£EPA
United States
Environmental Protection
Agency
National Air Quality
STATUS AND TRENDS THROUGH 2007
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Printed on 100% recycled/recyciable process chlorine-free paper with 100% post-consumer fiber using vegetabie-oii-based ink.
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National Air Quality
STATUS AND TRENDS THROUGH 2007
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Air Quality Assessment Division
Research Triangle Park, North Carolina
EPA-454/R-08-006
November 2008
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Highlights
Air Pollution
Six Common Pollutants
Ground-Level Ozone
Particle Pollution
Lead
Nitrogen Dioxide
Carbon Monoxide
Sulfur Dioxide
Toxic Air Pollutants
Atmospheric Deposition
Visibility in Scenic Areas
Climate Change and Air Quality
International Transport of Air Pollution
Terminology
WebSites
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HIGHLIGHTS
This summary report highlights EPA's most recent
evaluation of the status and trends in our nation's air
quality.
LEVELS OF SIX COMMON POLLUTANTS
CONTINUE TO DECLINE
• Cleaner cars, industries, and consumer products
have contributed to cleaner air for much of the U.S.
• Since 1990, nationwide air quality for six air
pollutants for which there are national standards
has improved significantly. These air pollutants are
ground-level ozone (O3), particle pollution (PM2 5
and PM10), lead (Pb), nitrogen dioxide (NO2), carbon
monoxide (CO), and sulfur dioxide (SO2). Nationally,
air pollution was lower in 2007 than 1990 for:
- 8-hour ozone, by 9 percent
- annual PM2 5 (since 2000), by 11 percent
- PM10, by 28 percent
- Lead, by 80 percent
- NO2, by 35 percent
- 8-hour CO, by 67 percent
- SO2, by 54 percent
• Despite clean air progress, in 2007,158.5 million
people lived in counties that exceeded any national
Ozone (8-hour)
PM26 (annual and 24-hour)
PM,0
Lead
CO -
SOj (annual and 24-hour) -
Any NAAQS -
13.0
4.5
0.0
0.0
0.0
ambient air quality standard (NAAQS). Ground-
level ozone and particle pollution still present
challenges in many areas of the country.
• Though PM2 5 concentrations were higher in 2007
than in 2006, partly due to weather conditions,
annual PM2 5 concentrations were nine percent
lower in 2007 than in 2001.
• 8-hour ozone concentrations were five percent
lower in 2007 than in 2001. Ozone levels did not
improve in much of the East until 2002, after
which there was a significant decline. This decline
is largely due to reductions in oxides of nitrogen
(NOJ emissions required by EPA's rule to reduce
ozone in the East, the NOx SIP Call. EPA tracks
progress toward meeting these reductions through
its NOx Budget Trading Program.
LEVELS OF MANY TOXIC AIR POLLUTANTS
HAVE DECLINED
• In 2007, 27 National Air Toxics Trends Stations
(NATTS) were fully operational, providing a
consistent long-term national network operated by
state and local agencies with coordination provided
by EPA.
144.8
73.4
158.5
I I I I I I I ' I
0 20 40 60 80 100 120 140 160 180
Millions of People
Number of people living in counties with air quality concentrations above the level of the primary (health-based) National
Ambient Air Quality Standards (NAAQS) in 2007.
Note: In 2008, EPA strengthened the national standard for 8-hour ozone to 0.075 ppm and the national standard for lead to 0.15 |ag/m3. This figure
includes people living in counties that monitored ozone and lead concentrations above the new levels. PM25 are particles less than or equal to
2.5 micrometers (|am) in diameter. PM10 are particles less than or equal to 10 |am in diameter.
NATIONAL AIR QUALITY STATUS AND TRENDS
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HIGHLIGHTS
2005 Population per Square Mile
in Counties above any NAAQS in 2007
0-25
26-75
^B 76-250
^B 250-500
^H >500
'-w
Alaska
Puerto Rico
Population density (2005 population per square mile) in counties with air quality concentrations above the
level of any of the primary NAAQS in 2007.
Note: This figure includes counties that monitored ozone and lead concentrations above the new levels set in 2008.
• Toxic hydrocarbons such as benzene, 1,3-butadiene,
styrene, xylenes, and toluene decreased by
5 percent or more per year between 2000 and
2005 at more than half of ambient monitoring
sites. Other key contributors to cancer risk, such
as carbon tetrachloride, tetrachloroethylene, and
1,4-dichlorobenzene, declined at most sites.
• Control programs for mobile sources and facilities
such as chemical plants, dry cleaners, coke ovens,
and incinerators are primarily responsible for
reductions in toxic air pollutant emissions between
2000 and 2005. These emissions reductions have
contributed to reductions in cancer risk as well as
reductions in the hydrocarbon contribution to ozone
concentrations.
ACID RAIN AND HAZE ARE DECLINING
• EPA's NOx SIP Call and Acid Rain Program have
contributed to significant improvements in air
quality and environmental health. The required
reductions in sulfur dioxide and nitrogen oxides
have led to significant decreases in atmospheric
deposition, contributing to improved water quality
in lakes and streams. For example, between the
1989-1991 and 2005-2007 time periods, wet sulfate
deposition and wet nitrate deposition decreased
more than 30 percent in parts of the East.
• Between 1996 and 2006, visibility in scenic areas
has improved throughout the country. Five
areas—Mt. Rainier National Park, Wash.; Great
Smoky Mountains National Park, Tenn.; Great Gulf
Wilderness, N.H.; Canyonlands National Park,
Utah; and Snoqualmie Pass, Wash. — show notable
improvement on days with the worst visibility.
CLIMATE CHANGE AND INTERNATIONAL
TRANSPORT: IMPROVING OUR
UNDERSTANDING
• The U.N. Intergovernmental Panel on Climate
Change concluded climate change is evident from
observations of increases in global average air and
ocean temperatures, widespread melting of snow
and ice, and rising global average sea level.
• Research is under way to examine and improve our
understanding of the links between air quality and
climate: how a warming climate could affect air
quality and how air quality could affect climate.
• Researchers also are improving our understanding
about how pollution moves between countries and
continents.
NATIONAL AIR QUALITY STATUS AND TRENDS
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Sources-to-Effects Continuum
EMISSIONS
MONITORING
DOSAGE
ATMOSPHERIC
CHEMISTRY/
TRANSPORT
HEALTH EFFECTS &
ENVIRONMENTAL
IMPACTS
Because air pollution harms human health and damages the environment, EPA tracks pollutant emissions. Air pollutants are
emitted from a variety of sources including stationary fuel combustion, industrial processes, highway vehicles, and non-road
sources. These pollutants react in and are transported through the atmosphere. EPA, other federal agencies, and state, local,
and tribal agencies monitor air quality at locations throughout the U.S. Data collected through ambient monitoring are used
in models to estimate population exposure. Personal health monitoring is conducted via special studies to better understand
actual dosage of pollutants. EPA uses monitoring data, population exposure estimates, and personal dosage data to better
understand health effects and environmental impacts of air pollutants.
MORE IMPROVEMENTS ANTICIPATED
• EPA expects air quality to continue to improve
as recent regulations are fully implemented and
states work to meet national standards. Among
these regulations are: the Locomotive Engines and
Marine Compression - Ignition Engines Rule, the
Tier II Vehicle and Gasoline Sulfur Rule, the Heavy-
Duty Highway Diesel Rule, the Clean Air Non-road
Diesel Rule, and the Mobile Source Air Toxics Rule.
NATIONAL AIR QUALITY STATUS AND TRENDS
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AIR POLLUTION
HEALTH AND ENVIRONMENTAL IMPACTS
Air pollution can affect our health in many ways.
Numerous scientific studies have linked air pollution to
a variety of health problems including (1) aggravation
of respiratory and cardiovascular disease (as indicated
by increased emergency department visits and
hospital admissions); (2) decreased lung function
and increased frequency and severity of respiratory
symptoms such as difficulty breathing and coughing;
(3) increased susceptibility to respiratory infections;
(4) effects on the nervous system, including the brain,
such as IQ loss and impacts on learning, memory, and
behavior; (5) cancer; and (6) premature death. Some
sensitive individuals appear to be at greater risk for
air pollution-related health effects, for example, those
with pre-existing heart and lung diseases (e.g., asthma,
emphysema, and chronic bronchitis), diabetics, older
adults, and children. In 2007,158.5 million people lived
in counties that exceeded national air quality standards.
Air pollution also damages our environment. Ozone
can damage vegetation including adversely impacting
the growth of trees and reducing crop yields. Visibility
is reduced by particle pollutants that scatter and absorb
light. Typical visual range in the eastern U.S. is 15 to
30 miles, approximately one-third of what it would
be without man-made air pollution. In the West, the
typical visual range is about 60 to 90 miles, or about
one-half of the visual range under natural conditions.
Pollution in the form of acids and acid-forming
compounds (such as sulfur dioxide [SO2] and oxides of
nitrogen [NOJ) can deposit from the atmosphere to the
Earth's surface. This is called acid deposition and can
be either dry or wet. Wet deposition is more commonly
known as acid rain. Acid rain can occur anywhere
and, in some areas, rain can be 100 times more acidic
than natural precipitation. Acid deposition can be a
very serious regional problem, particularly in areas
downwind from high SO2 and NOx emitting sources,
e.g., coal burning power plants, smelters, and factories.
Acid deposition can have many harmful ecological
effects in both land and water systems. While acid
deposition can damage tree foliage directly, it more
commonly stresses trees by changing the chemical
and physical characteristics of the soil. In lakes, acid
deposition can kill fish and other aquatic life.
The burning of fossil fuels, such as coal and oil, and
deforestation can cause concentrations of heat-trapping
"greenhouse gases" to increase significantly in our
atmosphere. These gases prevent heat from escaping to
space, somewhat like the glass panels of a greenhouse.
Greenhouse gases are necessary to life as we know it,
because they keep the planet's surface warmer than
it would otherwise be. But, as the concentrations of
these gases continue to increase in the atmosphere,
the Earth's temperature is climbing above past levels.
Studies show that growth in greenhouse gases and
associated changes in weather conditions may increase
current air pollution levels.
Air Pollution and Health/Welfare Effects - Improving Our Knowledge
Air pollution continues to have adverse impacts on the human and environmental health of the United States, despite clear
evidence that overall air quality has improved. EPA's research program is evolving with growing emphasis on the development
of a multi-pollutant approach for assessing the impacts of air pollution. Critical components of this research will inform
our understanding of how pollutants from sources impact ambient air concentrations, how these concentrations relate to
exposures, and, in turn, how exposures relate to health and welfare outcomes. Some highlights of current air pollution research
activities include:
• EPA-funded Particulate Matter Research Centers are conducting cutting-edge research to improve our understanding
of how particle pollution affects human health and the sources of particles most responsible for these effects. Research
grants focus high-priority issues including human susceptibility, mechanisms of health effects, exposure-response
relationships, and the cross-cutting issue of linking health effects with particle pollution sources and components.
• The Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air) is investigating the impact of air pollution on
the progression of cardiovascular disease among more than 7,000 participants with diverse backgrounds from nine
locations. The study will help evaluate if cardiac disease is accelerated by exposure to particle pollution in combination
with gaseous pollutants and if some ethnic populations are more susceptible to effects associated with these exposures.
• The Health Effects Institute's National Particle Components Toxicity (NPACT) Initiative will build upon the existing scientific
foundation for particles to improve our understanding of the toxicity of specific components and characteristics of
particle pollution (and ultimately sources of these components).
NATIONAL AIR QUALITY STATUS AND TRENDS
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ir Pollution Sources, Health Effects, and Environmental
Ozone (OJ
Particles
Lead
Sources
Secondary pollutant formed by
chemical reaction of VOCs and
NOx in the presence of sunlight.
Emitted or formed through
chemical reactions (e.g., NOx,
SO2, NH3); fuel combustion (e.g.,
burning coal, wood, diesel);
industrial processes; agriculture
(plowing, field burning); and
unpaved roads.
Smelters (metal refineries)
and other metal industries;
combustion of leaded gasoline
in piston engine aircraft; waste
incinerators; and battery
manufacturing.
Health Effects
Aggravation of respiratory and
cardiovascular disease, decreased
lung function and increased
respiratory symptoms, increased
susceptibility to respiratory infection,
and premature death.
