen oxides, and non-methane
hydrocarbons) and as a result of chemical feedbacks involving
methane. Tropospheric ozone-a key component of smog-has increased
above many locations in the Northern Hemisphere over the last
30 years. This is a cause for concern because tropospheric ozone
acts as a strong absorber of infrared radiation and in high concentrations
causes respiratory distress in humans. In the Southern Hemisphere,
a decrease has been observed since the mid-1980s at the South
Pole; in the hemisphere as a whole, data are insufficient to draw
strong inferences.
In the stratosphere ozone is continually being formed and destroyed
by chemical reactions. Large natural changes occur in stratospheric
ozone concentration; for example between summer and winter, a
change of about 25 percent can occur at mid-latitudes. Stratospheric
ozone depletion occurs if the rate of ozone destruction becomes
faster than its rate of formation, either because of natural causes
or human activities. Over the past 15 to 20 years, loss of stratospheric
ozone caused by CFCs and halons may have partially offset their
direct warming effect. Stratospheric ozone depletion is also linked
to increases in ultraviolet (UV) radiation.
Long-term global satellite and ground-based monitoring data indicate
that stratospheric ozone depletion has been occurring over most
of the globe, except in the tropics, since late in the 1970s.
The most dramatic evidence of this decline is the springtime ozone
hole in the Antarctic. Downward trends of several percent per
decade are now observed in all seasons at mid-latitudes (poleward
of 20 degrees) in both hemispheres, with winter and springtime
declines of as much as 6 to 8 percent per decade observed poleward
of 45 degrees. Global ozone depletion worsened significantly in
1992 and 1993, including wintertime depletions of up to 25 percent
over populated regions in the high latitudes of the Northern Hemisphere.
The observations of unprecedented and unexpected ozone depletion
in 1992 and 1993, coinciding with the period following the eruption
of Mt. Pinatubo, have revealed new gaps in scientific understanding
and, hence, in prognostic capabilities. While ozone levels may
have been perturbed by the Mt. Pinatubo eruption, either by changes
in stratospheric temperature and/or circulation or by enhanced
heterogeneous chemistry, the magnitude and timing of the recent,
large ozone decreases are not fully explained by the current understanding
of these effects. Consequently evaluation of the heterogeneous
chemistry associated with surface reactions on aerosols through
laboratory studies, atmospheric observations, and modeling remains
a research priority.
Antarctic Ozone Hole. Each winter the atmosphere over Antarctica
is isolated from the rest of the world by the polar vortex. It
is dark and very cold, resulting in the formation of clouds in
the ozone layer of the stratosphere. When the sun shines on Antarctica
again in springtime, chlorine in these clouds causes local depletion
of ozone, thus creating the ozone hole. The hole disappears when
the Antarctic atmosphere warms up enough to break up the circulation
which isolates it from the rest of the world. Ozone-rich air then
flows in to replenish the ozone layer over Antarctica. The springtime
Antarctic ozone hole has been growing successively larger and
more intense since the 1960s. Now the springtime (October) average
total ozone values over Antarctica are 50 to 70 percent lower
than those observed in the 1960s. In 1993 the ozone hole over
Antarctica produced the lowest values of ozone ever recorded anywhere
in the world. The ozone hole is expected to reach its most severe
levels early in the next century, and recovery is estimated to
take 70 years.
Environmental Implications. Significant increases in ultraviolet
(UV) radiation have been observed in conjunction with periods
of intense ozone depletion. Analysis of fauna living in the Antarctic
region, analysis of health data, and field and laboratory experiments
indicate that increases in UV levels may have significant deleterious
impacts on human health, fish populations, and, if sustained,
most of the earth's ecosystems. In humans and other terrestrial
and aquatic organisms, impacts can include immune system suppression,
sunburn, cataracts, lesions, reduced vitamin D synthesis, and
cancers which can result in reduced fitness and death. In plants
UV can inhibit the photosynthetic process and result in the death
of organisms.
