SEPA
United States
Environmental
Protection Agency
« '
Our Nation's Air
STATUS AND TRENDS THROUGH 2010
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Our Nation's Air
STATUS AND TRENDS THROUGH 2010
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina
EPA-454/R-12-001
February 2012
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Highlights
Air Pollution
Six Common Pollutants
Ozone
Particle Pollution
Lead
NO2, CO, and SO2
Toxic Air Pollutants
Climate Change and Air Quality
Appendix
More information and discussion on additional air quality topics are available at
http://www.epa.gov/airtrends/2010.
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Improving public health by reducing air pollution and
improving air quality is one of the U. S. Environmental
Protection Agency's (EPA's) top priorities. This
summary report presents EPA's most recent evaluation
of our nation's air quality status and trends through
2010.
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 has improved
significantly for the six common air pollutants.
These six pollutants are ground-level ozone, particle
pollution [particles 2.5 micrometers in diameter
and smaller (PM25) and particles 10 micrometers
and smaller (PM1(|)], lead, nitrogen dioxide (NO2),
carbon monoxide (CO), and sulfur dioxide (SO2).
Nationally, air pollution was lower in 2010 than in
1990 for:
8-hour ozone, by 17 percent
- 24-hour PM1Q, by 38 percent
- 3-month average lead, by 83 percent
- annual N O2, by 45 percent
- 8-hour CO, by 73 percent
annual SO2, by 75 percent
Nationally, annual PM2 5 concentrations were 24
percent lower in 2010 compared to 2001. 24-hour
PM2 5 concentrations were 28 percent lower in
2010 compared to 2001.
Ozone levels did not improve in much of the East
until 2002, after which there was a significant
decline. 8-hour ozone concentrations were 13
percent lower in 2010 than in 2001. This decline
is largely due to reductions in oxides of nitrogen
(NOx) emissions required by EPA rules including
the NOx State Implementation Plan (SIP) Call,
preliminary implementation of the Clean Air
Interstate Rule (CAIR), and Tier 2 Light Duty
Vehicle Emissions Standards.
Despite clean air progress, approximately 124
million people lived in counties that exceeded
one or more national ambient air quality standard
(NAAQS) in 2010, as shown in Figure 1. Ground-
level ozone and particle pollution still present
challenges in many areas of the country.
Levels of Many Toxic Air Pollutants
Have Declined
Total emissions of toxic air pollutants have
decreased by approximately 42 percent between
1990 and 2005. Control programs for mobile
sources and facilities such as chemical plants, dry
cleaners, coke ovens, and incinerators are primarily
responsible for these reductions.
Ozone (8-houi)
PM,5 (annual and/or 24-hour)
PM,0 (24-hour)
Lead (3-month)
NO. (annual)
CO (8-hour)
SO. (annual and/or 24-hour)
One or more NAAQS
108.0
6.0
17.3
20.2
0.0
0.0
16,7
123.8
I I j [
20 40 60 80
Millions of People
Figure 1. Number of
people (in millions)
living in counties
with air quality
concentrations above
the level of the primary
(health-based) National
Ambient Air Quality
Standards (NAAQS) in
2010.
Note: Projected population
data for 2009 (U.S. Census
Bureau, 2009). Ozone (8-hour)
is based on the 2008 revised
ozone NAAQS of 0.075 ppm. The
revised 1-hour standards for NO2
and SO2 are not included.
100
120
140
Our Nation's Air
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Highlights
Monitored concentrations of toxic pollutants
such as benzene, 1,3-butadiene, ethylbenzene,
and toluene decreased by 5 percent or more per
year between 2003 and 2010 at more than half
of ambient monitoring sites. Other toxic air
pollutants of concern to public health such as
carbon tetrachloride, formaldehyde, and several
metals, declined at most sites.
Air Quality and Greenhouse Gases
EPA has concluded that there is compelling
evidence that many fundamental measures of
climate in the United States (e.g., air temperature)
are changing, and many of these changes are linked
to the accumulation of greenhouse gases (GHGs)
in the atmosphere. GHG emissions from the U.S.
have increased by approximately 7 percent since
1990 and global GHG emissions are increasing at
an even greater rate. Among other impacts, climate
change also contributes to worsening air quality
that can endanger public health.
While reductions in emissions of long-lived
GHGs like CO2 will be essential for addressing
climate change in the long term, there are also
climate benefits associated with reductions in
certain short lived pollutants. In addition to known
health benefits, reductions in black carbon particle
pollution and ozone are also likely to lead to
climate benefits.
More Improvements Anticipated
EPA expects air quality to continue to improve as
recently adopted regulations are fully implemented
and states work to meet current and recently revised
national air quality standards. Key regulations
include the Locomotive Engines and Marine
Compression-Ignition Engines Rule, the Tier 2
Vehicle and Gasoline Sulfur Rule, the Heavy-Duty
Highway Diesel Rule, the Clean Air Non-Road Diesel
Rule, the Mobile Source Air Toxics Rule, the Cross
State Air Pollution Rule and the Mercury and Air
Toxics Standards.
Our Nation's Air
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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; (2) decreased
lung function; (3) increased frequency and severity of
respiratory symptoms such as difficulty breathing and
coughing; (4) increased susceptibility to respiratory
infections; (5) effects on the nervous system, including
the brain, such as IQJoss and impacts on learning,
memory, and behavior; (6) cancer; and (7) 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., heart failure/ischemic heart disease, asthma,
emphysema, and chronic bronchitis), diabetics, older
adults, and children.
Air pollution also damages our environment. For
example, ozone can damage vegetation, adversely
impacting the growth of plants and trees. These impacts
can reduce the ability of plants to uptake carbon
dioxide (CO2) from the atmosphere and indirectly
affect entire ecosystems.
Sources and Health Effects of Air Pollution
Pollutant Sources
Secondary pollutant typically formed by chemical
Ozone [OJ reaction of volatile organic compounds (VOCs)
and NO^ in the presence of sunlight.
Health Effects
Decreases lung function and causes respiratory symptoms, such
as coughing and shortness of breath; aggravates asthma and
other lung diseases leading to increased medication use, hospital
admissions, emergency department (ED) visits, and premature
mortality.