Aggravation of respiratory and
cardiovascular disease, reduced
lung function, increased respiratory
symptoms, and premature death.
Damage to developing nervous
system, resulting in IQ loss and
impacts on learning, memory, and
behavior in children. Cardiovascular
and kidney effects in adults and early
effects related to anemia.
Environmental Effects
Fuel combustion (especially high-
Sulfur Dioxide sulfur coal); electric utilities and
(SO2) industrial processes; and natural
sources such as volcanoes.
Oxides of
Nitrogen
(N0x)
Carbon
Monoxide
(CO)
Fuel combustion (e.g., electric
utilities, industrial boilers, and
vehicles) and wood burning.
Fuel combustion (especially
vehicles).
Aggravation of asthma and
increased respiratory symptoms.
Contributes to particle formation with
associated health effects.
Aggravation of respiratory disease
and increased susceptibility to
respiratory infections. Contributes to
ozone and particle formation with
associated health effects.
Reduces the ability of blood to carry
oxygen to body tissues including
vital organs. Aggravation of
cardiovascular disease.
Damage to vegetation such as
impacts on tree growth and reduced
crop yields.
Impairment of visibility, effects
on climate, and damage and/
or discoloration of structures and
property.
Harm to environment and wildlife.
Contributes to the acidification of
soil and surface water and mercury
methylation in wetland areas.
Contributes to particle formation with
associated environmental effects.
Contributes to the acidification and
nutrient enrichment (eutrophication,
nitrogen saturation) of soil and surface
water. Contributes to ozone and
particle formation with associated
environmental effects.
None known.
Ammonia
(NH3)
Volatile
Organic
Compounds
(VOCs)
Mercury
Livestock agriculture (i.e., raising/
maintaining livestock for milk,
meat, and egg production);
fertilizer application.
Fuel combustion and
evaporation (especially vehicles);
solvents; paint; and natural
sources such as trees and
vegetation.
Fuel combustion (especially
coal-fired power plants); waste
disposal; industrial processes;
mining; and natural sources
(volcanoes and evaporation
from enriched soil, wetlands, and
oceans).
Contributes to particle formation with
associated health effects.
Cancer (from some toxic air
pollutants) and other serious health
problems. Contributes to ozone
formation with associated health
effects.
Liver, kidney, and brain damage; and
neurological and developmental
damage.
Contributes to eutrophication
of surface water and nitrate
contamination of ground water.
Contributes to particle formation with
associated environmental effects.
Contributes to ozone formation with
associated environmental effects.
Deposition into rivers, lakes, and
oceans accumulates in fish resulting in
exposure to humans and wildlife.
Fuel combustion (including
Other Toxic particle and gaseous emissions);
Air Pollutants vehicles; industrial processes;
building materials; and solvents.
Cancer, immune system damage,
neurological, reproductive,
developmental, respiratory, and
other health problems. Some toxic air
pollutants contribute to ozone and
particle pollution with associated
health effects.
Harmful to wildlife and livestock.
Some toxic air pollutants accumulate
in the food chain. Some toxic air
pollutants contribute to ozone and
particle pollution with associated
environmental effects.
NATIONAL AIR QUALITY STATUS AND TRENDS
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AIR POLLUTION
SOURCES OF AIR POLLUTION
Air pollution consists of gas and particle contaminants
(PM2 5 and PM10) that are present in the atmosphere.
Gaseous pollutants include SO2, NOx, ozone (O3),
carbon monoxide (CO), volatile organic compounds
(VOCs), certain toxic air pollutants, and some gaseous
forms of metals. Particle pollution includes a mixture
of compounds. The majority of these compounds can
be grouped into four categories: sulfates, nitrates,
elemental carbon, organic carbon, and "crustaT
material.
Some pollutants are compounds that are released
directly into the atmosphere. These include gases
such as SO2 and some particles, such as soil and soot.
Other pollutants are formed in the air. Ground-level
ozone forms when emissions of NOx and VOCs react
in the presence of sunlight. Similarly, some particles
are formed. For example, particle sulfates are the
product of SO2 and ammonia (NH3) gases reacting in
the atmosphere. Weather plays an important role in
the formation of air pollutants, as discussed later in the
ozone and particle pollution sections.
EPA tracks direct emissions of air pollutants and
emissions that contribute to air pollution formation,
also known as precursor emissions. Emissions data are
compiled from many different organizations, including
industry and state, tribal, and local agencies. Some
emissions data are based on actual measurements
while others are estimates.
Emissions, in general, are emitted from large stationary
fuel combustion sources (such as electric utilities and
industrial boilers), industrial and other processes (such
as metal smelters, petroleum refineries, manufacturing
facilities, and solvent utilization), and mobile sources
including highway vehicles and non-road sources
(such as mobile equipment, marine vessels, aircraft,
and locomotives). Sources emit different combinations
of pollutants. For example, electric utilities release SO2,
NOx, and particles. Figure 1 shows the distribution of
national total emissions estimates by source category
for specific pollutants for 2007. Highway vehicles
and non-road mobile sources together contribute
approximately three-fourths of national CO emissions.
Electric utilities contribute about 70 percent of
national SO2 emissions. Agricultural operations (other
processes) contribute nearly 80 percent of national
NH3 emissions. Almost 50 percent of the national VOC
emissions are coming from highway vehicles and
solvent use (other processes). Pollutant levels differ
across regions of the country and within local areas,
both urban and rural, depending on the size and type
of sources present.
The Clean Air Act and EPA have established a
list of 187 air toxics (also known as hazardous air
pollutants—HAPs). These pollutants are known
or are suspected of causing serious health effects,
such as cancer, birth defects, or reproductive effects.
Many of the VOCs (e.g., benzene, 1,3-butadiene, and
chloroform) and particles (e.g., arsenic, lead, and
manganese) are toxic air pollutants, as shown in Figure
2.
A number of sources (e.g., stationary fuel combustion,
industrial processes, mobile sources) emit both particle
and gaseous toxic air pollutants that contribute to
both ozone and particle formation. For example, diesel
exhaust contains particles as well as VOCs, some of
which are toxic.
Direct PM
Direct PM
20
40 60
Percent of Emissions
80
Source Category
Stationary Industrial and
Fuel Combustion Other Processes
Highway
Vehicles
Non-Road
Mobile
Figure 1. Distribution of national total emissions by source category for specific pollutants, 2007.
NATIONAL AIR QUALITY STATUS AND TRENDS
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Most toxic air pollutants come from a variety of
source types. For example, though most benzene
emissions are from highway vehicles, benzene is
also emitted by some stationary fuel combustion,
industrial, and non-road mobile sources.
Control programs that target specific source
types can provide multiple benefits. For
example, lowering VOC emissions from vehicle
sources reduces toxic air pollutant levels and
also reduces VOCs that contribute to ozone
formation. Lowering NOx emissions from
electric utilities and industrial boilers reduces
the NOx contribution to both ozone and nitrate
particle formation, both of which contribute to
smog and reduced visibility.
Energy production and transportation sources
contribute to CO2, VOC, SO2, and NOx emissions
which affect greenhouse gases and the formation
of ozone and particle pollution. Reducing energy
consumption and vehicle use, or converting
to alternative or more efficient energy sources
will improve health protection and reduce
environmental effects.
Figure 2. Distribution of national total emissions by
source category for individual urban toxic air pollutants
and diesel particle pollution, 2005.
Note: Contributions of aldehyde emissions (formaldehyde
and acetaldehyde) are for primary direct emissions and do not
include secondary aldehydes formed via photochemical reactions.
Contributions from fires are not included. In 2005, fires contributed
roughly 35 percent of the polycyclic organic matter, 15 percent
of the benzene, 37 percent of the 1,3-butadiene, 50 percent of the
formaldehyde, 67 percent of the acrolein, and 24 percent of the
acetaldehyde.
Acrylonitrile
Benzene
1,3-Butadiene
Carbon Tetrachloride
Chloroform
1,2-Dichloropropane
1,3-Dichloropropene
Ethylene Dibromide
Ethylene Dichloride
Ethylene Oxide
Methylene Chloride
Perchloroethylene
1,1,2.2-Tetrachloroethane
Trichloroethylene
Vinyl Chloride
Arsenic Compounds
Beryllium Compounds
Cadmium Compounds
Chromium Compounds
Lead Compounds
Manganese Compounds
Mercury Compounds
Nickel Compounds
Acetaldehyde
Acrolein
Formaldehyde
Coke Oven Emissions
Hexachlorobenzene
Hydrazine
PCBs
Polycylic Organic Matter
Quinoline
Diesel Particulate
VOCs
Metals
Carbonyls
Other VOCs
Diesel Exhaust
20 40 60 80
Percent of Emissions
100
Stationary Industrial and Highway Non-Road
Fuel Other Vehicles Mobile
Combustion Processes
Emissions Included in this Report
PM emissions are directly emitted particles only. They do not
include gaseous emissions that condense in cooler air (i.e.,
condensibles) or emissions from fires and resuspended dust.
SO2, NOx, VOC, CO, and lead emissions are from human
activity sources only.
NH3 emissions are primarily from animal livestock operations
and are estimated using population data (e.g., cattle, cows,
pigs, poultry) and management practices.
2007 emissions were derived from the 2005 emissions
inventory, except for SO2 and NOx emissions, which were
derived from measured data from electric utilities.
Highway vehicle emissions were based on emission
measurements from vehicle testing programs.
Emissions data were compiled using the best methods and
measurements available at the time.
NATIONAL AIR QUALITY STATUS AND TRENDS
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AIR POLLUTION
TRACKING POLLUTANT
EMISSIONS
Since 1990, air pollutant
emissions have declined, with the
greatest percentage drop in lead
emissions. The removal of lead
from gasoline used in highway
vehicles is primarily responsible
for the 72 percent decrease in lead
emissions. NH3 shows the least
percentage drop, four percent.
While PM2 5 emissions have declined
by over one half, PM10, NOx, and
VOC emissions have declined by
around one third, and SO2 and CO
emissions have declined by more
than one-third, as shown in Table 1.
Table 1. Change in annual national emissions
per source category (1990 vs. 2007) (thousand tons).
Source Category
Stationary Fuel
Combustion
Industrial and
Other Processes
Highway Vehicles
Non-road Mobile
Total Change
(thousand tons)
Percent Change
(1990 vs. 2007)
PM25
-693
-224
-223
-49
-1189
-51%
PM10
-722
-43
-235
-62
-1062
-33%
NH3
+40
-353
+ 152
-28
-189
-4%
S02
-9036
-844
-412
-25
-10267
-45%
NOx
-4894
+229
-4029
+383
-8311
-33%
VOC
+621
-2809
-5786
-12
-7986
-35%
CO
-207
+8442
-68645
-2685
-63095
-44%
Pb
-0.410
-2.621
-0.421
-0.153
-3.604
-72%
Note: Lead (Pb) emission changes are from 1990 to 2002.
The combined emissions of the six common pollutants (PM25, SO2, NOx, VOCs, CO, and lead) dropped 41 percent
since 1990, as shown in Figure 3. This progress has occurred while the U.S. economy continued to grow, Americans
drove more miles, and population and energy use increased. These emissions reductions resulted from a variety of
control programs through regulations and through voluntary partnerships between federal, state, local, and tribal
governments; academia; industrial groups; and environmental organizations.
ross Domestic Product
95 96 97 98 99 00 01 02 03 04 05 06 07
Figure 3. Comparison of growth measures and emissions, 1990-2007.
Note: The U.S. Department of Transportation's Federal Highway Administration reports that cumulative travel for January-April
2008 is down by 2.1 percent compared to the same period in 2007.
NATIONAL AIR QUALITY STATUS AND TRENDS
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Emissions Where You Live
To get emissions information at a state or local level, visit http://www.epa.gov/air/emissions/where.htm. Here you can find
emissions totals for a state or county grouped by major source types, or select Google Earth to see nearby sources of emissions.
Zoom to the area of interest, tilt the map to see emissions levels, select a site for facility information, or zoom closer for an aerial
photo.