Changes in UV exposure also relate to issues concerning changing
species diversity and agricultural productivity and induce adverse
effects on materials such as plastics. The 1993 springtime ozone
hole over Antarctica allowed record levels of UV light to reach
Antarctica. At one Antarctic monitoring site, UV-B, the part of
the spectrum most harmful to life, was recorded at levels 44 percent
higher than in 1992. Investigations are now underway on the impact
that the increased UV might have on life on and around Antarctica,
and on whether animals and plants may have mechanisms to avoid
harm from increased UV. Current UV levels have already reduced
productivity of ocean phytoplankton-microscopic plants that comprise
the base of the Antarctic food chain-by 6 to 12 percent in areas
affected by the ozone hole.
Stratospheric ozone depletion is also linked to changes in the
surface climate. Loss of lower-stratospheric ozone is predicted
to lead to a cooling tendency at the surface. As a result of this
effect, ozone decreases offset some of Mt. Pinatubo eruption,
either by changes in stratospheric temperature and/or circulation
or by enhanced heterogeneous chemistry, the magnitude and timing
of the recent, large ozone decreases are not fully explained by
the current understanding of these effects. Consequently evaluation
of the heterogeneous chemistry associated with surface reactions
on aerosols through laboratory studies, atmospheric observations,
and modeling remains a research priority.
The greenhouse warming of the halocarbons that caused the ozone
change. Such indirect couplings complicate projection of changes
in the global climate.
The United Nations Montreal Protocol (1987) and its amendments
are being implemented to phase out production of ozone-depleting
compounds. Even if the control measures are fully implemented,
however, ozone depletion will continue for nearly another decade.
Because of the long atmospheric lifetimes (up to 100 years) of
many of the halocarbons, the earliest recovery of the Antarctic
ozone hole is several decades away, and a return to near-natural
atmospheric levels of chlorine and bromine, and therefore of ozone,
will take centuries.
Modeling studies suggest that, in contrast to greenhouse gases,
anthropogenic particles in the atmosphere derived from sulfur
dioxide emissions from coal and oil combustion and heavy industrial
processes and from biomass burning can lower surface temperatures.
Research on the radiative effects of these atmospheric aerosols
is important to understand whether aerosols may be, in the near-term,
offsetting the enhanced greenhouse effect of carbon dioxide. Recent
studies suggest that the hemispheric asymmetry in this century's
warming may be due, at least in part, to the preferential presence
of sulfate aerosols in the Northern Hemisphere as a result of
industrial emissions patterns.
Natural factors can exert positive or negative radiative forcings.
For example since about 1850, a change in the sun's output may
have resulted in positive radiative forcing. In contrast some
volcanic eruptions, such as that of Mt. Pinatubo in June 1991,
result in short-lived (a few years) increase in aerosols in the
stratosphere, causing a large, but short-lived negative radiative
forcing. The effect of the Mt. Pinatubo eruption has been detected
in the observed temperature record.
The accumulated evidence suggests that global climate change may
be occurring. Among the indicators changes in surface air temperatures
provide the most direct evidence. Global mean surface temperature,
as indicated by the long-term measured climate record, has increased
between 0.3 and 0.6 degrees Celsius over the past century. The
observed warming over parts of the Northern Hemisphere mid-latitude
continents largely characterized by increases in minimum (night-time)
rather than maximum (day-time) temperatures. Scientists and governments
around the world agree that if the current rate of increase in
anthropogenic emissions of greenhouse gases continues, the global
mean temperature will likely warm between 1.5 and 4.5 degrees
Celsius over the next century.
Additional evidence for global climate change can be gleaned from
observational and satellite records of precipitation over land
areas in middle latitudes and in the tropics, areal extent of
snow cover, date of snow cover disappearance in the Arctic, trends
in sea-ice extent in the Arctic and Antarctic regions, melting
of glaciers outside the polar zone, and sea-level rise.
Alterations of natural systems-clearing land for agriculture,
logging forests, or reclaiming swamps-have impacts on emissions
and absorption of greenhouse gases but consequences whose magnitude
is uncertain. Improved predictions of the response of terrestrial
ecosystems to changes in temperature, rainfall, solar radiation,
especially UV radiation, and changes in carbon dioxide concentrations
will enable the development of management strategies for reducing
damage to valuable ecosystems.
The predicted increases in global mean temperature are likely
to lead to shifts in precipitation patterns and rising sea level.
Although the implications of these changes is not fully understood,
it is climate change that poses the most serious threat to human
health, global productivity, and worldwide economic stability.