Particulate
Matter (PM)
Emitted or formed through chemical reactions; fuel
combustion (e.g., burning coal, wood, diesel);
industrial processes; agriculture (plowing, field
burning); and unpaved roads.
Short-term exposures can aggravate heart or lung diseases leading
to respiratory symptoms, increased medication use, hospital
admissions, ED visits, and premature mortality; long-term exposures
can lead to the development of heart or lung disease and
premature morta ity.
Lead
Smelters (metal refineries) and other metal
industries; combustion of leaded gasoline in piston
engine aircraft; waste incinerators; and battery
manufacturing.
Damages the developing nervous system, resulting in IQ loss
and impacts on learning, memory, and behavior in children.
Cardiovascular and renal effects in adults and early effects related
to anemia.
Oxides of
Nitrogen
(NO)
Fuel combustion (e.g., electric utilities, industrial
boilers, and vehicles) and wood burning.
Aggravate lung diseases leading to respiratory symptoms, hospital
admissions, and ED visits; increased susceptibility to respiratory
infection.
Carbon
Monoxide
(CO)
Fuel combustion (especially vehicles).
Reduces the amount of oxygen reaching the body's organs and
tissues; aggravates heart disease, resulting in chest pain and other
symptoms leading to hospital admissions and ED visits.
Sulfur
Dioxide
(SO.)
Fuel combustion (especially high-sulfur coal);
electric utilities and industria processes; and natura
sources such as vo canoes.
Aggravates asthma and increased respiratory symptoms.
Contributes to particle formation with associated health effects.
Our Nation's Air
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Air Pollution
Sources of Air Pollution
Air pollution consists of gas and particle contaminants
that are present in the atmosphere. Gaseous pollutants
include SO2, NOx , ozone, CO, volatile organic
compounds (VOCs), certain toxic air pollutants, and
some gaseous forms of metals. Particle pollution (PM2 5
and PM10) includes a mixture of compounds. The
majority of these compounds can be grouped into five
categories: sulfate, nitrate, elemental (black) carbon,
organic carbon, and crustal material.
Some pollutants are released directly into the
atmosphere. Other pollutants are formed in the air.
Ground-level ozone forms when emissions of NO
X
and VOCs react in the presence of sunlight. Similarly,
some particles are formed from other directly emitted
pollutants. For example, sulfate particles are formed
from complex reactions in the atmosphere of SO2
emissions from power plants and industrial facilities.
Weather plays an important role in the formation of
secondarily formed air pollutants, as discussed later in
the Ozone and Particle Pollution sections.
EPA and states track direct emissions of air pollutants
and emissions that contribute to the formation of
key pollutants, 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.
Generally, emissions come from large stationary fuel
combustion sources (such as electric utilities and
industrial boilers), industrial and other processes
(such as metal smelters, petroleum refineries, cement
kilns, manufacturing facilities, and solvent utilization),
and mobile sources including highway vehicles and
non-road sources (such as recreational and construction
equipment, marine vessels, aircraft, and locomotives).
Sources emit different combinations of pollutants.
For example, electric utilities release SO2, NOx , and
particles.
Figure 2 shows the distribution of national total
emissions estimates by source category for specific
pollutants in 2010. Electric utilities contribute over
60 percent of national SO2 emissions. Agricultural
operations (included in the "other processes" category)
contribute over 80 percent of national NH3 emissions.
Almost 50 percent of the national VOC emissions
originate from solvent use (included in the "other
processes" category). Highway vehicles and non-road
mobile sources together contribute approximately 60
percent of national CO emissions. Pollutant levels
differ across regions of the country and within local
areas, depending on the size and type of sources
present.
Direct PM
Direct PM
40 60
Percent of Emissions
80
100
Source Category
Stationary Industrial and Highway Non-Road
Fuel Combustion Other Processes Vehicles Mobile
Figure 2. Distribution of national total emissions estimates by source category for specific pollutants, 2010.
Note: Lead emissions estimates are for 2008.
Our Nation's Air
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Air Pollution
Tracking Pollutant Emissions
Since 1990, national annual air pollutant emissions
have declined, with the greatest percentage drop in
lead emissions. Direct PM2 5 emissions have declined
by more than half; PM10 and SO2 emissions have
declined by more than 60 percent, and NOx and VOC
emissions have declined by more than 40 percent.The
combined emissions of the six common pollutants
and their precursors (PM2 5 and PM10, SO2, NOx ,
VOCs, CO, and lead) dropped 59 percent on average
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 were
achieved through regulations, voluntary measures taken
by industry, partnerships between federal, state, local,
and tribal governments; academia; industrial groups;
and environmental organizations. This environmental
progress has occurred while overall, the U.S. economy
grew 65 percent, Americans drove 40 percent more
miles, and population and energy use increased by 24
and 15 percent respectively. There was a noticeable
decline in Gross Domestic Product between 2008 and
2009. There was also a notable reduction in vehicle
miles traveled and energy consumed from 2007 to
2009. Factors likely contributing to these reductions
include the nationwide spike in gasoline prices during
2008 and the economic recession that began in
2008. These indicators showed an increase in 2010.
Figure 3 also shows total CO2 emissions increasing by
about 8 percent from 1990 to 2009 (http://epa.gov/
climatechange/emissions/usinventoryreport.html).
ross Domestic Product
Aggregate Emissions
(Six Common Pollutants)
I I
95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10
Figure 3. Comparison of growth measures and emissions, 1990-2010.
Note: CO, emissions estimates are from 1990 to 2009.
Our Nation's Air
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The Clean Air Act requires EPA to set national air
quality standards for specific pollutants to safeguard
human health and the environment. These standards
define the levels of air quality that EPA determines
are necessary to protect against the adverse impacts
of air pollution based on scientific evidence. EPA has
established standards for six common air pollutants,
which are referred to as "criteria" pollutants: ozone (O3),
particle pollution (PM), lead (Pb), nitrogen dioxide
(NO ), carbon monoxide (CO), and sulfur dioxide
(S02).
Trends in National Air Quality
Concentrations
Air quality has improved continuously across the U. S.
since the Clean Air Act was amended more than two
decades ago. The downward trend in air pollution has
been especially evident over the past several years as
shown in Figure 4. The record-low air pollution levels
observed in 2009 were primarily the result of numerous
national and local regulations that have sharply
reduced emissions. Also, meteorological conditions
favorable to lower air pollution levels and the economic
slowdown likely also contributed to the relatively clean
conditions in 2009. This downward trend in air quality
concentrations is expected to have had profound health
benefits for the American people.