Zoom to Atlanta
Tilt to see emissions levels
Select a site
Georgia Power Company Bowen Steam-Electric Generator
317 Covered Bridge Road Cartereville GA 30120
SIC. 4911
Electric. Gas and Sanitary Services Electric Services Electric Services
NAICS:
Annual Air Emissions
Cartoon Monoxide 2002 |
Nitrogen Oxide 2002 1
Paniculate Matter 10 2002 1
Paniculate Matter 2 5 2002 1
Sulfur Dioxide 2002 1
Volilile Organic Compounds 2002
Emissions Amount
2125
37302
11985
9027
160673
297
0 100000 200000
Tons
As o( May 2008
NATIONAL AIR QUALITY STATUS AND TRENDS
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SIX COMMON
POLLUTANTS
To protect public health and the environment, EPA has
established, and regularly reviews, national air quality
standards for six common air pollutants also known
as "criteria" pollutants: ground-level ozone, particle
pollution (PM2 5 and PM10), lead, nitrogen dioxide
(NO2), carbon monoxide (CO), and sulfur dioxide (SO2).
TRENDS IN NATIONAL AIR QUALITY
CONCENTRATIONS
Air quality is measured by monitors located across
the country. Monitored levels of the six common
pollutants show improvement since the Clean Air Act
was amended in 1990. Figure 4 shows national trends
between 1990 and 2007 in the common pollutants
relative to their air quality standards. Most pollutants
show a steady decline throughout the time period.
Lead declined in the 1990s as control programs were
implemented to lower concentrations in areas above
the national standard. In general, lead concentrations
have remained low since 2002. Large year-to-year
changes shown in lead concentrations reflect the
influence of emissions changes due to operating
schedules or other facility activities, such as plant
closings, on measurements at nearby monitors. Ozone
and PM2 5 trends are not smooth and show year-to-year
influences of weather conditions which contribute to
their formation, dispersion, and removal from the air.
Ozone was generally level in the 1990s, and showed
a notable decline after 2002 mostly due to oxides of
nitrogen (NOx) emission reductions in the East.
Many areas still have air quality problems caused by
one or more pollutant. Ozone and particle pollution
continue to present air quality challenges throughout
much of the U.S., with many monitors measuring
concentrations above, or close to, national air quality
standards.
400% -
200% :
Ozone, 568 sites (4th maximum 8-hour average)
PM;s, 718 sites (24-hour average)
PM;S, 718 sites (annual average)
PMI0. 360 sites (2"a maximum 24-hour average)
Lead, 72 sites (maximum 3-month average)
NO;. 160 sites (annual average)
CO, 229 sites (2nc maximum 8-hour average)
SO,, 281 sites (annual average)
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07
Figure 4. Comparison of national levels of the six common pollutants to national ambient air quality standards,
1990-2007. National levels are averages across all sites with complete data for the time period.
Note: Air quality data for PM25 start in 1999. Trends from 2001 though 2007 (using the larger number of monitors operating since
2001) are the focus of graphics in the following sections.
Environmental Justice
Environmental justice is the fair treatment and meaningful involvement of all people regardless
of race, color, national origin, or income with respect to the development, implementation,
and enforcement of environmental laws. EPA's Office of Air and Radiation (OAR) is committed
to promoting and supporting environmental justice. For more information about EPA OAR's
environmental justice program and air issues, visit http://www.epa.gov/air/ej/.
1 0
NATIONAL AIR QUALITY STATUS AND TRENDS
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TRENDS IN "UNHEALTHY" AIR QUALITY DAYS
The Air Quality Index (AQI) relates daily air pollution
concentrations for ozone, particles, NO2, CO, and SO2
to health concerns for the general public. A value of
100 generally corresponds to the national air quality
standard for each pollutant. Values below 100 are
generally thought of as satisfactory. Values above 100
are considered to be unhealthy—at first for certain
sensitive groups of people, then for everyone as the
AQI values increase.
Figure 5 shows the number of unhealthy days that
selected metropolitan areas experienced in 2001-
2007. Most areas had fewer unhealthy days in 2007
compared to 2001 or 2002. However, Los Angeles,
Salt Lake City, and many cities in the east had more
unhealthy days in 2007 than in 2006. Nearly all of
EPA's Air Quality Index (AQI)
Air Quality Index Levels of Health Concern
(AQI) Values
0 to 50 Good
51-100 Moderate
101-150 Unhealthy for Sensitive Groups
AIR QUALITY INDEX
the increases in unhealthy days in the east are due to
ozone and/or particle pollution. Weather conditions,
as well as emissions, contribute to ozone and particle
pollution formation.
2001 2002 2003 2004 2005 2006 2007
Figure 5. Number of days reaching Unhealthy for Sensitive Groups on the Air Quality Index for 2001-2007 at
selected cities.
Note: The AQI breakpoints reflect the new primary standard for 8-hour ozone set in 2008.
NATIONAL AIR QUALITY STATUS AND TRENDS
1 1
-------
SIX COMMON POLLUTANTS
Review of the National Ambient Air Quality Standards (NAAQS)
The Clean Air Act requires EPA to set two types of NAAQS for the common air pollutants:
• primary standards to protect public health with an adequate margin of safety, including the health of sensitive
populations such as asthmatics, children, and the elderly; and
• secondary standards to protect public welfare from adverse effects, including visibility impairment and effects on the
environment (e.g., vegetation, soils, water, and wildlife).
The Clean Air Act requires periodic review of the "standards" and the science upon which they are based. The current
standards and the status of each review are shown below.
Pollutant
Ozone
Lead
N02
S02
PM25
PM,0
CO
Primary Standard(s)
0.075 ppm (8-hour)
0.15 u.g/m3 (3-month)
0.053 ppm (annual)
0.03 ppm (annual)
0.1 4 ppm (24-hour)
15 u.g/m3 (annual)
35 u.g/m3 (24-hour)
150 u.g/m3 (24-hour)
9 ppm (8-hour)
35 ppm (1-hour)
Secondary Standard(s)
Same as Primary
Same as Primary
Same as Primary
0.5 ppm (3-hour)
Same as Primary
Same as Primary
None; no evidence of
adverse welfare effects at
current ambient levels
Status of Review
Review completed 2008; the previous 0.08 ppm
standard remains in effect
Review completed 2008; the previous 1 .5 u.g/m3
standard remains in effect
Primary standard review to be completed 2009;
secondary standard review of SO2 and NO2 to be
completed 2010
Primary standard review to be completed 201 0;
secondary standard review of SO2 and NO2to be
completed 2010
To be completed 201 1
To be completed 201 1
Units of measure are parts per million (ppm) or micrograms per cubic meter of air (u.g/m3). For more information about
the standards, visit http://www.epa.gov/air/criteria.html.
The Air Quality Management Process
Establish
Air Quality
Goals
f
Determine
Emissions
Reductions
\
Track and
Evaluate Progress
Develop Emissions
Reduction Programs
Implement
Programs
Each time EPA establishes air quality goals necessary
to protect public health and the environment, it sets in
motion a chain of events. States and local agencies work
with EPA to:
• identify emissions reductions needed to achieve air
quality goals
• develop emissions reduction programs
• implement emissions reduction strategies and
enforcement activities
• track and evaluate progress
1 2
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
AIR QUALITY IN NONATTAINMENT AREAS
Many areas of the country where air pollution levels
have exceeded the NAAQS have been designated
"nonattainment." Under the Clean Air Act, EPA and
state, tribal, and local air quality planning agencies
work together to develop plans to address air pollution
in these areas. Each year, EPA tracks air quality
progress in areas identified as nonattainment by
reviewing changes in measured concentrations with
respect to the standards. Figure 6 shows which of these
areas are above or below one or more of the standards
as of 2007.
Air quality has improved in the areas that were
designated nonattainment across all six common
pollutants. All of the areas designated as
nonattainment for CO, SO2, and NO2 had air quality
levels below their respective standards as of December
2007. Only one of the nonattainment areas was above
the standard for lead (1.5 |jg/m3)—Herculaneum,
Mo. For ozone, annual PM25, and PM10, a number of
areas were above the standards: 51, 32, and 17 areas,
respectively. Even though many areas were still above
the standard in 2007, there have been improvements
in the concentration levels in the nonattainment areas.
For example, the ozone areas showed a 9 percent
improvement, and the annual PM2 5 areas showed
a 6 percent improvement between the time of
designation and 2007.
•g- 0.1
g 0.095
o> 0.09
1 °-085
O 0.08
sr- 21
ra 19
~S 17
I 15
^ 750
3 550
s 350 I
Air Quality Trends in Nonattainment Areas Above the NAAQS in 2007
Q- ISO
32 areas
17 areas
O
O
_ Number of
Common , .
_ .. , Nonattainment
Pollutants
Areas
^^^^^^P
Ozone
PM25
PM,0
Lead
CO
S02
NO0
126
39
87
13
43
54
1
Year
Designated
TIH^
2004
2005
1990
1991
1991
1990
1990
Nonattainment
Areas Above
NAAQS Level
in 2007
51
32
17
1
0
| |Above NAAQS
I I Below NAAQS
Puerto Rico
Figure 6. Status of original nonattainment areas for one or more standards (i.e., 8-hour ozone, maximum quarterly lead,
annual PM25, 24-hour PMW, annual NO2, 8-hour CO, and annual SO^ as of 2007.
Notes: Designations for the recently revised standards for ozone (2008), lead (2008), and 24-hour PM25 (2006) are to be determined.
Depending on the form of the standard, a single year or an average of multiple years of data is compared with the level of the standard.
For information about air quality standards, visit http://www.epa.gov/air criteria.html. For information about air trends design values,
visit http://www.epa.gov/air/airtrends/values.html.
NATIONAL AIR QUALITY STATUS AND TRENDS
1 3
-------
I
GROUND-LEVEL
OZONE
TRENDS IN OZONE
CONCENTRATIONS
Nationally, ozone concentrations were
5 percent lower in 2007 than in 2001, as
shown in Figure 7. The trend showed
a notable decline after 2002. Though
concentrations in 2007 were among the
lowest since 2002, many areas measured
concentrations above the 2008 national
Figure 7. National 8-hour ozone air
quality trend, 2001-2007 (average of
annual fourth highest daily maximum
8-hour concentrations).
£ a1-
Q_
& 0.08 -
o
|j 0.06-
§ 0.04-
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n -
Averaqe 1(^13 sites
I 90 percent of sites are below this line.
I
1
National Standard
I
10 percent of sites are below this line.
01 02 03 04 05
2001 to 2007: 5% decrease
06
07
Change in Concentration (ppm)
O Increase of 0.006 to 0.020 (30 Sites)
o Little Change +- 0.005 (474 Sites)
O Decrease of 0.006 to 0.020 (423 Sites)
O Decrease of more than 0.020 (4 Sites)
Alaska
Puerto Rico
Figure 8. Change in ozone concentrations in ppm, 2001-2003 vs. 2005-2007 (3-year
average of annual fourth highest daily maximum 8-hour concentrations).
air quality standard for ozone
(0.075 ppm). When comparing
two 3-year periods, 2001-2003 and
2005-2007, 97 percent of the sites
show a decline or little change in
ozone concentrations as shown in
Figure 8. The sites that showed the
greatest improvement were in or
near the following metropolitan
areas: Cleveland, Ohio; parts of
Houston, Texas; Fresno, Calif.;
and Chambersburg, Pa. However,
other parts of Houston also
showed a notable increase.
Thirty sites showed an increase
of greater than 0.005 ppm. Of the
30 sites that showed an increase,
12 had air quality concentrations
below the level of the 2008 ozone
standard for the most recent year
of data, 2007. The remaining
18 sites with concentrations
EPA Strengthens Ground-level Ozone Standards
On March 12, 2008, EPA strengthened the primary and secondary National Ambient Air Quality Standards
for 8-hour ozone to 0.075 ppm. The new standards are tighter than the previous level of 0.08 ppm (effectively
0.084 ppm). The new standards will improve both public health protection and the protection of sensitive trees
and plants. Improved health protection includes preventing cases of reduced lung function and respiratory
symptoms, acute bronchitis, aggravated asthma, doctor visits, emergency department visits and hospital
admissions for individuals with respiratory disease, and premature death in people with heart and lung disease.
