particle pollution epa report 2003

8/14/2019 Particle Pollution EPA Report 2003

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The Particle Pollution ReportCurrent Understanding of Air Quality and Emissions through 2003

United StatesEnvironmental ProtectionAgency

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National Standard

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PM2.5 Concentrations are Declining


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Printed on 100% recycled/recyclable process chlorine-free paper with 100% post-consumer fiber using vegetable-oil-based ink.


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EPA 454-R-04-002December 2004

The Particle Pollution Report

Current Understanding of Air Quality and Emissions through 2003

Contract No. 68-D-02-065Work Assignment No. 2-01

U.S. Environmental Protection AgencyOffice of Air Quality Planning and StandardsEmissions, Monitoring, and Analysis Division

Research Triangle Park, North Carolina


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Contents

Introduction ii

Major Findings 1

Understanding Particle Pollution 2Particle Pollution Is 2

Complex 2A Continuum of Sizes 2Made Up of Many Species 3Seasonal 4Both Local and Regional 8

Particle Pollution in 2003 10PM10 PM2.5 12

Looking at Trends 13PM10 National and Regional Trends 13PM2.5 National and Regional Trends 1425-year PM 2.5 Trends 16Rural Sulfate Trends 18

Explaining the Trends 20Regional PM 2.5 Trends in Three

Regions (1999-2003) 20Effect of Meteorology 21The PM 2.5 Remainder 22Control Programs 23

The Future 25Upcoming PM 2.5 Designations 26PM2.5 and Other Pollutants 26

IntroductionFrom the black puff of smoke from an old diesel bus to thehaze that obscures the view in our national parks, particlepollution affects us all. This complex pollutant is present

year-round, both in our cities and in the countryside, andit can cause health problems for millions of Americans.

EPAs national air quality standards for particle pollutionare designed to protect public health and the environment.As this report shows, we are seeing progress: levels of particlepollution are decreasing on a national scale. Yet millionsof people still live in areas of the country where particlepollution levels exceed national air quality standards. Thisharmful pollution affects not only people, but also visibility,ecosystems, and man-made materials.

EPA considers fine particle pollution its most pressing air quality problem, and the Agency is taking a number of stepsthat will reduce particle emissions and formation. Theseefforts range from EPAs Acid Rain program and regulationsreducing emissions from fuels and diesel engines, to imple-mentation of the Agencys first fine particle standards anda proposed rule to reduce particle-forming emissions frompower plants.

In this report, EPA

Explores characteristics of particle pollution in theUnited States

Analyzes particle pollution for 2003 (the most recent year of data)

Summarizes recent and long-term trends Investigates the relationship between air quality and

emissions Reviews some current programs and future prospects for

reducing particle pollution levels.

In addition, text boxes in this report present informationon more specialized areas of interest, such as the PMSupersite project, episodic events, satellite monitoring, andthe relationship of particle pollution to other air pollutants.

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Major FindingsAir Quality Improvements Particulate matter (PM) air quality has been

improving nationwide, both for PM 2.5 and PM 10 . PM 2.5 concentrations

in 2003 were the lowest since nationwide moni-toring began in 1999

have decreased 10% since 1999 are about 30% lower than EPA estimates they

were 25 years ago.

PM 10 concentrations in 2003 were the second lowest since nationwide

monitoring began in 1988 have declined 7% since 1999 have declined 31% since 1988.

In 2003, 62 million people lived in 97 U.S. coun-ties with monitors showing particle pollution levelshigher than the PM 2.5 air quality standards, thePM 10 standards, or both.

Monitored levels of both PM 2.5 and PM 10 generally

decreased the most in areas with the highestconcentrations. For example, PM 2.5 levels decreased20% in the Southeast from 1999 to 2003. TheNorthwest showed a 39% decrease in PM 10 levelsfrom 1988 to 2003.

Sources and Emissions Sulfates, nitrates, and carbon compounds are the

major constituents of fine particle pollution.Sulfates and nitrates form from atmospheric trans-formation of sulfur dioxide and nitrogen oxidegases. Carbon compounds can be directly emitted,or they can form in the atmosphere from organicvapors.

Approximately one-third of the PM 2.5 improvementobserved in the eastern half of the country can beattributed to reduced sulfates; a large portion of theremaining PM 2.5 improvement is attributable toreductions in carbon-containing particles, especiallyin the Industrial Midwest and the Southeast.

Power plant emissions of sulfur dioxide dropped33% from 1990 to 2003, largely as a result of EPAsAcid Rain program. These reductions yieldedsignificant regional reductions in sulfate concentra-tions, reducing acid deposition and improvingvisibility.

Nationwide, reductions in industrial and highwayvehicle emissions of fine particles and volatileorganic compounds appear to have contributed to

the improvement in PM 2.5 . In the eastern half of the country

regional pollution accounts for more than half of the measured PM 2.5 . This regional pollutioncomes from a variety of sources, including power plants, and can be transported hundreds of miles.

sulfates account for 25% to 55% of PM 2.5 levels.Sulfate levels are similar in urban and nearby ruralareas. Power plants are the largest contributor tothis sulfate formation.

In the Industrial Midwest, Northeast, and southernCalifornia, nitrates make up a large portion of PM 2.5 , especially in winter. Average nitrate concen-trations in urban areas are generally higher thannearby rural levels. Power plants and highwayvehicle emissions are large contributors to nitrateformation.