Figure 4 shows the national trend in lead and the
national trends in the other five criteria pollutants
between 1990 and 2010, relative to their respective
40%
20% -
650%
Jvlost Recent
National Standard
Most Recent
National Standard
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10
Ozone. 507 monitors (4* maximum 8-hour average)
PM, v 632 monitors (98lh percentile 24-hour average I
PM,,, 632 monitors (annual average)
PM,3, 279 monitors (2M maximum 24-hour average)
NO,, 150 monitors (annual average)
CO, 170 monitors <2n'' maximum 8-hour average)
SO,. 229 monitors (annual average)
Lead. 62 monitors (maximum 3-month average)
Figure 4. Comparison of national levels of the six common pollutants
to the most recent national ambient air quality standards, 1990-2010.
National levels are averages across all monitors with complete data for
the time period. Note: Air quality data for PM2.5 start in 1999.
Our Nation's Air
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Six Common Pollutants
national ambient air quality standards. As noted above,
most pollutants show a steady decline throughout that
time period. For lead, there are significant year-to-
year changes in lead concentrations largely driven by
changes in lead concentrations at monitoring sites near
stationary sources. These year-to-year changes reflect
changes in operating schedules and plant closings. For
ozone and particle pollution shown in Figure 4, the
trends exhibit an even sharper decline over the past
three to five years although meteorological conditions
favorable to higher levels of ozone and particle
pollution likely contributed to higher levels in 2010
compared to 2009.
Air Quality in Nonattainment
Areas
EPA works collaboratively with state, local, and tribal
agencies to identify areas of the U.S. that do not meet
the national ambient air quality standards (NAAQS).
These areas, known as nonattainment areas, must
develop plans to reduce air pollution and attain the
NAAQS. EPA tracks the progress these areas make to
assure air quality continues to improve in places where
improvements are most needed.
Consistent with national averages, air quality in
nonattainment areas has also improved. As of 2010,
there were no violations of the annual standards for
CO, NO2, and SO2. Figure 5 shows trends in average
concentrations of ozone and particle pollution only in
existing nonattainment areas with air quality exceeding
one or more of these standards in 2010. Although
many areas exceeded the level of the standard in 2010,
there have been improvements in the levels of these
pollutants in nonattainment areas since 2001. For
example, between 2001 and 2010, ozone nonattainment
areas showed a 9 percent improvement in ozone
concentration levels. Figure 5 does not include all areas
that are designated nonattainment for the pollutant
shown. For more information on areas designated as
nonattainment visit www.epa.gov/airquality/greenbook.
Despite these improvements, further reductions in air
pollution are needed over parts of the country. EPA
expects air quality to continue to improve as recent
regulations are fully implemented and new measures
are finalized. EPA periodically reviews and revises
the national air quality standards as needed to protect
public health and the environment. This means
that although there is clear progress in reducing air
pollution, and we expect that trend to continue, there
may be a need to implement further control measures
to meet new more protective air quality standards.
'5
CL
'5
E
f 0.115-
E " Ij~r
5g 0.105
I 1
Figure 5. Air quality trends in nonattainment areas exceeding the ozone and particle pollution standards in 2010.
Our Nation's Air
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Six Common Pollutants
Trends in Unhealthy Air Quality
Days
The Air Quality Index (AQI) relates daily air
pollution concentrations for ozone particle pollution,
NO2, CO, and SO2 to health concerns for sensitive
groups and for the general public. A value of 100
generally corresponds to the national air quality
standard for each pollutant. Values below 100
are considered satisfactory. Values above 100 are
considered unhealthy first for certain sensitive
groups of people, then for everyone as the AQI values
increase.
Figure 6 shows the number of days on which the
AQI exceeded 100 for each of the past nine years at
35 select metropolitan areas. All areas experienced
fewer unhealthy days in 2010 compared to 2002.
Ozone and particle pollution are the primary
contributors to unhealthy AQI days. Weather
conditions, as well as emissions, contribute to ozone
EPA's Air Quality Index (AQI)
Air Quality Index Levels of Health Concern
{AQI) Values
OtoSO Good
51-COO
I CM-ISO
Unlwalihp tor Smarre Groupi
AIR QUALITY INDEX
http://www.airnow.gov
and particle pollution formation. Some areas in the
eastern U.S. experienced more unhealthy days in 2010
compared to 2009, mostly due to weather conditions
being more conducive to ozone formation in these areas
in 2010.
J
32
22 ft.
Philadelphia
Cleveland
_
_ 13* Nashville
lemphis
AJh- -
Birmingham Atlanta
^m^^^m
2002 2003 2004 2005 2006 2007 2008
Figure 6. Number of days on which AQI values were greater than 100 during 2002-2010 in selected cities.
Our Nation's Air
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Trends in Ground-Level Ozone
Concentrations
In March 2008, EPA strengthened the national
standards for ground-level ozone, setting an 8-hour
standard at 0.075 parts per million (ppm). Nationally,
average ground-level ozone concentrations were 13
percent lower in 2010 than in 2001, as shown in
Figure 7. The trend showed a notable decline after
2002. When comparing the three-year periods 2001-
2003 and 2008-2010, approximately 82 percent of
the monitoring sites recorded a significant decline
(> 0.005 ppm) in ozone concentrations. Sites that
showed the greatest improvement were in or near the
following metropolitan areas: South Bend, IN; Buffalo,
NY; Chicago, IL; Milwaukee, WI; and Cleveland,
OH. Ozone trends can vary locally. One site may
show increases in ozone levels while nearby sites show
decreases.
Ozone
Figure 8 shows a snapshot of ozone concentrations in
2010. The highest ozone concentrations occurred in
California. Note that the high concentration levels in
Utah occurred in winter. Elevated wintertime ozone
concentrations are most likely to occur when local
sources of NOx and VOC emissions are trapped in a
snow-covered valley on a clear day with light winds.
Nationally, approximately 24 percent of all sites
measured concentrations above the standard of 0.075
ppm on four or more days in 2010.