The Air Quality Index (AQI) breakpoints were changed to re ect the new primary standard. The new 100 AQI level
for 8-hour ozone is 0.075 ppm. Information on the AQI can be found at http://www.airnow.gov.
1 4
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
Concentration Range (ppm)
• 0.029 - 0.059 (79 Sites)
O 0.060 - 0.075 (427 Sites)
O 0.076 - 0.095 (657 Sites)
• 0.096-0.126 (27 Sites)
Puerto Rico
Figure 9. Ozone concentrations in ppm, 2007 (fourth highest daily maximum
8-hour concentration).
above the new ozone standard
in 2007 were located in or near
the following metropolitan areas:
Birmingham, Ala.; El Centre,
Calif.; Los Angeles, Calif.;
Jacksonville, Fla.; Orlando, Fla.;
Columbus, Ga.; Atlanta, Ga.;
Baton Rouge, La.; New York,
N.Y.; and Houston, Texas. Ozone
trends can vary locally, as shown
by the presence of increases and
decreases at nearby sites.
Figure 9 shows a snapshot
of ozone concentrations in
2007. The highest ozone
concentrations were located in
California, Connecticut, Georgia,
Massachusetts, North Carolina,
and Pennsylvania. Fifty-seven
percent of the sites were above
0.075 ppm, the level of the 2008
standard.
EPA Reviews Ozone Monitoring Requirements
EPA is currently reviewing the requirements for ozone monitoring by state and local air agencies. At present, there are about
1200 ozone monitors in operation, mostly in cities with population over 350,000. EPA is reviewing the following aspects of the
ozone monitoring program:
• The number of monitors required in smaller cities.
• The number and location of monitors required in rural areas, especially near parks and protected areas.
• The number of months of the year when ozone data must be collected and recorded.
High concentrations of ozone
typically occur during months
with warm temperatures and
strong sunlight. Therefore,
year-round monitoring has
not been required except in
certain areas (see map). Some
states monitor in additional
months on a voluntary basis.
EPA is considering extending
the currently required
monitoring seasons in light of
the new ozone standard level
of 0.075 ppm. Data collected
during additional months may
be necessary to alert the public
of all unhealthy days and
correctly identify nonattainment
areas. For example, 26 of
35 states that are not required
to monitor ozone in March do
so voluntarily, and in recent
years they have measured
ozone at unhealthy levels.
Similar unhealthy levels may
be happening in states not
monitoring ozone in March.
Required Ozone Monitoring Time Periods
Time Period
• Apr-Sep • Mar-Nov
Apr-Oct • May-Sep
Apr-Mov • May-Oct
Mar-Sep Jun-Sep
• Mar-Oct • Year round
Puerto Rico
NATIONAL AIR QUALITY STATUS AND TRENDS
1 5
-------
GROUND-LEVEL OZONE
WEATHER CONDITIONS INFLUENCE OZONE
In addition to emissions, weather also plays an
important role in the formation of ozone. A large
number of hot, dry days can lead to higher ozone levels
in any given year, even if ozone-forming emissions
do not increase. To better understand how ozone is
changing, EPA assesses both the changes in emissions
as well as weather conditions. EPA uses a statistical
model to calculate a weather adjustment factor that
estimates the influence of atypical weather on ozone
formation. The adjustment factor is derived from using
weather variables such as temperature and humidity.
This provides a clearer picture of the underlying
pollutant trend from year to year, making it easier to
see the effect of changes in emissions on air quality.
Geographic differences in the weather adjustment
factor for 2007 are shown in Figure 10. In 2007, weather
contributed to higher than expected ozone formation in
the East, as indicated by values greater than 0.005 ppm.
Weather Adjustments (ppm)
0.007
I
Higher ozone
than expected
J Lower ozone
-0.007 ^•than expected
Weather adjustments unavailable
Figure 10. Difference between 2007 observed and adjusted ozone concentrations (average daily maximum 8-hour ozone for May-
September). The map shows areas where weather contributed to higher or lower ozone concentrations than expected. Estimated
changes for locations farther from monitoring sites (dots on map) have the largest uncertainty.
Note: For information on the statistical model, read "The effects of meteorology on ozone in urban areas and their use in assessing ozone trends/
by Louise Camalier, William Cox, and Pat Dolwick of the U.S. EPA. Atmospheric Environment 41, Pages 7127-7137, 2007.
1 6
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
Figure 11 shows ozone trends for 2001 through
2007, averaged across selected sites before and after
adjusting for weather. At the national level, observed
ozone levels show a very small decrease of one percent
between 2001 and 2007 compared with a larger
decrease of eight percent after removing the influence
of weather. By examining the data separately for
California vs. eastern U.S., it is dear that the majority
of the ozone improvement, after adjusting for weather,
occurs in the East (on the order of 10 percent).
The largest change in observed and weather adjusted
ozone in the East occurred during the period from
2002 through 2004, and was especially noticeable
between 2003 and 2004. This relatively abrupt
change in ozone levels coincides with the large
oxides of nitrogen (NOx) emissions reductions
brought about from implementation of the NOx
SIP Call rule, which began in 2003 and 2004. This
significant improvement in ozone continues into
2007, i.e., weather-adjusted levels in 2007 are the
lowest over the 7-year period.
0.080-
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Q.
•£= 0.070 1
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| 0.060 f
o 0.055J
£ 0.050^
o :
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n ndn-:
National Trend 134 Sites
-- " "* •*• ^. _»_ ( __ __ _(
~~ -* " -
2001 to 2007: 1% decrease (observed)
2001 to 2007: 8% decrease (adjusted)
01
02
03
04
05
06
07
Monitoring Sites
- Rural (CASTNET)
» Urban (AQS)
£ 0.075^
Q. ;
•2= 0.070:
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1 0.060:
§ 0.055^
I 0.050-;
0 0.045 -i
n run -5
California Trend
^ -* •-- ^
' ~ — -»-'
2001 to
2001 to
2007: 5% decrease (observed)
2007: 0.5% increase (adjusted)
10 Sites
*.
01 02 03 04 05 06 07
— » — Observed trend
"E 0.075-=
Q.
— 0.070i
c
| 0.065-;
| 0.060^
o
§ °-055^
g 0.050:
0 0.045^
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Eastern
_^
— • —
2001 to
2001 to
U.S.
*s
s
s
2007
2007
Trend 80 Sites
.-*•-_ ^ " "'
* - - ^.^ '
0% decrease (observed)
10% decrease (adjusted)
01 02
Adjusted trend
03
04
05
06
07
Figure 11. Trends in average summertime daily maximum 8-hour ozone concentrations (May-September), before and after
adjusting for weather nationally, in California and in eastern states; and the location of urban and rural monitoring sites used
in the averages.
Notes: Urban areas are represented by multiple monitoring sites. Rural areas are represented by a single monitoring site. For more information
about the Air Quality System (AQS), visit http://www.epa.gov/ttn/airs/airsaqs. For more information about the Clean Air Status and Trends Network
(CASTNET), visit http://www.epa.gov/castnet/.
NATIONAL AIR QUALITY STATUS AND TRENDS
1 7
-------
GROUND-LEVEL OZONE
Air Quality Where You Live
EPA has several Web sites to help answer frequently asked questions regarding local air quality. To see air quality trends for
an individual area, visit the AirTrends Where You Live page at http://www.epa.gov/airtrends/where.html. Local trends are
available at individual monitoring locations for pollutants monitored there.
To get air quality information to compare different areas of the country, visit AirCompare at
http://www.epa.gov/aircompare. Select up to 10 counties across the country and nd out how many days in each county
the air was unhealthy last year for a speci c health concern (e.g., asthma). Also nd out which are the worst months. The
example below shows a comparison of seven counties near Atlanta, Ga.
Air
- Compare Air Quality of U.S. Cities
' '
Number of Unhealthy Days in Recent Years
i DeKalb, GA for Asthma or Other Lung Disease
30 -
2003 2004 2005 2006 2007
^ Unhealthy for Sensitive Groups
| Unhealthy
| Very Unhealthy
Also
available:
Historical
and monthly
profiles
Simple steps:
I. Select a health concern
2. Select a state (or states)
3. Select counties (red dots)
4. See the comparison
Number of Unhealthy Days in 2007
for Asthma or Other Lung Disease
10 20
i
Monthly Average Number of Unhealthy Days
in DeKalb, GA for Asthma or Other Lung Disease
60 •
5.0 •
4.0
:i o
2.0 •
1 0
0 0
A2 00 0,2.
Jan Feb Mar Apr May Jun Jul Aug. Sap Oct Nov Dec
I 1 Unhealthy lor Sensitive Groups
H Unhealthy
H Very Unhealthy
As of May 2008
1 8
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
PARTICLE
POLLUTION
Particle pollution refers to two
classes of particles based in part
on long-established information
on differences in sources,
properties, and atmospheric
behavior. EPA has set national
standards to protect against
the health and welfare effects
associated with exposures to fine
and coarse particles. Fine particles
are generally referred to as those
particles less than or equal to
2.5 micrometers (|am) in diameter,
PM2 5. PM10 (particles generally
less than or equal to 10 |jm in
diameter) is the indicator used for
the coarse particle standard.
2.5
TRENDS IN PM
CONCENTRATIONS
There are two national air
quality standards for PM2 5: an
annual standard (15 |ag/m3) and
a 24-hour standard (35 |jg/m3).
Nationally, annual and 24-hour
PM2 5 concentrations declined by
9 and 10 percent, respectively,
between 2001 and 2007, as shown
in Figure 12.
Annual
18:
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£ 8-
-------
PARTICLE POLLUTION
For each monitoring location, the maps in Figure 13
show whether annual and 24-hour PM2 5 increased,
decreased, or stayed about the same since the beginning
of the decade. When comparing two 3-year periods,
2001-2003 and 2005-2007, almost all of the sites show a
decline or little change in PM25 concentrations. Several
sites in California showed great improvement for both
the 24-hour and annual PM25 standards. One site in
Pennsylvania also showed great improvement in the
24-hour PM2 5 concentrations. Eighteen of the 618 sites
showed an increase in annual PM2 5 concentrations
greater than 1 Lig/m3. These sites were located in
Montana, Arizona, Texas, Arkansas, Louisiana, Alabama,
South Carolina, Illinois, and Wisconsin. Of the 18 sites
that showed an increase in annual PM2 5 concentrations,
only two (Birmingham and Houston) were above the
level of the annual PM2 5 standard for the most
recent year of data (2007). Fifty-eight sites showed
an increase in 24-hour PM2 5 concentrations greater
than 3 Lig/m3. Of the 58 sites that showed an
increase, 39 were below the level of the 24-hour
PM2 5 standard for the most recent year of data and
19 were above. The 19 sites above the standard were
located in or near the following metropolitan areas:
Birmingham, Ala.; Nogales, Ariz.; Chico, Calif.;
Paducah, Ky.; Cincinnati, Ohio; Kalamath Falls,
Ore.; Pittsburgh, Pa.; Clarksville, Tenn.; Provo, Utah;
Green Bay, Wis.; Madison, Wis.; and Milwaukee,
Wis. Due to the influence of local sources, it is
possible for sites in the same general area to show
opposite trends, as in the case of the Pittsburgh area
for the 24-hour standard.
Annual
Change in Concentration (pg/m3)
O Increase of 1.1 to 3 (18 Sites)
o Little Change +- 1 (450 Sites)
O Decrease of 1.1 to 3 (134 Sites)
® Decrease of more than 3 (16 Sites)
Puerto Rico
24-hour
Change in Concentration
O Increase of 3.1 to 11 (58 Sites)
o Little Change +- 3 (382 Sites)
O Decrease of 3.1 to 11 (164 Sites)
• Decrease of 11.1 to 15 (9 Sites)
£ Decrease of more than 15 (5 Sites)
Puerto Rico
Figure 13. Change in PM25 concentrations in }ig/m3, 2001-2003 vs. 2005-2007 (3-year average
of annual and 24-hour average concentrations).
20
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
In 2007, the highest annual average PM2 5
concentrations were in California, Arizona, Alabama,
and Pennsylvania, as shown in Figure 14. The highest
24-hour PM2 5 concentrations were in California, Idaho,
and Utah. Even though California and Pennsylvania
showed the greatest improvement since the start of the
decade, they had some of the highest concentrations in
2007.