Prospective changes in precipitation patterns from climate change
are predicted to lead to important shifts in world agricultural,
forestry, and grassland regions and in the availability of water
resources, with the possibility of altering long-established patterns
of land use. The growth rate of some plants might be increased
in the presence of additional carbon dioxide-called the -fertilization
effect-. Together these changes have the potential to cause important
shifts in habitat for flora and fauna. Although average global
food productively may not be affected adversely by climate change,
local effects, especially in developing countries, could lead
to hunger, malnutrition, and large-scale human migrations.
Climate change also poses a threat to forestry and fishery resources.
Recent studies suggest that forest health may be impacted by negative
synergisms among depositional pollutants (such as acid rain),
global change parameters (such as elevated carbon dioxide), and
biotic stresses (such as insect feeding). Slight changes in salinity
or temperature may impact adversely larval stages of fish, the
most vulnerable life stage to environmental change.
The warming of the oceans and the melting of icecaps and glaciers
will result in sea level rise. The amount of sea level rise over
the next century is projected to be tens of centimeters (several
times the rate of rise in the recent past), which could lead to
coastal flooding, the loss of valuable wetlands, and increased
threats to coastal areas from storm surges and hurricanes.
Although there has been little research to date on the human health
effects from climate change, such effects could range from increases
in vector-borne diseases to higher mortality rates during increased
conditions of excessive heat and air pollution, particularly in
areas with a high incidence of poverty.
Estimates of human-induced changes in land-cover vary according
to the system of land-cover classification used, but to provide
some examples, human activities over the last three centuries
have resulted in a net loss of approximately 2.32 million square
miles or 6 million square kilometers of forest (an area slightly
smaller than Australia); a net gain in cropland of approximately
4.6 million square miles or 12 million km2 (an area approximately
the size of the United States and Mexico); and a net loss of approximately
0.62 million square miles or 1.6 million km2 of wetlands.
While the direct effects of land-cover changes on global environmental
systems are not precisely understood, it is generally accepted
that changes in land-cover from human activities have resulted
in a net flux of carbon dioxide to the atmosphere approximately
equal to the net release over the same period from fossil fuel
burning, with land-use and land-cover change representing the
largest human source of emissions of nitrogen dioxide. The potential
impacts of land-cover changes on climate can only be crudely assessed
at present. Much attention has been focused on the effects of
deforestation of large areas of tropical rainforest and the resulting
changes in radiative forcing through release of carbon into the
atmosphere. But land-cover changes also affect regional climate
by altering surface runoff, temperature, and wind speed. In the
United States, recent trends in land use such as the abandonment
of farmland and the increase in forest area should enhance natural
absorption of carbon dioxide and methane while reducing emissions
of nitrous oxides associated with agricultural fertilizer use.
The focus in 1993 was on global environmental change. President
Clinton announced on Earth Day 1993 that the United States was
committed to reducing greenhouse gas emissions to the 1990 level
by the year 2000. Other accomplishments included a new Climate
Change Action Plan and measures to help implement the Framework
Convention on Global Climate Change, to protect the stratospheric
ozone layer, and to phase out CFC-production.
The United States is signatory to the 1992 Framework Convention
on Climate Change that commits nations to the aim of reducing
emissions of greenhouse gases and to the Montreal Protocol that
strives to phase out production of CFCs and other ozone-depleting
substances. In 1993 the United States undertook a number of programs
that helped comply with these agreements.
On the occasion of the 24th Earth Day, April 21, 1993, President
Clinton announced that the United States was committed to reducing
greenhouse gas emissions by the year 2000 to their 1990 levels
and promised a plan to outline steps for achieving these levels.
At the 1992 Earth Summit in Rio the United States had joined more
than 150 other countries in signing the Framework Convention on
Climate Change, whose objectives are to stabilize greenhouse gas
concentrations in the atmosphere at a level that would prevent
dangerous anthropogenic interference with the climate system within
a timeframe sufficient to allow ecosystems to adapt naturally
to climate change, to ensure that food production is not threatened,
and to enable economic development to proceed in a sustainable
manner. As of December 21, 1993, the Framework Convention had
been ratified by 50 countries and was scheduled to enter into
force in 1994.