Over the years, EPA has adopted a number of
regulations that helped reduce ozone levels
nationwide. Other recently adopted regulations
will help to continue to make progress toward
lower, healthier ozone levels. These regulations
include:
Coordinated steps to reduce power plant
pollution
» NOx State Implementation Plan (SIP) Call
» Acid Rain Program
» Cross-State Air Pollution Rule (CSAPR)
Requiring other stationary sources to reduce
pollution
» Aerosol, architectural, autobody, and
miscellaneous coatings
» Consumer products
» Regional haze requirements
Limiting emissions from mobile sources
» Light Duty Tier 2 Rule - new cars, SUVs,
trucks and vans
» Heavy-Duty Diesel Rule on and nonroad
» Requirements for marine vehicles, and
locomotives
On December 30, 2011, the D.C. Circuit Court
stayed the CSAPR rule pending judicial review.
This decision delays implementation of CSAPR
and leaves the Clean Air Interstate Rule in place
pending the court's decision.
u. I/L -
-£ 0'1-
Q.
S; 0.08 -
o
'it 0.06-
=
8 0.04 -
0 0.02 -
n -
984 sites
Average go percent of sjtes are be|OW thjs |jne
I
""" -^
Current National Standard (revised 2008)
1
10 percent of sites are below this line.
Figure 7. National 8-hour ozone air quality
trend, 2001-2010 (average of annual fourth
highest daily maximum 8 hour concentrations
in ppm).
01 02 03 04 05 06 07 08
2001 to 2010: 13% decrease
09 10
Our Nation's Air
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Ozone
Concentration Range (ppm)
0.025-0.059(81 Sites)
O 0.060-0.075 (835 Sites)
O 0,076 - 0.095 (279 Sites)
0.096-0.120 (18 Sites)
Puerto Rico
Alaska
Figure 8. Ozone concentrations in ppm, 2010 (fourth highest daily maximum 8-hour concentration).
Our Nation's Air
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Ozon e
Weather Influences Ozone
In addition to precursor emissions, weather 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
remain unchanged. To better evaluate the progress and
effectiveness of ozone precursor emission reduction
programs, EPA uses a statistical model to estimate the
influence of weather on ozone formation.
Figure 9 shows trends in average seasonal ozone levels
from 2001 through 2010 across 180 selected sites,
before and after adjusting for weather-related effects.
For example, the summer of 2009 was characterized
by cooler than normal conditions across much of
the Eastern U.S., which contributed to less ozone
formation and resulted in an upward adjustment to the
ozone trend. By contrast, hot and dry conditions in the
Eastern U.S. during the summer of 2010 contributed
to more ozone formation, resulting in a downward
adjustment to the ozone trend.
Both the observed and adjusted ozone trends are
characterized by a large decrease in ozone in the
Eastern U.S. between 2002 and 2004. This abrupt
decline in ozone levels coincides with the large
reduction in NOx emissions brought about by EPA's
NOx SIP Call program which began in 2003 and was
fully implemented in 2004. Removing the effects of
weather confirms that ozone levels have continued to
improve across the U.S. in recent years due to emission
reduction programs.
National Trend
180 Sites
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| 0.060:
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v 0.050:
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£j 0.045:
0.0401
0
r " "-
^^
2001 to 2010:
2001 to 2010:
1 02 03
>»--»--^
^^ ^
9% decrease (observed)
14% decrease (adjusted)
04 05 06 07 08 09 1
Western U.S. Trend
38 Sites
»*coici M w.o. iicnu ou onco easiern u.o. rena <*z ones
0 O/S"1 ' rt rt"*e
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c 0.065 :
a
| 0.060:
| 0.055:
e 0.050^
N 0.045:
0 040 n
- ^
^ *- -»" ~*-^
»
2001 to 2010: 7% decrease (observed)
2001 to 2010: 6% decrease (adjusted)
u.ur 3:
1 0.070-;
Q. 1
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o
1 0.060:
| 0.055-
' 0
a 0.050-
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r ^^ ,*~~. ~-*^
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2001 to 2010: 10% decrease (observed) ^^ ^
2001 to 2010: 16% decrease (adjusted)
U.UHU-I 1 p 1 1 1 1 1 1 1
01 02 03 04 05 06 07 08 09 10 01 02 03 Q4 05 Q6 Q7 og ng 1
» Observed trend Adjusted trend
Figure 9. Trends in average summertime daily maximum 8-hour ozone concentrations in ppm (May-September), before
and after adjusting for weather nationally, in western states, and in eastern states, (and the location of monitoring sites
used in the averages).
1 1
Our Nation's Air
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Particle Pollution
EPA has set national standards to protect against the
health and welfare effects associated with exposure to
fine and coarse particles. Fine particles are generally
considered to be less than or equal to 2.5 micrometers
(|im) in aerodynamic diameter, or PM25. Coarse
particles are those between 2.5 and 10 |im in diameter.
PM1(| is the indicator used for the coarse particle
standard.
Trends in PM25 Concentrations
There are two national air quality standards for
PM25: an annual standard (15 |ig/m3) and a 24-hour
standard (35 |ig/m3). Nationally, annual and 24-hour
PM2 5 concentrations declined by 24 and 28 percent,
respectively, between 2001 and 2010, as shown in
Figure 10.
"5)
Annual -B
0)
o
c
o
O
20
18
16
14-
12 :
10-
8
6-
4-
2
0
90 percent of sites are below this line. 686 sites
Current National Standard
Average
10 percent of sites are below this line.
01 02 03 04 05 06 07 08 09 10
2001 to 2010: 24% decrease
wiv
45 -
IT 40-
C
o 05
"^ 30-
24-hour § 25 -
£ 20-
s "" ^^^
Average
f
10 percent of sites are below this line.
01 02 03 04 05 06 07 08
2001 to 2010: 28% decrease
09
10
Figure 10. National PM2 5 air quality trends, 2001-2010 (annual average concentration
and 98th percentile of 24-hour concentration in ug/m3)-
Our Nation's Air
1 2
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Particle Pollution
In 2010, the highest annual average PM25
concentrations were in California, Indiana,
Pennsylvania and Hawaii, as shown in Figure 11.
The highest 24-hour PM2 5 concentrations were in
California and Alaska.