Some sites had high 24-hour PM2 5.
but low annual PM_
. concentrations
^2 5 concentrations, and vice versa.
Sites that have high 24-hour concentrations but low
or moderate annual concentrations exhibit substantial
variability from season to season. For example, sites
in the Northwest generally have low concentrations
in warm months but are prone to much higher
concentrations in the winter. Factors that contribute to
the higher levels in the winter are extensive woodstove
use coupled with prevalent cold temperature
inversions that trap pollution near the ground.
Nationally, more sites exceeded the level of the 24-hour
PM2 5 standard than exceeded the level of the annual
PM2 5 standard, as indicated by yellow and red dots
on the maps below. About one-third of the sites that
exceeded either standard exceeded both standards.
Annual
Concentration Range (pg/m3)
• 3.4-12.0 (418 Sites)
O 12.1 -15.0 (366 Sites)
O 15.1 -18.0 (86 Sites)
• 18.1 -22.5 (14 Sites)
Puerto Rico
24-hour
Concentration Range (|jg/m3)
• 7- 15 (38 Sites)
O 16-35 (662 Sites)
O 36-55 (166 Sites)
• 56-73 (18 Sites)
Puerto Rico
Figure 14. Annual average and 24-hour (98th percentile 24-hour concentrations) PM2 5 concentrations in ug/m3, 2007.
NATIONAL AIR QUALITY STATUS AND TRENDS
2 1
-------
PARTICLE POLLUTION
WEATHER CONDITIONS INFLUENCE PM25
As for ozone, in addition to emissions, weather plays
an important role in the formation of PM2 5. Figure 15
shows trends in PM25 from 2001 through 2007, before
and after adjusting for weather. PM2 5 levels are
monitored throughout the year, separate graphs are
shown for the warm and cool months. After adjusting
for weather, PM2 5 concentrations have decreased by
approximately 11 percent in both the warm and the
cool season between 2001 and 2007. Weather influences
during the warm season are generally larger than
for the cool season, which is consistent with seasonal
changes in emissions and temperature effects on the
formation of secondary particle pollutants.
18
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£ 14
12-
10
Annual Trend
69 Sites
2001 to 2007: 10% decrease (observed)
2001 to 2007: 10% decrease (adjusted)
01
02
03
04
05
08
18
S-H
lu.
,2H
10
Cool Months Trend
Sites
2001 to 2007: 14% decrease (observed)
2001 to 2007: 11% decrease (adjusted)
01 02 03 04 05 06 07
— •• — Observed trend
07
18
Monitoring Sites
• Urban (AQS)
! 16-
i
1 14-
\ 12-
E
10
Warm Months Trend
69 Sites
2001 to 2007: 4% decrease (observed)
2001 to 2007: 11% decrease (adjusted)
01 02 03
Adjusted trend
04
05
06
07
Figure 15. Trends in annual, cool months (October-April), and warm months (May-September) average PM25 concentrations,
before and after adjusting for weather, and the location of urban monitoring sites used in the average.
TRENDS IN PM25 COMPOSITION 2002-2007
The mixture of different chemical components which
make up PM2 5 varies by season and location. This
is true because of the differences in emissions and
weather conditions that contribute to the formation
and transport of PM2 5. In general, PM2 5 is primarily
composed of sulfate, nitrate, organic carbon, and, to a
lesser degree, elemental carbon and crustal material.
Figure 16 shows regional trends in the composition of
PM25 from 2002 to 2007 for warm and cool months.
Sulfate levels are generally higher in the warm months
and can account for the largest chemical component of
PM2 5 mass. Sulfate concentrations are their lowest in
the Northwest. Also, the sulfate portion of PM2 5 mass is
lower in the Northwest than in any other region. Slight
declines in sulfate levels are shown in the Northeast
and Southeast during the cooler months. The highest
sulfate concentrations appeared in the Southeast,
Northeast, and Midwest during warm months of 2005,
partly due to atypical weather conditions. The largest
sources of sulfate in the eastern U.S. are SO2 emissions
from electric utilities and industrial boilers. In southern
California and port cities in the Northwest, sulfates
likely come from marine vessels.
Organic carbon is also a major component of PM2 5
throughout the year in all regions. Organic carbon
concentrations are highest in southern California and
the Southeast. Organic carbon levels are the largest
component of PM2 5 in southern California and the
Northwest during the cool months. Declines are shown
22
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
year-round for southern California and during the
warm months in the Northeast. The largest sources of
organic carbon are VOCs and direct carbon emissions
from highway vehicles, non-road mobile, waste
burning, wildfires, and vegetation. In the western U.S.,
fireplaces and woodstoves are important contributors
to organic carbon.
Nitrate concentrations are higher in the cool months
than in the warm months. The lowest nitrate levels
are in the Northeast and the Southeast. Nitrate levels
have declined substantially in southern California and
slightly in all the other regions, except the Northwest,
which shows no discernible trend. The largest sources
of nitrates are NOx emissions from highway vehicles,
non-road mobile, electric utilities, and industrial
boilers. Ammonia from sources such as fertilizer and
animal feed operations contributes to the formation of
sulfates and nitrates that exist in the air as ammonium
sulfate and ammonium nitrate.
The remaining two components, elemental carbon
and crustal material, are comparatively small but also
exhibit some seasonal variability.
Cool
Warm
20
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02 03 04 05 06 07 02 03 04 05 06 07
Southeast
02 03 04 05 06 07 02 03 04 05 06 07
Southern California
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02 03 04 05 06 07 02 03 04 05 06 07
02 03 04 05 06 07
02 03 04 05 06 07
I Sulfate I I Nitrate
I I Organic Carbon
Elemental Carbon
I Crustal
Northwest
North Central
Midwest
Figure 16. Regional and seasonal trends in annual
PM25 composition in }ig/m3, 2002-2007.
Southern* •
California Southwest
. . .
+ , . Northeast
' « ..*
Southeast
Note: This figure is based on 42 monitoring locations with the most complete data from the national chemical speciation network for 2002-2007.
There were no sites with complete data in the Southwest. For related information, read "Retained nitrate, hydrated sulfates, and carbonaceous
mass in federal reference method fine particulate matter for six eastern U.S. cities," by N. H. Frank, /. Air & Waste Manage. Assoc. 56, Pages 500-511,
2006.
NATIONAL AIR QUALITY STATUS AND TRENDS
23
-------
PARTICLE POLLUTION
TRENDS IN PM10 CONCENTRATIONS
Nationally, 24-hour PM10 concentrations
declined by 21 percent between 2001 and 2007
as shown in Figure 17.
When comparing two 3-year periods, 2001-
2003 and 2005-2007, most of the sites (nearly
90 percent) showed a decline or little change
in PM10 as shown in Figure 18. Twenty sites
located in the Southwest, South Carolina,
Missouri, and Wyoming showed a greater
than 50 |jg/m3 decline. Seventy-four sites
showed an increase of greater than 10 |jg/m3
over the trend period. Four of these sites
(Houston, Texas; Rock Springs, Wyo.; Albany,
Ga.; and Las Cruces, N.M.) showed large
increases of 50 |jg/m3 or more.
iuu -
„. 140-
m
1> 120~
~ 100-
•| 80-
1 60-
I 40-
° 20:
n .,
National Standard 734 sites
90 percent of sites are below this line.
Average J
1 ^^^^^^^^
10 percent of sites are below this line.
01 02 03 04 05 06
2001 to 2007: 21% decrease
07
Figure 17. National PMW air quality trend, 2001-2007 (second
maximum 24-hour concentration).
Change in Concentration {[jg/m3)
O Increase of 10.1 to 73 (74 Sites)
O Little Change+-10 (380 Sites)
O Decrease of 10.1 to 30 (123 Sites)
Q Decrease of 30.1 to 50 (19 Sites)
^B Decrease of more than 50 (20 Sites)
Alaska
Puerto Rico
Figure 18. Change in PMW concentrations inpg/m3, 2001-2003 vs. 2005-2007 (3-year average of
annual average concentrations).
24
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
Concentration Range (|jg/m
• 2 - 54 (424 Sites)
O 55-154 (424 Sites)
O 155-255 (20 Sites)
• 256-2736 (12 Sites)
Puerto Rico
Figure 19 shows that in 2007, the
highest PM10 concentrations were
located in California, Nevada,
Arizona, and New Mexico. This
is also where some of the sites
showed a greater than 50 |jg/m3
decline. Highest concentrations
are largely located in dry and/or
industrial areas with high coarse
particle sources.
Figure 19. PMW concentrations
in ug/m3, 2007 (second maximum
24-hour concentration).
Sustainable Skylines Initiative
EPA's Sustainable Skylines Initiative (SSI) is an innovative approach to achieve sustainable
air quality and other environmental improvements including reducing the six common air
pollutants, toxic air pollutants, and greenhouse gases. Participating cities may integrate
transportation, energy, land use, and air quality planning efforts to achieve measurable
emissions reductions within three years.
Sustahable Skyfaes
Each program is locally-driven, provides for collaboration
among multiple stakeholders, identi es and leverages resources
among public and private partners, and utilizes a consensus-
based approach. Initiatives to encourage use of sustainable
practices to help the air quality are already underway in Dallas,
Texas; Kansas City, Kan.; and Missouri. EPA plans to have 10 cities
in the program by the end of 2010.
Sustainable skyline projects include:
• Linking green building techniques with affordable housing
initiatives.
• Decreasing the amount of heated surfaces within the
central city.
• Increasing permeability of surfaces within the central city.
• Conducting pollution prevention audits for small businesses
to reduce energy consumption and environmental impacts.
• Reducing landscape equipment emissions through
sustainable lawn irrigation and turf management.
• Lowering vehicle emissions by increasing public
transportation and reducing vehicle miles traveled.
• Converting parking lots to parks.
• Reducing engine idling and applying retro ts to diesel
engines.
• Retro tting or replacing small off-road equipment to reduce
emissions.
For more information about Dallas, visit
http://www.sustainableskylines.org/Dallas/.
For more information about Kansas City, visit
http://www.epa.gov/region7/citizens/ssi.htm.
NATIONAL AIR QUALITY STATUS AND TRENDS
25
-------
LEAD
TRENDS IN LEAD CONCENTRATIONS
Nationally, concentrations of lead decreased
56 percent between 2001 and 2007, as shown in
Figure 20. The national average concentrations
shown are for 25 sites near large stationary
sources and 78 sites that are not near stationary
sources, 103 sites total. The typical average
concentration near a stationary source (e.g.,
metals processors, battery manufacturers, and
mining operations) is approximately 7 times the
typical concentration at a site that is not near a
stationary source. There are significant year-
to-year changes in lead concentrations at sites
near stationary sources; these reflect changes
in emissions due to changes in operating
schedules and plant closings. For example, lead
concentrations declined between 2001 and 2002
mostly due to lower lead concentrations at sites
in Herculaneum, Mo.
Figure 21 shows lead concentrations in 2007. Of
the 109 sites shown, 25 exceeded the new lead
standard (0.15 |jg/m3). These sites are located
in Alabama, Florida, Illinois, Indiana,
Minnesota, Missouri, Ohio, Pennsylvania,
Tennessee, and Texas. All of these sites are
located near stationary lead sources. New
requirements for monitoring near stationary
lead sources will be implemented in 2010.
Approximately 250 new locations will be
monitoring lead concentrations.
National Avg. (103 Sites)
Source Oriented Avg. (25 Sites)
Non-Source Oriented Avg. (78 Sites)
03 04 05 06
2001 to 2007: 56% decrease
Figure 20. National lead air quality trend, 2001-2007 (maximum
3-month average).
Note: 90 percent of sites are shown in the yellow area.
Concentration Range (jjg/m3)
• 0.00 - 0.07 (73 Sites)
O 0.08-0.15(11 Sites)
• 0.16-1.74 (25 Sites)
figure 21. Lead concentrations i
2007 (maximum 3-month averages).
Puerto Rico
EPA Strengthens the National Ambient Air Quality Standards for Lead
On October 15, 2008, EPA strengthened the National Ambient Air Quality Standards for lead. The level for the previous lead
standards was 1.5 M9/m3, not to be exceeded as an average for a calendar quarter, based on an indicator of lead in total
suspended particles (TSP). The new standards, also in terms of lead in TSP, have a level of 0.15 M9/m3, not to be exceeded as an
average for any three-month period within three years.