In October 1993 President Clinton released a blueprint for reducing
greenhouse gas emissions, The Climate Change Action Plan. The
plan will provide a foundation for the National Report required
under the Framework Convention on Climate Change that will describe
the policies, programs, and measures the United States is taking
to reduce greenhouse gas emissions. The plan targets all greenhouse
gases and calls for 50 actions involving many sectors of the economy-industry,
transportation, homes, office buildings, forestry, and agriculture.
Examples follow.
Forests as Carbon Sinks. One action would reduce carbon
dioxide emissions by protecting forests, which are natural greenhouse
gas sinks.
Climate Challenge. The Department of Energy (DOE) has formed
a new partnership with major electric utilities who have pledged
to reduce greenhouse gas emissions. Participating utilities may
choose from a range of control options and experiment with innovative
ideas to achieve their emission reduction goals.
Climate Wise. As part of this joint program cosponsored
by the DOE and the EPA, firms who agree to reduce greenhouse gas
emissions set bottom-line emission targets that they can attain
using the most cost-effective means available.
DOE Motor Challenge. This new initiative sponsored by the
DOE, motor system manufacturers, industrial motor users, and utilities
promotes installation of the most energy-efficient motor systems
in industrial applications.
EPA Partnerships. Chemical companies are working with the
EPA to reduce byproduct emissions of potent greenhouse gases by
50 percent from their manufacturing operations. Aluminum producers
joined with the EPA to identify opportunities to reduce greenhouse
gas emissions and set targets for real reductions.
U.S. Initiative on Joint Implementation. In addition to
reducing greenhouse gas emissions with domestic actions, the Plan
lays the foundation for an international response. The Framework
Convention encourages countries to explore emission reduction
projects together under a program of joint implementation. To
gain experience in verifying net emission reductions from certain
types of investments in other countries, the U.S. Initiative on
Joint Implementation will develop projects to provide greenhouse
gas reductions beyond the domestic programs and promote sustainable
development. The initiative will advance thinking on issues that
need resolution before an international joint implementation effort
can be fully mounted.
The interagency team assigned by the President to develop a new
Climate Change Action Plan relied heavily on public input. For
that purpose the team helped organize the White House Conference
on Global Climate Change, held on June 10-11, 1993, in Washington,
D.C. The conference provided the opportunity for hundreds of recognized
experts to offer their suggestions and views. The Climate Change
Action Plan was released in October 1993.
The EPA continued to promote green programs that encourage the
voluntary introduction of new energy-saving technologies in the
marketplace. Accomplishments in 1993 included the following:
Natural Gas Star Program. In March 1993 the natural gas
industry and the EPA launched this voluntary partnership to reduce
methane emissions from their operations. The 16 participating
companies represent 40 percent of U.S. gas transmission and distribution
systems. Potential savings from the program could reach 1 million
metric tons of methane-the CO2 equivalent of removing 3 million
cars from the road.
Energy Star Computers. These computers have a feature that
allows the machine to reduce its power consumption automatically
or -go to sleep- when not in use. Energy Star computers entered
the market in 1993;
Ozone-Friendly Refrigerators. Whirlpool won a $30 million
contract in a contest sponsored by an electric utility consortium
to provide consumers with energy-efficient, ozone-friendly refrigerators;
and
Green Lights Program. This initiative, which encourages
companies to replace their existing lighting with new, energy-efficient
lighting fixtures, grew to over 1,000 participants in 1993.
The United States continued to make progress in implementing its
regulatory schedule for the phaseout of ozone-depleting substances
(ODS). The regulatory implementation schedule, which meets domestic
and international deadlines for the phaseout, takes a two-pronged
approach:
. ODS Phaseout. Complete the phaseout of Class I ozone-depleting
substances by the end of 1995, and
. Significant New Alternatives Policy (SNAP). Implement the SNAP,
which evaluates substitutes or alternatives for ozone-depleting
substances based on the ozone-depletion potential of a substance,
global warming potential, flammability, toxicity, exposure potential,
and economic and technical feasibility.
In January 1993 in keeping with the Montreal Protocol and subsequent
agreements, the United States signed a notice of proposed rulemaking
(NPRM). In addition to accelerating the phaseout schedule, the
proposed rule would list methyl bromide as a Class I substance
and freeze its production at 1991 levels.