Some sites showed high 24-hour PM25 concentrations
but low annual PM25 concentrations. Sites that show
high 24-hour concentrations but low or moderate
annual concentrations exhibit substantial variability
from season to season. For example, sites in the
Northwest generally show 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 the annual PM2 5 standard, as indicated by
yellow and red dots on the maps below. Of the 6 sites
that exceeded the annual standard and 43 sites that
exceeded the 24-hour standard, 4 sites exceeded both.
Annual
Concentration Range (pg/m3)
3.1-12.0 (680 Sites)
O 12.1 - 15.0(148 Sites)
O 15.1-18.0 (5 Sites)
18.1 -225(1 Site)
Puerto Rico
Figure 11. Annual average and
24-hour (98th percentile of 24-hour
concentrations) PM2 5 concentrations in
ug/m3, 2010.
24-hour
Concentration Range (pg/m3)
6- 15 (87 Sites)
O 16-35 (704 Sites)
O 36-55 (42 Sites)
55-56(1 Sile)
Puerto Rico
1 3
Our Nation's Air
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Particle Pollution
Weather Influences PM
2.5
In addition to emissions, weather plays an important
role in the formation of PM2 5. PM2 5 tends to be
dominated by different components at different times
of the year (e.g. sulfates in the summer and nitrates in
the winter), so the statistical model adjusting the PM25
trend for weather is split into a 'warm months' trend
running from May to September and a 'cool months'
trend encompassing the remaining months of the year.
The two trends were combined to form the annual
trend using a weighted average.
Figure 12 shows trends in PM25 from 2001 to 2010,
averaged across 145 selected sites before and after
adjusting for weather. The warm months trend is
characterized by a large decrease in average PM2 5
between 2008 and 2010, while the cool months trend
shows a slow but steady decrease in PM2 5 over the past
decade. Overall, average PM25 concentrations in the
U. S. have declined steadily since 2005 after removing
the effects due to weather indicating improvement
based on recently enacted emissions reduction
programs.
18
16
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Annual Trend
145 Sites
N
2001 to 2010: 24% decrease (observed)
2001 to 2010: 24% decrease (adjusted)
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2001 to 2010: 21% decrease (adjusted)
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29% decrease
145 Sites
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(adjusted) \-
01 02 03 04 05 06 07 08 09 10
Observed trend
01 02 03 04 05 06 07 08 09 10
Adjusted trend
Figure 12. Trends in annual, cool-month (October-April) and warm-month (May-September) average PM25 concentrations
in ug/m3 (before and after adjusting for weather), and the location of monitoring sites used in the average.
Our Nation's Air
1 4
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Particle Pollution
Trends in PIVL Concentrations
'10
Nationally, 24-hour PM10 concentrations declined
by 29 percent between 2001 and 2010, as shown in
Figure 13.
Figure 14 shows that in 2010, the highest PM10
concentrations were located in California, Utah,
Colorado and New Mexico. However, within these
same states some sites showed a decline greater than
50 |ig/m3. Highest concentrations are largely located
in dry and/or industrial areas with a high number of
coarse particle sources.
160
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Trends in Lead
Concentrations
Concentrations of lead decreased
approximately 71 percent between 2001
and 2010, as shown in Figure 15. Average
concentrations are shown for 39 sites near
large stationary sources and 63 sites that
are not near stationary industrial sources.
The typical average concentration near a
stationary source (e.g., metals processors,
battery manufacturers, and mining
operations) is approximately eight times the
typical concentration at a site that is not
near a stationary industrial 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, national
lead concentrations declined between
2001 and 2002, mostly due to lower lead
concentrations at sites in Herculaneum,
MO.
Figure 16 shows lead concentrations in
2010. Of the 196 sites shown, 34 sites
exceeded the 2008 lead standard (0.15 |ig/
m3). All of these sites are located near
stationary lead sources. Also in 2010, EPA
promulgated requirements for monitoring
near additional stationary lead sources
that are estimated to have 0.50 or more
tons per year (tpy) lead emissions. Up to
270 new locations will be monitoring lead
concentrations by the end of 2011 as a result
of changes to the monitoring requirements
made in 2008 and 2010.
National Avg. (102 Sites)
Source Oriented Avg. (39 Sites)
Non-Source Oriented Avg. (63 Sites)
N
tcurrent National Standard (revised 2008)
01 02 03 04 05 06 07 08
2001 to 2010: 71% decrease
09
10J
Figure 15. National lead air quality trend, 2001-2010 (maximum
3-month average in u.g/m3).
Note: 90 percent of sites are shown in the orange area.
Concentration Range {|jg/m3
0.00-007 (140 Sites)
O 0.08-0.15 (22 Sites)
0.16-1.37 (34 Sites)
.**
Puerto Rico
Figure 16. Lead concentrations in ug/m3, 2010 (maximum 3-month
averages).
Note: The number of sites in Figure 15 (102) differs from the number of sites in Figure 16 (196) due
to differences in the requirements for lead data to be considered complete for each figure
Our Nation's Air
1 6
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ttn-vrai-
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Trends in NO2, CO, and SO2
Concentrations
Nationally, annual mean concentrations of
NO2 decreased 33 percent between 2001
and 2010, as shown in Figure 17. In 2010,
NO2 concentrations were the lowest of the
ten-year period. All recorded concentrations
were well below the level of the annual
standard (53 ppb).
Nationally, concentrations of 8-hour CO
decreased 52 percent between 2001 and
2010, as shown in Figure 18. In 2010, CO
concentrations were the lowest in the past
ten years. All concentrations were below
the 8-hour standard (9 ppm) and 1-hour
standard (35 ppm).
Nationally, annual mean concentrations of
SO2 decreased 50 percent between 2001
and 2010, as shown in Figure 19. In 2010,
annual SO2 concentrations were the lowest
of the ten-year period. One site in Hawaii
showed concentrations above the level of
the annual standard (30 ppb) and four sites
in Hawaii showed concentrations above the
level of the 24-hour standard (140 ppb).
These high measurements were probably
caused by emissions from a nearby volcano.
Downward trends in annual 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 annual standards,
EPA continues to track these pollutants
because of their contribution to other air
pollutants (e.g., ozone and PM25) and
reduced visibility. On August 12,2011,
EPA finalized the decision to retain existing
primary CO standards.