In conjunction with the revision of the lead standard, EPA also modified the lead air quality monitoring rules. Ambient lead
monitoring is now required near lead emissions sources emitting 1 or more tons per year, and also in urban areas with a
population equal to or greater than half a million people. Monitoring sites are required to sample every sixth day.
2 6
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
NO,, CO, AND SO
TRENDS IN NO2, CO, AND SO2
CONCENTRATIONS
Nationally, concentrations of nitrogen
dioxide (NO2) decreased 20 percent
between 2001 and 2007, as shown in
Figure 22. In 2007, NO2 concentrations
were the lowest of the seven year
period. All recorded concentrations
were well below the level of the annual
standard (0.053 ppm).
Figure 22. National NO2
air quality trend, 2001-2007
(annual average).
~ 0.05 -
Q.
& 0.04 -
o
'ro 0.03 -
•+—
§ 0.02 -
c
o
0 0.01 -
n -
31 3 sites
National Standard
90 percent of sites are below this line.
Average
10 percent of sites are below this line.
1
01
02
E
0.
a.
c
0
's
0)
o
0
0
IU -
8-
7-
6
5:
4 -
.
3-
•
2 -
1 -
n -
National Standard 322 sites
Average go percent of sites are below this line.
I
1
-
f
10 percent of sites are below this line.
01 02 03 04 05
2001 to 2007: 39% decrease
06
07
03 04 05 06
2001 to 2007: 20% decrease
07
Nationally, concentrations of 8-hour carbon
monoxide (CO) decreased 39 percent
between 2001 and 2007, as shown in
Figure 23. In 2007, CO concentrations
were the lowest in the past seven years.
All concentrations were below the 8-hour
standard (9 ppm). One site near Salt Lake
City, Utah, showed concentrations above the
level of the 1-hour standard (35 ppm).
Figure 23. National CO air quality trend,
2001-2007 (second maximum 8-hour average).
Nationally, concentrations of sulfur
dioxide (SO2) decreased 24 percent
between 2001 and 2007, as shown
in Figure 24. In 2007, annual SO2
concentrations were the lowest of the
seven year period. All concentrations
were below the level of the annual
standard (0.03 ppm). One site in Hawaii
showed concentrations above the level
of the 24-hour standard (0.14 ppm), due
to a nearby volcano.
Figure 24. National SO2 air quality
trend, 2001-2007 (annual average).
U.UJ3-
0.03-
E
g;0,025-
o 0.02-
nj
•g 0.015-
0>
2 0.01-
o
° 0.005-
? o
National Standard
90 percent of sit
Average
10 percent of sites are below this line.
I
406 sites
es are below this line.
I
1 02 03 04 05 06 0
2001 to 2007: 24% decrease
Downward trends in NO2, CO, and SO2 are the result of various national emissions control programs. Even though
concentrations of these pollutants are low with respect to national standards, EPA continues to track these gaseous
pollutants because of their contribution to other air pollutants (e.g., ozone and PM2 5) and reduced visibility. National
ambient air quality standards for these pollutants are under review.
NATIONAL AIR QUALITY STATUS AND TRENDS
2 7
-------
TOXIC AIR
POLLUTANTS
TRENDS IN TOXIC AIR POLLUTANT
CONCENTRATIONS
Under the Clean Air Act, EPA regulates 187 toxic air
pollutants. Toxitity levels, or the potential for adverse
effects on human health, vary from pollutant to
pollutant. For example, a few pounds of a relatively
toxic pollutant may have a greater health effect than
several tons of emissions of a less toxic pollutant. These
toxirity levels can vary by orders of magnitude between
pollutants. EPA has a recommended set of benchmark
toxitity levels for estimating the effects of exposure to
individual toxic air pollutants. For more information,
visit http://www.epa.gov/ttn/atw/toxsource/tablel .pdf.
Monitoring data are limited for most toxic air
pollutants. Because ambient monitoring data is so
limited for toxic air pollutants, EPA frequently relies
on ambient modeling studies to better define trends
in toxic air pollutants. One such modeling study,
the National-Scale Air Toxic Assessment (NATA),
is a nationwide study of ambient levels, inhalation
exposures, and health risks associated with emissions
of 177 toxic air pollutants (a subset of the Clean Air
Act's list of 187 toxic air pollutants). NATA examines
individual pollutant effects as well as cumulative
effects of many air pollutants on human health.
Figure 25 shows the estimated lifetime cancer risk
across the continental U.S. by county based on 2002
NATA model estimates. The national average cancer
risk level in 2002 is 36 in a million. Many urban areas
as well as transportation corridors show a risk above
the national average. From a national perspective,
benzene is the most significant toxic air pollutant for
which cancer risk could be estimated, contributing
over 30 percent of the average individual cancer
risk identified in the 2002 assessment. Though not
included in the figure, exposure to diesel exhaust is
also widespread. EPA has not adopted specific risk
estimates for diesel exhaust but has concluded that
diesel exhaust is a likely human carcinogen and ranks
with the other substances that the national-scale
assessment suggests pose the greatest relative risk to
human health.
Figure 26 shows the trends in ambient monitoring
levels for some of the important toxic air pollutants
Median Risk Level
0 - 25 in a Million
26 - 50 in a Million
51 - 75 in a Million
•176 -100 in a Million
^•> 100 in a Million
Puerto Rico
Alaska
Figure 25. Estimated county-level cancer risk from the 2002 National Air Toxics Assessment (NATA2002).
Darker colors show greater cancer risk associated with toxic air pollutants.
28
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
identified by NATA. When the median
percent change per year (marked by an x
for each pollutant shown) is below zero, the
majority of the sites in the U.S. are showing
a decrease in concentrations. Ambient
monitoring data show that for some of the
toxic air pollutants of greatest widespread
concern to public health (shown in yellow),
1,3-butadiene, benzene, tetrachloroethylene,
and 1,4-dichlorobenzene concentration levels
are declining at most sites. Concentrations
of VOCs such as 1,3-butadiene, benzene,
styrene, xylenes, and toluene decreased
by approximately 5 percent or more per
year at more than half of all monitoring
sites. Concentrations of carbonyls such
as formaldehyde, acetaldehyde, and
propionaldehyde were equally likely to have
increased or decreased. Chlorinated VOCs
such as tetrachloroethylene, dichloromethane,
and methyl chloroform decreased at more
than half of all monitoring sites, but decreases
among these species were much less
consistent from site to site than among the
other VOCs shown. Lead particles decreased
in concentration at most monitoring sites;
trends in other metals are less reliable due
to the small number of sampling sites available for
analysis.
In 2003, in an effort to improve accuracy and
geographic coverage of monitoring, EPA, working with
its state and local partners, launched the National Air
Toxics Trends Station (NATTS) program, a national
monitoring network for toxic air pollutants. The
principal objective of the NATTS network is to provide
long-term monitoring data across representative
areas of the country for NATA priority pollutants
(e.g., benzene, formaldehyde, 1,3-butadiene, acrolein,
and hexavalent chromium) in order to establish
overall trends. The initial 23 stations were established
between 2003 and 2005, two stations were added in
2007 and two more in 2008 for a total of 27 NATTS
sites. In addition, the list of pollutants monitored was
expanded to include poly cyclic aromatic hydrocarbons
(PAHs), of which naphthalene is the most prevalent.
Figure 26. Distribution of changes in
ambient concentrations at U.S. toxic
air pollutant monitoring sites, 2000-
2005 (percent change in annual average
concentrations).
(Source: McCarthy M.C., HafnerH.R.,
Chinkin L.R., and CharrierJ.G. [2007]
Temporal variability of selected air toxics
in the United States. Atmos. Environ. 42
[34], 7180-7194)
Notes: 10th and 90th percentiles are excluded
if fewer than 10 monitoring sites were available
for analyses. For chloroform and nickel, the 90th
percentile percent changes per year are cut off
at 30.
1,4-Dichlorobenzene
Carbon Tetrachloride
Chloroform
Chloromethane
Dichloromethane
Methyl Chloroform
Tetrach loroethylene
Trich loroethylene
1,3-Butadiene
2,2,4-Trimethylpentane
Benzene
Ethyibenzene
Isopropylbenzene
M-P-Xylenes
N-Hexane
O-Xylene
Styrene
Toluene
Acetaldehyde
Formaldehyde
Propionaldehyde
Lead (Tsp)
Manganese (Tsp)
Nickel (Tsp]
VOCs
Carbonyls
*I
Metals
-30 -20 -10 0 10 20 30
Percentage Change per Year
Median Percentage
Change/Year
10th X 90th
Percentile Percentile
NATIONAL AIR QUALITY STATUS AND TRENDS
2 9
-------
TOXIC AIR POLLUTANTS
In addition to the NATTS program, about 300
monitoring sites are currently collecting data to help
air pollution control agencies track toxic air pollutant
levels in various locations around the country. State,
local, and tribal air quality agencies operate these sites
to address specific concerns such as areas of elevated
concentrations or "hot spots," environmental justice
concerns, and/or public complaints.
Figure 27 shows the locations of the toxic air pollutant
monitoring sites. A majority of these sites are located
in or near densely populated areas. Most sampling
is conducted on a l-in-6-day schedule for a 24-hour
period. For more information about ambient air quality
monitoring programs, visit http://www.epa.gov/ttn/
amtic/.
Monitoring Network
* NATTS
• UATMP
A Other
Puerto Rico
Figure 27, Toxic air pollutant monitoring sites operating in 2007 (by monitoring program).
Note: Some agencies use EPA-contracted sampling and laboratory analysis support services at the sites that are not NATTS program sites; these
sites collectively are referred to as the Urban Air Toxics Monitoring Program (UATMP). At other monitoring sites, agencies perform their own
laboratory analyses or use non-EPA contracted laboratories.
30
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
Local Short-term Toxic Air Pollutant Monitoring Projects
Due to the local nature of toxic air pollutant problems in 2004, EPA began funding local-scale monitoring projects. Typically
these projects collect one to two years of monitoring data. To date, EPA has funded 51 projects and 25 have been completed.
The goal of local monitoring is to provide more
flexibility to address middle- and neighborhood-
scale (0.5 km to 4 km) issues that are not
handled well by national networks. Objectives
for these projects include:
• characterizing the degree and extent of
local toxic air pollutant problems
• identifying and profiling local toxic air
pollutant sources
• developing and assessing emerging
measurement methods
• verifying the success of toxic air pollutant
reduction activities
Results from these efforts are used to identify
emission reduction options to be implemented
Woodson site for the Hopewell Urban Air Toxics special study currently Qj ^e \oca\ |eve|
in progress located at Carter G. Woodson Middle School in Hopewell, Va.
Apartment complexes can be seen in the background.
Detroit Exposure and Aerosol Research Study (DEARS)
A research study that the U.S. Environmental Protection Agency conducted
in Detroit, Michigan, named the Detroit Exposure and Aerosol Research Study
(DEARS), will help develop data that improves our understanding of human
exposure to various air pollutants in our environment. The primary objective of
DEARS was to compare air pollutant concentrations measured at central or
community air monitoring stations with those measured in various neighborhoods in
the Detroit, Michigan, area.
The study collected air quality samples over a three-year period (2004 through
2007) involving roughly 120 adults, randomly selected from among seven
neighborhoods. These neighborhoods were selected because they represent a
variation of potential industrial and regional source influences, housing type/age,
and proximity to mobile emissions sources. Sampling included personal, indoor,
backyard, and community monitors. Data were collected on particle pollution and
toxic air pollutants.
These are the key questions to be addressed:
• How do air pollutant concentrations measured at community sites relate to
those from residential indoor, outdoor, and personal monitoring?
• Can air pollutant concentrations monitored at community sites adequately
represent estimates of what local residents are exposed to and the sources of
these pollutants?
Participants engaged in five days of summertime monitoring and five days of
wintertime monitoring per year. The summer and winter data collections provide
important information on seasonal influences on pollutant concentrations and
personal exposures to various sources.