A labeling requirement for containers of ozone-depleting substances,
for products manufactured with ODS, and for products containing
ODS will go into effect in 1994. The following warning will appear
on labels: -Warning: Contains (insert name of substance), a substance
which harms public health and the environment by destroying ozone
in the upper atmosphere.- The EPA will enforce use of the label.
Studies on CFC replacement compounds are underway to determine
their potential impacts on humans and the environment. The metabolism
and toxicity of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons
(HFCs), for example, are being investigated. Available data indicate
that compounds that are rapidly metabolized are more toxic than
those that are slowly metabolized. HCFC-132b is metabolized rapidly
and yields metabolites that are potent inhibitors of the enzymes
used by the body to detoxify many drugs and chemicals. As a result
its development has been discontinued. Other research suggests
that HCFC-123 may increase susceptibility to hepatitis in sensitive
individuals. Computer modeling studies of reactions of CFC substitutes
are being conducted to develop models that will predict metabolism
rates and identify compounds likely to be poorly metabolized and
therefore of little toxic potential. Preliminary results of this
research are promising, and the range of compounds to be tested
has been expanded. The biospheric transport and fate of CFC substitutes
are also being investigated to assess likely future concentrations
of these new chemicals in air, water bodies, and soils.
Substantial progress has been made in establishing a U.S. Interagency
Ultraviolet (UV) Monitoring Network. Several federal agencies
are either currently operating or are developing UV monitoring
networks. Because each of the individual agencies have different
research and operational needs for UV data (such as concerns with
effects on agriculture, on human health, and on fish and wildlife),
each of these networks are using different types of instruments
that best address their respective needs. A UV monitoring plan
has been developed to ensure that data collected by the individual
agency networks are intercalibrated.
The United States is a major participant in international efforts
to understand and assess the state of knowledge about global change
issues. Hundreds of scientists from more than 50 countries have
participated in recent assessments which have included review
of scientific results, environmental impacts, technologies, and
economic considerations. These intergovernmental assessments are
especially important as they are intended to serve as primary
inputs to the many international conventions and protocols that
the United States supports, including the Framework Convention
on Climate Change, the Montreal Protocol on Ozone, and the Convention
on Biological Diversity (see Chapter 6).
The Intergovernmental Panel on Climate Change (IPCC) was established
by the World Meteorological Organization and the United Nations
Environment Program in 1988. The IPCC produces reports on climate
change which characterize agreement and disagreement within the
climate change research community on issues of importance to policymakers.
The IPCC has produced the 1990 Assessment covering changes in
climate, potential impacts, and response strategies; a 1992 Supplement
which updated the 1990 volume in time for consideration by governments
at the Earth Summit; and a forthcoming 1994 Special Report focusing
on radiative forcing of climate resulting from human emissions
of greenhouse gases. That report also includes technical guidelines
for evaluating sources and sinks of greenhouse gas emissions and
technical guidelines for evaluating the potential impacts of climate
change. The IPCC currently is preparing a second comprehensive
assessment of climate change and the vulnerability of natural
and socioeconomic systems to change, scheduled for completion
in 1995.
The IPCC assessment process has been a critical part of establishing
scientific consensus on climate change issues, largely because
of the extensive involvement of a diversity of national and scientific
backgrounds, representation of minority views, extensive peer
review, and a commitment to scientific excellence.
Clinton, W.J. and A.C. Gore, The Climate Change Action Plan,
(Washington, DC: Executive Office of the President, October 1993).
Executive Office of the President, Office of Science and Technology
Policy, Our Changing Planet: The FY 1995 U.S. Global Change
Research Program, A Report by the Committee on Environment
and Natural Resources Research of the National Science and Technology
Council, (Washington, DC: EOP, OSTP, 1994).
Hickman, L.E. and S.D. Lyles, Sea Level Variation in the United
States, 1855-1993, (Silver Spring, MD: U.S. Department of
Commerce, National Oceanic and Atmospheric Administration, National
Ocean Service, 1994).
Intergovernmental Panel on Climate Change, Radiative Forcing
of Climate Change: The 1994 Report of the Scientific Assessment
Working Group of IPCC, (World Meteorological Organization
and United Nations Environment Program, 1994).
U.S. Congress, Office of Technology Assessment, Combined Summaries:
Technologies to Sustain Tropical Forest Resources and Biological
Diversity, (Washington, DC: GPO, May 1992).