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Current National Annual Mean Standard
90 percent of sites are below this line.
i
10 percent of sites are below this line.
01 02 03 04 05 06 07 08
2001 to 2010: 33% decrease
09
10
Figure 17. National NO2 air quality trend, 2001-2010
(annual average in ppm).
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7-
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Current National Standard
Average
90 percent of sites are below this line.
I
10 percent of sites are below this line
01 02 03 04 05 06 07 08
2001 to 2010: 52% decrease
09 10
Figure 18. National CO air quality trend, 2001-2010
(second maximum 8-hour average in ppm).
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347 sites
Current National Annual Mean Standard
90 percent of sites are below this line.
Average
10 percent of sites are below this line.
01 02 03 04 05 06 07 08
2001 to 2010: 50% decrease
09 10
Figure 19. National SO2 air quality trend, 2001-2010
(annual average in ppm).
1 7
Our Nation's Air
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NO, CO, SO
2010 NO2and SO2 Standards
On January 22,2010, EPA strengthened the health-
based NAAQS for NO2. This action did not impact the
NO2 secondary standard, set to protect public welfare.
EPA set the new 1-hour NO2 standard at the level
of 100 ppb. The form for the 1-hour NO2 standard
is the 3-year average of the 98th percentile of the
annual distribution of daily maximum 1-hour average
concentrations. EPA also retained, with no change,
the current annual average NO2 standard of 53 ppb.
Although this new standard is a 3-year average, Figure
20 shows a snapshot of the 98th percentile of the
1-hour daily maximum NO2 concentration for 2010
only.
On June 2,2010, EPA strengthened the health-based
NAAQS for SO2. This action did not impact the
SO2 secondary standard, set to protect public welfare,
which is currently under review. EPA replaced the
existing annual and 24-hour primary SO2 standards
with a new 1-hour SO2 standard set at 75 ppb to better
protect public health by reducing exposure to high
short-term (5 minutes to 24 hours) concentrations
of SO2. Although this new standard is based on a
3-year average, Figure 21 shows a snapshot of the
99th percentile of the daily 1-hour maximum SO2
concentration for 2010 only. Note that Figure 21
shows that the highest daily 1-hour maximum SO2
concentrations occurred at sites in the Upper Midwest
and portions of the Northeastern U.S.
On July 12, 2011, EPA proposed action on the
combined review of the secondary NAAQS for
oxides of nitrogen (NOx) and oxides of sulfur (SOx).
EPA sets secondary standards to protect against
environmental damage caused by certain air
pollutants. Consistent with the scientific evidence
pointing to the interrelated impacts of NOx and SOx
on plants, soils, lakes, and streams, EPA assessed the
environmental effects of these pollutants together.
Based on this scientific evidence, EPA is proposing
to retain the existing secondary standards for NOx
and SOx. The existing secondary standards are:
NO2: 53 ppb (parts per billion) averaged over
a year; and
SO2: 0.5 ppm averaged over three hours, not
to be exceeded more than once per year.
Also, EPA is proposing to establish an additional set
of secondary standards identical to the new health-
based primary standards the Agency set in 2010.
The proposed new secondary standards would be:
For NO2:100 ppb (parts per billion) averaged
over one hour; and
For SO2: 75 ppb averaged over one hour.
For additional information on the proposed
secondary standards visit www.epa.gov/air/
nitrogenoxides/actions.html.
Concentration Range (ppb)
5-50(198 Sites)
O 51-75 (97 Siles)
O 76-100(1 She)
> 10010 SMI
Figure 20. NO2 concentrations in ppb, 2010 (98th
percentile of daily 1-hr maximum).
Note: Typically the 1-hour standard is determined as the three-year average of
the 98th (NO2) or 99th (SO2) percentile of the daily maximum 1-hour average;
however, these maps only include one year (2010).
Concentration Range (ppb)
1 25 1184 Sites)
O 26-50 (83 Sites)
O 51 - 75 (46 Sites)
76-314 (47 Sites)
> 75 (57 Sites)
Figure 21. SO2 concentrations in ppb, 2010 (99th
percentile of daily 1-hr maximum).
Our Nation's Air
1 8
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utants
Trends in Toxic Air Pollutant
Concentrations
Under the Clean Air Act, EPA regulates 187 toxic air
pollutants. Toxicity levels, or the potential for adverse
effects on human health and the environment, 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. EPA recommends a set of benchmark toxicity
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.
EPA frequently relies on modeling studies to
supplement air toxic monitoring data and 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 plus diesel
particulate (assessed for noncancer only). NATA
examines individual pollutant effects as well as
cumulative effects on human health.
Figure 22 shows the estimated lifetime cancer risk
across the continental U.S. by census tract based on
2005 NATA model estimates. The national average
cancer risk level in 2005 is 50 in a million. Many urban
areas as well as transportation corridors show a risk
above the national average. From a national perspective,
formaldehyde and benzene are the most significant
toxic air pollutants for which EPA could estimate
cancer risk. These toxic air pollutants contributed
nearly 60 percent of the average individual cancer risk
identified in the 2005 assessment. In addition to the
census tract level ambient concentrations predicted by
the NATA 2005, EPA also used the model to compare
with monitored air toxics concentrations at over
1000 locations. When comparing modeling results
to monitored data, a model-to-monitor ratio close to
1 for a particular toxic pollutant at a monitoring site
indicates a high level of confidence in the modeling
results for that toxic pollutant and monitoring site.
Good agreement was seen between the model and
monitors for the following pollutants: acetaldehyde,
arsenic (PM2.5), benzene, carbon tetrachloride,
formaldehyde, methyl chloride and toluene. Results
Mean Risk Level
7 - 25 in a million
26 - 50 in a million
^| 51 - 75 in a million
^B 76 - 100 in a million
I 101 - 288 in a million
Figure 22. Estimated
census-tract cancer
risk from the 2005
National-Scale Air
Toxics Assessment
(NATA2005). Darker
colors show greater
cancer risk associated
with toxic air pollutants.
Puerto Rico
Alaska
1 9
Our Nation's Air
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Toxic Air Pollutants
of this model-to-monitor comparison can be found at
http://www.epa.gov/ttn/atw/nata2005/compare.html.