Early findings indicate pollutant exposures may vary greatly among individuals
living in the same area. The indoor air environment often highly influences individual
exposures to some pollutant species, including those associated with volatile
organic compounds and particle pollution. The movement of air into and out of the
home was determined to be highly seasonal (nearly twice as high in the summer).
This resulted in much higher exposures of individuals to particle pollution formed
outside during the summer as compared to the winter. And, while the outdoor
environment was a significant contributor of pollutants to local air quality outside
homes close to major roadways, the impact of mobile-source related pollutants
on air quality as a function of distance to the roadway was clearly evident. The
impact of mobile-source related pollutants on air quality fell to near-background
levels as distances from the roadway approached 300 meters.
(Source: http://www.epa.gov/dears/, photos courtesy of EPA)
NATIONAL AIR QUALITY STATUS AND TRENDS
3 1
-------
ATMOSPHERIC
DEPOSITION
TRENDS IN ATMOSPHERIC DEPOSITION
Pollution in the form of acids and acid-forming
compounds (such as sulfur dioxide [SO2] and oxides
of nitrogen [NOJ) can deposit from the atmosphere to
the Earth's surface. Between the 1989-1991 and 2005-
2007 time periods, sulfate deposition decreased over
30 percent in the Northeast and the Midwest, as shown
in Figure 28. In addition, nitrate deposition decreased
by about 30 percent in the Mid-Atlantic and Northeast,
and 20 percent in the Midwest. These reductions have
led to improving water quality in lakes and streams.
Most of these improvements are due to reductions
in SO2 and NOx emissions from electric utilities and
industrial boilers. The Acid Rain Program and the NOx
SIP Call in the East have led to significant reductions in
SO, and NO emissions.
• SO2 emissions have been reduced by more
than 6.7 million tons from 1990 levels, or about
43 percent. Compared to 1980 levels, SO2 emissions
from power plants have dropped by more than
8 million tons, or about 48 percent. In 2007, annual
SO2 emissions fell by over 400,000 tons from 2006
levels.
• NOx emissions have been reduced by about
3 million tons from 1990 levels, so that emissions
in 2007 were less than half the level anticipated
without the Acid Rain and NOx SIP Call programs.
Ongoing review of the NO2 and SO2 secondary
standards, which is scheduled to be completed in 2010,
is addressing residual atmospheric deposition.
1989-1991
2005-2007
• Wet SO*2'
1989-1991
2005-2007
Figure 28. Three-year average deposition of sulfate (wet SO^~) and nitrate (wet NO}~) in 1989-1991 and 2005-2007. Dots show
monitoring locations. (Data source: National Atmospheric Deposition Program, http://nadp.sws.uiuc.edu/)
32
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
Mercury in the Environment
Mercury does not naturally occur as pure "quicksilver" but usually occurs as its principal ore cinnabar
(HgS), one of 25 mercury-containing minerals that make up about 0.5 parts per million of the Earth's
crust. Mercury is used in industry, commerce, mining, metallurgy, manufacturing, medicine, and
dentistry. Human sources of atmospheric mercury include by-products of coal combustion, municipal
and medical waste incineration, mining of metals for industry, and many others. Natural sources of
atmospheric mercury include out-gassing from volcanoes and geothermal vents, and evaporation
from naturally enriched soils, wetlands, and oceans. Atmospheric mercury concentrations can vary
greatly depending on the location. Away from sources, elemental mercury concentrations are
normally about 1.4 to 1.6 ng/m3 and reactive gaseous and particle-bound mercury concentrations
are normally below 0.05 ng/m3. Close to sources, and in unique environments, concentrations can
range widely, from 0.1 to over 100 ng/L in some outliers. Wet deposition could be responsible for
50-90 percent of mercury loading to many inland water bodies.
Mercury in the air is usually of little direct concern. But when mercury is washed from the air by
precipitation into our streams and lakes, it is transformed into highly toxic methyl-mercury that can
build up in fish. People are then exposed to mercury by eating fish.
Tracking progress and results is a critical
step in understanding mercury in the
environment. Since 1996, the Mercury
Deposition Network (MDN) provides
measurements of the amount of mercury
in rain; the network now has more than 100
sites. In 2006 the highest concentrations
of mercury wet-deposition are shown in
the eastern U.S. Between 1996 and 2005,
significant decreases in mercury wet-
deposition concentrations were found
at about half of 49 selected sites. Several
sites in the mid-Atlantic and northeast
show decreases greater than 1.5 percent.
Technologies used to remove NOx, SOx
, and particles also reduce mercury
emissions ("Control of Mercury Emissions
from Coal-fired Electric Utility Boilers: Interim
Report", EPA-600/R-01-109, April 2002).
For more information about the MDN, visit
http://nadp.sws.uiuc.edu/mdn/.
National Almosphenc Deposition Program/Mercury Deposition Network
NATIONAL AIR QUALITY STATUS AND TRENDS
33
-------
VISIBILITY IN
SCENIC AREAS
TRENDS IN VISIBILITY
EPA monitors visibility trends
in 155 of the 156 National parks
and wilderness areas meeting the
criteria established in the 1977 Clean
Air Act amendments. Long-term
trends in visibility on the annual
20 percent best and worst visibility
days are shown in Figure 29. Most
locations show improving visibility
(decreasing haze) for the best
visibility days, only Everglades
National Park in Florida shows
increasing haze. Five locations —
Mt. Rainier National Park, Wash.;
Great Smoky Mountains National
Park, Tenn.; Great Gulf Wilderness,
N.H.; Canyonlands National
Park, Utah.; and Snoqualmie Pass,
Wash.—show a notable decrease in
haze for the worst days.
The Regional Haze Rule requires
states to identify the most effective
means of preserving conditions
in these areas when visibility
is at its best—based on the best
20 percent visibility days—and
to gradually improve visibility
when it is most impaired—based
on the worst 20 percent visibility
days. States are required to adopt
progress goals for improving
visibility, or visual range, from
baseline conditions (represented
by 2000 to 2004) to achieve natural
background conditions within
60 years (represented by 2064).
States determine whether they are
meeting their goals by comparing
visibility conditions from one five-
year average to another (e.g., 2000-
2004 to 2013-2017). The glide path
to natural conditions in 2064 for the
Shenandoah National Park is shown
in Figure 30.
20% Worst Days
Trends in Visibility
^ Increasing Haze
Possible Increasing Haze
No trend
Possible Decreasing Haze
Decreasing Haze
20% Best Days
Figure 29. Trends in visibility on the 20 percent worst and best visibility
days, 1996-2006.
(Source: http://www.nature.nps.gov/air/)
Note: Visibility trends using a haze index for the annual average for the 20 percent best and worst visibility days are based on aerosol
measurements collected at Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring sites. The haze index is measured
in deciviews (dv), a visibility metric based on the light extinction coefficient that expresses incremental changes in perceived visibility. Sites
having at least six years of complete data were used to compute the change in dv per year over the trend period and its statistical significance.
34
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
35
30
H- 25
co 20
Glide path
— — 5-year rolling average
2018 Target
25. 1 dv
2064 Natural Background
11.4 dv
) G> O) (?) O O O i
) C> C> CT) en O O p i
- CM CN1 CN i
I ^ (£> CO O
(D CO
OOO
I (M i
Figure 30. Glide path to natural conditions in 2064 for Shenandoah (deciviews).
(Source: Visibility Improvement State and Tribal Association of the Southeast—VISTAS)
Notes: A change of one deciview is a change in visibility that is descernable. The figure shows a
5-year rolling average for the 20 percent worst visibility days.
Visibility at Great Smoky Mountains National Park
Visibility at Great Smoky Mountains National Park for the 20 percent haziest days in the baseline period 2000-2004
(30.3 deciviews) was among the poorest in the country. However, projected improvements in visibility in the Southern
Appalachian Mountains, such as the Great Smoky Mountains, are among the largest in the country. Ammonium sulfate is the
major contributor to haze in the southeastern U.S. There has been a small but significant reduction in sulfate and corresponding
improvement in visibility at Great Smoky Mountains National Park between 1990 and 2004. These improvements are due
primarily to SO2 emissions reductions under the Acid Rain Title IV provisions of the 1990 Clean Air Act Amendments.
| Visual Range (km)
| Ammonium Sulfate (ng/
2000-2004 2018 Model
30.3 deciviews Projection
23.5 deciviews
Natural Visibility
Conditions
11.1 deciviews
Visibility Improvement State and Tribal Association of the Southeast (VISTAS) modeling projects that emissions reductions under
existing state and federal regulations will significantly improve visibility by 2018. The uniform rate of progress for improving visibility
between baseline conditions and natural background would mean visibility of 25.8 deciviews in 2018; modeling indicates that
visibility in 2018 will be 23.5 deciviews, better than the uniform rate of progress, and is a 6.8 deciview improvement compared to
baseline conditions (2000-2004). Natural visibility conditions on the 20 percent haziest days at Great Smoky Mountains National
Park are projected to be 11.1 deciviews. Considerable additional progress is needed to achieve natural visibility.
(Source: Images from WinHaze Visual Air Quality Model, Air Resource Specialists, Inc. and Jim Renfro, Great Smoky
Mountains National Park)
NATIONAL AIR QUALITY STATUS AND TRENDS
35
-------
CLIMATE CHANGE
AND AIR QUALITY
CLIMATE AND AIR QUALITY
Climate and air pollution are closely coupled.
Ground-level ozone absorbs solar radiation, and thus
contributes to increases in global temperature. Particle
pollution scatters or absorbs solar radiation and
changes cloud formation processes and the amount
of cloud cover. The net effect of particle pollution is
cooling as scattering generally dominates.
Changes in climate affect air quality. Warming of the
atmosphere increases the formation of ground-level
ozone, while the overall directional impact of climate
change on particle pollution in the U.S. remains
uncertain.
Because of these links between climate and air quality,
the National Academy of Sciences recommends that
air pollution and climate change policies be developed
through an integrated approach. A number of strategies
being discussed for climate—energy efficiency,
renewable energy, and reducing the number of vehicles
on the highway will provide reductions in emissions
that contribute to multiple air quality concerns such
as ozone and particle pollution, toxic air pollutants,
atmospheric deposition, and visibility.
TRENDS IN GREENHOUSE GAS EMISSIONS
AND CLIMATE
EPA, in collaboration with other government
agencies, tracks both changes in climate and changes
in greenhouse gas emissions. Figure 31 shows the
trends in domestic greenhouse gas emissions over
time in the U.S. The dominant gas emitted is carbon
dioxide (mostly from fossil fuel combustion). Total
U.S. greenhouse gas emissions increased 15 percent
between 1990 and 2006.
A number of EPA scientists participate on the
Intergovernmental Panel on Climate Change (IPCC),
an international scientific body that provides
information about the causes of climate change and
its potential effects on the environment. In a series of
comprehensive reports completed in 2007, the IPCC
concludes that "warming of the climate system is
unequivocal, as is now evident from observations of
increases in global average air and ocean temperatures,
widespread melting of snow and ice, and rising global
average sea level." Average global temperatures have
been rising and the warming is accelerating.
MFCs, PFCs, & SF61
Nitrous Oxide
Methane
Carbon Dioxide
8000
6000
S
O'
o
p
4000
2000
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06
Figure 31. Domestic greenhouse gas
emissions in teragrams of carbon dioxide
equivalents (Tg CO2 ea), 1990-2006.
(Source: http://epa.gov/climatecha.nge/
emissions/usinventoryreport.html)
Notes: A teragram is equal to 1 million
metric tons. Emissions in the figure include
fluorocarbons (HFCs, PFCs) and sulfur
hexafluoride (SF6).
36
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
CHANGES IN CLIMATE AFFECT AIR QUALITY
Due to the warming, the IPCC projects with
virtual certainty "declining air quality in cities."
In summarizing the impact of climate change on
ozone and particle pollution, the IPCC concludes
that "future climate change may cause significant air
quality degradation by changing the dispersion rate
of pollutants, the chemical environment for ozone
and particle pollution generation, and the strength of
emissions from the biosphere, fires, and dust." Large
uncertainties remain, limiting our ability to provide
a quantitative description of the interactions between
air quality and climate change. However, as noted in
the following two examples, research is under way
that will provide an improved understanding of these
connections.
Using estimates from a computer model that assumes
continued growth in global GHG emissions, a study
cited in the 2007 IPCC report shows how ground-level
ozone in the New York metropolitan area may increase
from current levels given future climate change.