U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, National Environmental Satellite, Data, and Information
Service, National Climatic Data Service, Climate Variations
Bulletin, Historical Climatology Series 4-7, Vol. 5, No. 12
(Asheville, NC: DOC, NOAA, NESDIS, NCDC, December 1993).
Storm Data and Unusual Weather Phenomena with Late Reports
and Corrections, Vol. 35, No. 12 (Asheville, NC: DOC, NOAA,
NESDIS, NCDC, December 1993).
U.S. Department of Energy, Oak Ridge National Laboratory, Carbon
Dioxide Information Analysis Center, Trends -93: A Compendium
of Data on Global Change, (Oak Ridge, TN: DOE, ORNL, CDIAC,
September 1994).
U.S. Department of Energy, Energy Information Administration,
Emissions of Greenhouse Gases in the United States 1985-1990,
(Washington, DC: DOE, EIA, September 1993).
Energy Use and Carbon Emissions: Some International Comparisons,
(Washington, DC: DOE, EIA, March 1994).
U.S. Department of the Interior, United States Geological Survey,
At Work Across the Nation: U.S. Geological Survey Yearbook
Fiscal Year 1993, (Reston, VA: DOI, USGS, 1993).
U.S. Department of State, Climate Action Report, Submission
of the United States of America Under the United Nations Framework
Convention on Climate Change, (Washington, DC: GPO, 1994).
U.S. Department of Transportation and U.S. Environmental Protection
Agency, Clean Air through Transportation: Challenges in Meeting
National Air Quality Standards, (Washington, DC: DOT and EPA,
August 1993).
U.S. Environmental Protection Agency, Office of Air Quality Planning
and Standards, National Air Pollutant Emission Trends,
1900-1992, (Research Triangle Park, NC: EPA, OAQPS, October 1993).
National Air Quality and Emissions Trends Report, 1992,
(Research Triangle Park, NC: EPA, OAQPS, October 1993).
U.S. Environmental Protection Agency, Office of Policy, Planning
and Evaluation, Inventory of U.S. Greenhouse Gas Emissions
and Sinks: 1990-1993, (Washington, DC: EPA, OPPE, September
1994).
Implications of Climate Change for International Agriculture:
Crop Modeling Study, (Washington, DC: EPA, OPPE, June 1994).
U.S. Environmental Protection Agency, Office of Pollution Prevention
and Toxics, 1991 Toxics Release Inventory: Public Data Release,
(Washington, DC: EPA, OPPT, May 1993).
Air Quality
Conditions and Trends
Americans and Their Cars
NAAQS Pollutants
Carbon Monoxide
Air Quality Success Stories
Lead
Nitrogen Dioxide
Ozone
Particulates
Sulfur Dioxide
Air Quality Population Estimates
Smog
Pollution Standards Index (PSI)
Sulfur Dioxide/Nitrogen Dioxide
Program Accomplishments
Motor Vehicle Emissions
Cleaner Fuels
Cleaner Cars, Trucks, and Buses
Inspection and Maintenance
Transportation
Fleet Vehicles
Air Toxics
Indoor Air Quality
Secondhand Smoke
Radon
Sick-Building Syndrome
Asthma and Other Respiratory Problems
Indoor Air Management
EPA Radon Program
Acid Rain and the Clean Air Act
National Trends Network
Acid Rain Program
National Acid Precipitation Assessment Program
Climate
Conditions and Trends
Major U.S. Weather Events
Record Temperature Extremes
Record Precipitation Extremes
Hurricanes
Hurricane Preparedness
Tornadoes
Global Environmental Change
Greenhouse Gases
Ozone
Stratospheric Ozone Depletion
Aerosols
Natural Factors
Climate Change Indicators
Land Use and Global Climate Change
Why is Climate Change an Issue
Program Accomplishments
U.S. Climate Change Programs
Earth Day 1993
The Climate Change Action Plan
White House Conference on Global Climate Change
Green Technology
Phaseout of Ozone-Depleting Substances
Freezing Methyl Bromide Production
ODS Labeling Program
CFC Replacements
UV Monitoring Network
International Climate Change Actions
The Intergovernmental Panel on Climate Change
REFERENCES
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