Though not included in the figure below, 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. For more information on
NATA visit http://www.epa.gov/ttn/atw/natamain.
Since 2003, EPA, working with state and local partners,
has nationally monitored air toxic pollutants through
the National Air Toxics Trends Station (NATTS)
program. 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, hexavalent chromium, and polycyclic
aromatic hydrocarbons [PAHs] such as napthalene)
in order to establish overall trends. During 2010, data
were collected every one in six days at 27 NATTS sites
as shown in Figure 23 (20 urban and 7 rural) for PM10
metals, VOCs, carbonyls, hexavalent chromium, and
PAHs. In addition to the NATTS program, about 300
monitoring sitesoperated by state, local, and tribal
agenciesare currently collecting data to help track
toxic air pollutant levels across the country. For more
information on NATTS visit http://www.epa.gov/ttn/
amtic/natts. html.
Figure 24 shows the trends from 2003 to 2010 in
ambient monitoring levels for some of the important air
toxic air pollutants. When the median percent change
per year (marked by an x for each pollutant shown)
is below zero, the majority of sites in the U.S. show
a decrease in concentrations. Ambient monitoring
data show that some of the toxic air pollutants of
greatest widespread concern to public health, such
as benzene, 1,3-butadiene, formaldehyde and several
metals, are declining at most sites. Monitoring data
shown in Figure 24 represent compilation of data from
monitoring sites nationwide including data from the
NATTS sites. Pollutants represented have at least
a minimum of 40 valid trends sites with 35 percent
of the data being measured at levels above monitor
detection limits. Some pollutants which are more
widely monitored such as lead and manganese may
include data from several hundred sites which meet
the 35 percent criteria. Some pollutants such as methyl
Monitoring Location
rural
A urban
Puerto Rico
Alaska
Figure 23. National Air Toxics Trends Sites (NATTS)
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Toxi c Air Pollutants
tert-butyl ether (MTBE) whose use was discontinued
after 2006 are no longer being measured at ambient
monitoring sites as the levels are very low. There are
two chlorinated VOCs which appear to have increased
slightly, dichloromethane (methylene chloride) which is
commonly used as a solvent, and chloromethane which
was once used as a refrigerant and is also naturally
formed in the oceans.
Carbon Tetrachlccide
Chief omethane
Dichloromethane
1.3-Butadiene
2,2.4-Trimethylpentane
Benzene
Ethylbenzene
n-Hexane
o-Xylene
Slyrene
Toluene
Acetaldehyde
Formaldehyde
Pt opian aldehyde
Arsenic PM2.5
Lead PM2.5
Manganese PM25
Nickel PM2.5
Chlorinated VOCs
X
Hydrocarbons
Oxygenated VOCs
Metals
r
-15 -10 -5 0 5 10
Percentage Change per Year
Median Percentage
C I icinge per Year
!Uth X . 901h
Percentile Percentile
Assessing Outdoor Air Near Schools
In March 2009, EPA released a list of schools
that would be part of an initiative to understand
whether outdoor toxic air pollution poses health
concerns to schoolchildren. The monitoring
took place at 65 schools in 22 states and 2 tribal
areas. EPA selected the schools using a number of
factors, including results from computer modeling
analyses - the 2002 NATA, results presented in
a newspaper series on air toxics at schools, and
in consultation with state and local air agencies.
The pollutants monitored varied by school. EPA
identified pollutants to measure at each school
based on the best available information about the
pollution sources, potential airconcentrations, and
risk in each area. Initial monitoring was completed
for all schools in May 2010. EPA posted monitoring
results after data was quality-assured and intends
to post final reports for each monitoring location
as the information is analyzed. For the majority
of schools, monitored concentrations have been
lower than EPA's models predicted. However,
additional monitoring will be conducted for a few
schools for various reasons. As a follow on to the
schools program, EPA issued a request in 2011
for proposals for grants for community-scale air
toxics ambient monitoring projects. Through
these grants, local air toxics concerns will be
investigated by state and local agencies. For more
information, visit http://www.epa.gov/schoolair/.
Figure 24. Distribution of changes in ambient
concentrations at U.S. toxic air pollutant
monitoring sites, 2003-2010 (percent change in
annual average concentrations).
2 1
Our Nation's Air
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an
alit
Climate Change and GHG
Emissions Trends
Climate change and air pollution are closely coupled.
Just as air pollution can have adverse effects on human
health and ecosystems, it can also impact the Earth's
climate. When energy from the sun reaches the Earth,
the planet absorbs some of this energy and radiates
the rest back to space as heat. The Earth's surface
temperature depends on this balance between incoming
and outgoing energy. Atmospheric greenhouse gases
(GHGs) like carbon dioxide (CO2) and methane (CH4)
can trap this energy and prevent the heat from escaping.
In 2009, EPA issued a finding under the Clean Air
Act that GHGs constitute air pollution that threatens
public health and welfare. The science supporting
that finding allowed EPA to conclude that warming
of the climate system is unequivocal, and that most of
the observed increase in global average temperatures
since the mid-20th century is very likely due to the
anthropogenic increase in GHG concentrations
(EPA, 2009). EPA has further concluded that there is
compelling evidence that many fundamental measures
of climate in the United States are changing, and
many of these changes are linked to the accumulation
of GHGs in the atmosphere. Examples of these
climate-driven effects include warmer air and ocean
temperatures, more high-intensity rainfall events, and
more frequent heat waves.
In collaboration with other government agencies,
EPA tracks both GHG emissions (EPA, 2011) and
indicators of climate change (EPA, 2010). Figure 25
shows trends in domestic GHG emissions over the
past two decades. Total U.S. GHG emissions have
increased 7.3 percent from 1990 to 2009. The majority
of domestic GHG emissions result from electricity
generation and transportation.
In January 2012, EPA released for the first time
comprehensive greenhouse gas (GHG) emissions data
reported directly from large facilities and suppliers
across the country through the GHG Reporting
Program. The 2010 GHG data includes public
information from facilities in nine industry groups that
directly emit large quantities of GHGs (e.g., power
plants, petroleum refineries, landfills, etc.) as well
as suppliers of certain fossil fuels. EPA's online data
publication tool allows users to view and sort GHG
MFCs, PFCs, &SF6
Nitrous Oxide
Methane
Carbon Dioxide
8000
6000 -
LU
g" 4000
o>
2000 -
Figure 25. Domestic greenhouse
gas emissions in teragrams of
carbon dioxide equivalents
(Tg CO2 eq), 1990-2009.