Figure 32 shows this study projects daily 1-hour ozone
increases of 0.0003 to 0.0043 ppm across the region due
to climate change alone in the 2050s compared to the
1990s.
Pollutants from forest fires can affect air quality for
thousands of miles. The IPCC reported that in North
America wildfires are increasing and in a warmer
future are likely to intensify with drier soils and longer
growing seasons. Figure 33 shows increases in the
annual frequency of large (>100,000 hectares) western
U.S. forest wildfires (bars) associated with the mean
March through August temperature. In the last three
decades, the wildfire season in the western U.S. has
increased by 78 days in response to a spring-summer
warming of 0.87°C.
Change in Ozone (ppm)
EH 0.0003 - 0.001
0,0011 -0.002
0.0021 -0.003
0.0031 -0.004
0.0041 - 0.0043
Figure 32. Estimated changes in 1-hour daily maximum
ozone concentrations (ppm) in the 2050s compared with
those in the 1990s for the New York metropolitan area,
under scenario Ml in which climate change alone drives
changes in air auality.
(Source: KnowIton K., et al. [2004] Assessing ozone-
related health impacts under a changing climate.
Environ. Health. Perspect., 112:1557-1563)
o;
03
;B
i
-CD
1970
1975
1980
1985
1990
1995
2000
Figure 33. Frequency of Western U.S. forest wildfires compared to spring-summer
temperature.
(Source: Westerling A.L., et al. [2006] Warming and earlier spring increase western
U.S. forest wildfire activity. Science, 313: 940-943)
NATIONAL AIR QUALITY STATUS AND TRENDS
37
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INTERNATIONAL TRANSPORT
OF AIR POLLUTION
While domestic sources of emissions are the primary
cause of most air pollution in our country, the U.S. is
both a source of pollution and a receiver of pollution
from other countries. Air pollution flows across
boundaries—not only between the U.S. and our closest
neighbors, Canada and Mexico, but also between
North America, Europe, and Asia, and to some extent,
between North America, Africa, and Central and
South America. International flow of air pollutants
into the U.S. contributes to observed concentrations
of ozone and particle pollution and deposition of
mercury, persistent organic pollutants (POPs), and acid
deposition.
TRANSPORT OF AIR POLLUTION
AFFECTS THE U.S.
The impact that international transport of air pollution
has on our ability to attain air quality standards or
other environmental objectives in the U.S. has yet to
be characterized (except in areas that are downwind
Summer
tat
INTERNATIONAL
TRANSPORT OF AIR
POLLUTION
of cities or sources in Mexico or Canada). Figure 34
illustrates major intercontinental transport pathways.
Estimates based on the available evidence are highly
uncertain, but suggest that the current contributions
of international transport to observed concentrations,
acid deposition and deposition of mercury are small.
Increased emissions of particle pollution, mercury, and
ozone precursors in developing countries associated
with economic growth may increase background levels
of these pollutants in the U.S.
For ozone and particle pollution, increased background
levels of these pollutants could potentially make it
more difficult for local and regional areas to achieve
the National Ambient Air Quality Standards and long-
term visibility improvement goals. Transported ozone
and particle pollution also contribute to radiative
forcing and global and regional climate change. For
mercury and POPs, international flows contribute
to deposition, and eventual human and ecosystem
chemical exposures. In some locations, especially in
Alaska, international sources are the dominant source
of contamination for these toxic air pollutants.
Winter
HOW 1SOW 120H SOW SOW JOW OE JOE 60E 90E I20E 150E ISOC
Figure 34. Major intercontinental transport pathways of CO emissions in the Northern Hemisphere. The colored boxes indicate
the four source and receptor regions used in the Task force on Hemispheric Transport of Air Pollution's (HTAP) on-going model
intercomp orison study. The arrows approximate the magnitude of main transport pathways in summer (June, July, August) and
winter (December, January, February), based on modelled average CO transport over 8-10 day periods. Light arrows indicate
transport generally near ground level (less than 3 km above the surface) and dark arrows indicate transport higher in the
atmosphere (more than 3 km above the surface).
(Source: Figure E-l, HTAP 2007. Adapted from Figure 2 ofStohl and Eckhardt [2004], with kind permission of Springer Science
and Business Media)
38
NATIONAL AIR QUALITY STATUS AND TRENDS
-------
International Efforts to
Address Air Pollution Transport
EPA is involved in a number of international efforts to
address air pollution transport, including:
• Reducing transborder air pollution transport, visit http://
www.epa.gov/airmarkets/progsregs/usca/index.htm
• Understanding intercontinental transport in the
northern hemisphere, visit http://www.htap.org
• Addressing global scale transport, visit http://chm.
pops.int and http://www.chem.unep.ch/mercury/
new_partnership.htm
• Building cooperative relationships to improve air
quality and reduce long-range transport of air
pollution in key countries, visit http://www.epa.gov/
oia/regions/
EFFORTS TO BETTER UNDERSTAND
TRANSPORT OF AIR POLLUTION
EPA and other agencies are working via treaties
and international cooperative efforts to address the
international transport of air pollution. Since 2001,
EPA has led collaborative efforts among many of the
leading U.S. researchers in the global atmospheric
chemistry community to improve our understanding
of trans-Pacific and trans-Atlantic transport. EPA and
the European Commission co-chair the Task Force on
Hemispheric Transport of Air Pollution, a multinational
Shipping and Aviation
>ns
Shipping and aviation are two of the fastest growing
sources of emissions globally, with important
consequences for air quality. Emissions from both sectors
have received increased attention and the International
Maritime Organization recently acted to strengthen
emission controls on ocean-going ships.
effort to better understand the soures, transport, and
impacts of air pollution in the northern hemisphere.
In 2008, EPA, with contributions from NOAA, NASA,
and the National Science Foundation (NSF), has
sponsored a National Academy of Sciences study to
examine the significance of the international transport
of air pollutants for air quality, atmospheric deposition,
and climate change.
Tracking Pollutant
Transport with Satellites
During the 2004 summer, the largest Alaskan
wild fire event on record occurred in late
June-July and consumed 2.72 million hectares
of boreal forest. The figure shows aerosol
optical depth (AOD) data from the Moderate
Resolution Imaging Spectroradiometer (MODIS)
instrument aboard the Terra satellite for a
series of days in July 2004. The MODIS AOD is
plotted over the MODIS Terra true color image
for each day. This series of days shows high
aerosol concentrations (in red) associated with
long-range transport of the Alaskan wild fire
plume as it crosses over the northern border of
the U.S. on July 16. This aerosol plume travelled
south-eastward behind the cold front (evident
in the clouds captured in the MODIS true color
image) over the following days, eventually
affecting surface PM25 levels along the Eastern
U.S.
Aerosol optical depth (AOD) measurements
for a series of days in July 2004.
(Image provided by f. Szykman, EPA, and
C. Kittaka, SSAI-NASA/LaRC)
NATIONAL AIR QUALITY STATUS AND TRENDS
39
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TERMINOLOGY
TERMINOLOGY
AQI
AQS
ADD
CAA
CASTNET
CCSP
CO
dv
EC
EPA
FRM
GHG
MFCs
HTAP
IMPROVE
MODIS
NAAQS
NASA
NATTS
NET
NH3
NO
NOx
NO2
NSF
03
Pb
PFCs
PM
PM2.5
PM10
POP
ppm
SF6
SIP
sox
SO2
UATMP
voc
Air Quality Index
Air Quality System
aerosol optical depth
Clean Air Act
Clean Air Status and Trends Network
U.S. Climate Change Science Program
carbon monoxide
detiviews
elemental carbon
U.S. Environmental Protection Agency
Federal Reference Method
greenhouse gas
hydrofluorocarbons
Hemispheric Transport of Air Pollution
Interagency Monitoring of Protected Visual Environments
Moderate Resolution Imaging Spectroradiometer
National Ambient Air Quality Standards
National Aeronautics and Space Administration
National Air Toxics Trends Stations
National Emissions Inventory
ammonia
nitric oxide
oxides of nitrogen
nitrogen dioxide
National Science Foundation
ground-level ozone
lead
perfluorinated compounds
particulate matter
particulate matter (fine) 2.5 |jm or less in size
particulate matter 10 |jm or less in size
persistent organic pollutants
parts per million
sulfur hexafluoride
state implementation plan
sulfur oxides
sulfur dioxide
Urban Air Toxics Monitoring Program
micrometers
micrograms per cubic meter
volatile organic compound
40
NATIONAL AIR QUALITY STATUS AND TRENDS
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WEB SITES
Atmospheric Deposition
Acid Rain Program: http://www.epa.gov/airmarkets/progsregs/arp/index.html
Acid Rain Program 2006 Progress Report: http://www.epa.gov/airmarket/progress/arp06.html
National Atmospheric Deposition Program: http://nadp.sws.uiuc.edu/
Background/General Information
Air Quality Index: http://www.airnow.gov
Air Quality System: http://www.epa.gov/ttn/airs/airsaqs/
EPA's Clean Air Research Program: http://www.epa.gov/ord/npd/cleanair-research-intro.htm
EPA-Funded Particulate Matter Research Centers:
http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/outlinks.centers#19
Framework for Assessing the Public Health Impacts of Risk Management Decisions:
http://www.epa.gov/ORD/npd/hhrp/files/hhrp-framework.pdf
Health and Ecological Effects: http://www.epa.gov/air/urbanair/
Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air): http://depts.washington.edu/mesaair/
National Ambient Air Quality Standards: http://www.epa.gov/air/criteria.html
National Center for Environmental Assessment: http://cfpub.epa.gov/ncea/
National Particle Components Toxitity (NPACT) Initiative: http://www.healtheffects.org/Pubs/NPACT.pdf
Office of Air and Radiation: http://www.epa.gov/air/
Office of Air Quality Planning and Standards: http://www.epa.gov/air/oaqps/
Office of Atmospheric Programs: http://www.epa.gov/air/oap.html
Office of Transportation and Air Quality: http://www.epa.gov/otaq/
Climate Change
Climate change: http://www.epa.gov/climatechange/
U.S. Climate Change Science Program: http://www.climatescience.gov
Emissions and trends in greenhouse gases:
http://www.epa.gov/climatechange/emissions/usinventoryreport.html
Green Car Congress: http://www.greencarcongress.com/2008/06/us-vehicle-mile.html
Intergovernmental Panel on Climate Change: http://www.ipcc.ch
Traffic Volume Trends: http://www.fhwa.dot.gov/ohim/tvtw/tvtpage.cfm
Emissions and Control Programs
Emissions: http://www.epa.gov/air/emissions/
NOx Budget Trading Program/NOx SIP Call: http://www.epa.gov/airmarkets/progsregs/nox/sip.html
Toxic Air Pollutants
1999 National-Scale Air Toxics Assessment: http://www.epa.gov/ttn/atw/natal999/
Measurements and Trends
Air Quality Trends: http://www.epa.gov/airtrends/
Air Trends Design Values: http://www.epa.gov/air/airtrends/values.html
Clean Air Status and Trends Network (CASTNET): http://www.epa.gov/castnet/
EPA Monitoring Network: http://www.epa.gov/ttn/amtic/
Local air quality trends: http://www.epa.gov/airtrends/where.html
National Air Monitoring Strategy Information: http://www.epa.gov/ttn/amtic/monstratdoc.html
NATIONAL AIR QUALITY STATUS AND TRENDS 41
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National Core Monitoring Network: http://www.epa.gov/ttn/amtic/ncore/index.html
Trends in ozone adjusted for weather conditions: http://www.epa.gov/airtrends/weather.html
Visibility
National Park Service: http://www.nature.nps.gov/air/
Regional Haze Program: http://www.epa.gov/visibility
Visibility Information Exchange Web System (VIEWS): http://vista.cira.colostate.edu/views/
International Transport
International Maritime Organization: http://www.imo.org
FAA's Aviation Climate Change Research Initiative (ACCRI):
http://www.faa.gov/about/office_org/headquarters_offices/aep/aviation_climate/
Task Force on Hemispheric Transport of Air Pollution: http://www.htap.org
42
NATIONAL AIR QUALITY STATUS AND TRENDS
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