(EPA, 2011)
Notes: A teragram is equal to 1 million
metric tons. Emissions in the figure include
fluorocarbons (MFCs, PFCs) and sulfur
hexafluoride (SF6). CO2 eq refers to the
global warming potential (GWP) of each
greenhouse gas (e.g., nitrous oxide) as
compared to the GWP of CO2 (EPA, 2011)
90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
2 2
Our Nation's Air
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data from more than 6,700 facilities in a variety of
ways; including by facility, location, industrial sector,
and type of GHG emitted. This information can
be used by communities to identify nearby sources
of greenhouse gas emissions, help businesses track
emissions and find cost- and fuel-saving opportunities,
and provide information to the finance and investment
communities. For more information, visit http://epa.
gov/climatechange/emissions/ghgdata.
Climate Impacts of Air Pollution
Conventional air pollutants such as ozone and particle
pollution can also contribute to climate change.
Because ozone and particle pollution stay in the
atmosphere for only a few days or weeks, reducing these
emissions can help reduce climate impacts in the near-
term.
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Climate Change & Air Quality
The net effect for all particles in the atmosphere is
cooling, as scattering generally dominates, though
effects can vary dramatically by region (Forster et. al.,
2007). While the health benefits of reducing all types
of emissions contributing to particle pollution are
relatively clear, the net climate impact of emissions
reduction strategies will depend on the relative
reductions in particles of different types.
Air Quality Impacts of Climate
Change
The close connection between climate and air quality
is also reflected in the impacts of climate change on
air pollution levels. As previously discussed, ozone and
particle pollution are strongly influenced by shifts in
the weather (e.g., heat waves or droughts). Based on
projected future climate scenarios, and in the absence of
additional emissions reductions, the Intergovernmental
Panel on Climate Change (IPCC) projected "declining
air quality in cities" into the future as a result of climate
change. Further, EPA concluded in 2009 that GHG
emissions "may reasonably be anticipated both to
endanger public health and to endanger public welfare."
This endangerment finding was based, in part, on the
potential for climate change to worsen air quality over
the U. S. and the accompanying public health impacts
that would result.
EPA has concluded (EPA, 2009) that climate change
could have the following impacts on national air quality
levels:
Produce 2-8 ppb increases in summertime average
ground-level ozone concentrations in many regions
of the country.
Further exacerbate ozone concentrations on days
when weather is already conducive to high ozone
concentrations
Lengthen the ozone season
Produce both increases and decreases in particle
pollution over different regions of the U.S.
Because climate represents meteorological conditions
over a long period of time, it is difficult to identify a
climate fingerprint in the current trends in air quality
discussed earlier in this report. Given the general
improvement in air quality over the past decade, it
appears that emissions reductions from air quality
regulations are outpacing any climate-driven impacts.
2 4
Our Nation's Air
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penaix
Terminology
AQI Air Quality Index
AQS Air Quality System
BC black carbon
CASTNET Clean Air Status and Trends Network
CFCs chlorofluorocarbons
CH4 methane
CO carbon monoxide
CO2 carbon dioxide
EPA U. S. Environmental Protection Agency
GHG greenhouse gas
HFCs hydrofluorocarbons
IPCC Intergovernmental Panel on Climate
Change
NAAQS National Ambient Air Quality
Standards
NAS National Academy of Sciences
NATA National-Scale Air Toxic Assessment
NATTS National Air Toxics Trends Stations
NEI National Emissions Inventory
NH, ammonia
j
NOx oxides of nitrogen
NO2 nitrogen dioxide
O ground-level ozone
PAHs polycyclic aromatic hydrocarbons
PFCs perfluorinated compounds
PM particulate matter (particle pollution)
PM2 5 particulate matter (fine) 2.5 |im or less
in size
PM1(| particulate matter 10 |im or less in size
ppb parts per billion
ppm parts per million
SF, sulfur hexafluoride
6
SIP state implementation plan
SO2 sulfur dioxide
|im micrometers (microns)
ug/m3 micrograms per cubic meter
VOCs volatile organic compounds
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Appendix
Websites
Background/General Information
Air Quality Index: http://www.airnow.gov
Air Quality System: http://www.epa.gov/ttn/airs/airsaqs/
Air Quality System Detailed Data: http://www.epa.gov/ttn/airs/airsaqs/detaildata
Health and Ecological Effects: http://www.epa.gov/air/urbanair/
National Ambient Air Quality Standards: http://www.epa.gov/air/criteria.html
National Center for Environmental Assessment: http://cfpub.epa.gov/ncea/
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
Intergovernmental Panel on Climate Change: http://www.ipcc.ch
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
2002 National-Scale Air Toxics Assessment: http://www.epa.gov/ttn/atw/nata2002/
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: 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 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
26 OurNation'sAir
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References
Highlights
U.S. Census Bureau, Population Division, Annual Estimates of the Resident Population by Selected Age Groups
and Sex for Counties: April 1, 2000 to July 1, 2008, available on the Internet at http://www.census.gov/popest/
counties/asrh/CC-EST2008-agesex.html.
Climate Change and Air Quality
Cooper, O. R. et al., 2010. Nature, 463, 344-348.
Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe,
G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric
Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
[Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)].
Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
National Academy of Sciences, National Research Council, 2005. Radiative Forcing of Climate Change:
Expanding the Concept and Addressing Uncertainties, National Academies Press, Washington, D.C., October.
U S. Environmental Protection Agency, 2009. Assessment of the Impacts of Global Change on Regional U S.
Air Quality: A Synthesis of Climate Change Impacts on Ground-Level Ozone, EPA 600-R-07-094F, Office of
Research and Development, National Center for Environmental Assessment, Research Triangle Park, NC.
U.S. Environmental Protection Agency, 2010. Climate Change Indicators in the United States, EPA 430-R-10-007,
Washington, D.C., 74pp.
U.S. Environmental Protection Agency, 2011. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-
2009, EPA 430-R-l 1-005, Washington, D.C.
OurNation'sAir 27
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