EPA and states have put in place a number of control programs that will continue to reduceparticle-forming emissions. EPAs 2004 Clean Air Nonroad Diesel Rule will significantly reduce

emissions from nonroad diesel equipment across thecountry. EPAs proposed Clean Air Interstate Rule(proposed December 2003) will reduce PM-forming emissions from power plants in the easternUnited States.


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ComplexPerhaps no other pollutant is as complex asparticle pollution. Also called particulate matter or PM, particle pollution is a mixture of solidparticles and liquid droplets found in the air.Some particles, such as dust, dirt, soot, or smoke,are large or dark enough to be seen with thenaked eye. Others are so small, they can only bedetected using an electron microscope.

These tiny particles come in many sizes and

shapes and can be made up of hundreds of different chemicals. Some particles are emitteddirectly from a source, while others form incomplicated chemical reactions in the atmos-phere. And some can change back and forthfrom gas to particle form. Particle pollution alsovaries by time of year and by location and isaffected by several aspects of weather, such astemperature, humidity, and wind.

Understanding Particle Pollution

Figure 1. Comparison of PM sizes.

Note: In this report, particle size or diameter refers to a normalized measure called aerodynamic diameter, which accounts for the irregular shape and varying density of most particles.

2

Particle Pollution Is

A Continuum of SizesIn general, particle pollution consists of a mixtureof larger materials, called coarse particles, andsmaller particles, called fine particles. Coarseparticles have diameters ranging from about2.5 micrometers (m) to more than 40 m, whilefine particles, also known as known as PM 2.5 ,include particles with diameters equal to or smaller than 2.5 m. EPA also monitors andregulates PM 10 , which refers to particles less thanor equal to 10 m in diameter. PM 10 includes

coarse particles that are inhalable particlesranging in size from 2.5 to 10 m that canpenetrate the upper regions of the bodys respira-tory defense mechanisms. Ultrafine particlesare a subset of PM 2.5, measuring less than 0.1 min diameter.


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Made Up of Many SpeciesParticles are made up of different chemicalcomponents. The major components, or species,are carbon, sulfate and nitrate compounds, andcrustal materials such as soil and ash. Thedifferent components that make up particlepollution come from specific sources and areoften formed in the atmosphere (see Sourcesand Transport of Particle Pollution on page 6).The chemical makeup of particles varies across

SulfatesNitratesCarbonCrustal

Northwest

SouthernCalifornia

Southeast

IndustrialMidwest

Northeast

Southwest

UpperMidwest

Circle size correspondsto PM 2.5 concentration.

WEST EASTFigure 2. Average PM 2.5 composition in urban areas by region, 2003.

Note: In this report, the termsulfates refers to ammonium sulfate and nitrates refers to ammonium nitrate.Carbon refers tototal carbonaceous mass, which is the sum of estimated organic carbon mass and elemental carbon.Crustal is estimated using theIMPROVE equation for fine soil at vista.cira.colostate.edu/improve.

This report summarizes analysis results using the geographic areas shown in this map. The area definitions correspond to the regioused in EPAs 1996 PM Criteria Document (www.epa.gov/ttn/naaqs).

In this report,East includes three regions: the Northeast, the Industrial Midwest, and the Southeast.

the United States (see Figure 2). For example,fine particles in the eastern half of the UnitedStates contain more sulfates than those in theWest, while fine particles in southern Californiacontain more nitrates than other areas of thecountry. Carbon is a substantial component of fine particles everywhere. (For information onthe composition of ultrafine and coarse particlesin Los Angeles, see page 7.)

Health EffectsExposure to particles can lead to a variety of serious healtheffects. The largest particles do not get very far into the lungs,so they tend to cause fewer harmful health effects. Coarseand fine particles pose the greatest problems because theycan get deep into the lungs, and some may even get into thebloodstream. Scientific studies show links between these smallparticles and numerous adverse health effects. Long-termexposures to PM, such as those experienced by people livingfor many years in areas with high particle levels, are associ-ated with problems such as decreased lung function, develop-ment of chronic bronchitis, and premature death. Short-termexposures to particle pollution (hours or days) are associatedwith a range of effects, including decreased lung function,

increased respiratory symptoms, cardiac arrythmias (heartbeat

irregularities), heart attacks, hospital admissions or emergencyroom visits for heart or lung disease, and premature death.Sensitive groups at greatest risk include people with heart orlung disease, older adults, and children.

Environmental EffectsFine particles are the major source of haze that reducesvisibility in many parts of the United States, including ournational parks. PM affects vegetation and ecosystems bysettling on soil and water, upsetting delicate nutrient andchemical balances. PM also causes soiling and erosion damageto structures, including culturally important objects such asmonuments and statues.

Health and Environmental Effects of Particulate Matter



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SeasonalFine particles often have a seasonal pattern. PM 2.5values in the eastern half of the United States aretypically higher in the third calendar quarter (July-September) when sulfates are more readilyformed from sulfur dioxide (SO 2) emissions frompower plants in that region. Fine particle concen-trations tend to be higher in the fourth calendar quarter in many areas of the West, in part becausefine particle nitrates are more readily formed in

cooler weather, and wood stove and fireplace useproduces more carbon.

The time of year also influences daily fine particlepatterns. Unlike daily ozone levels, which areusually elevated in the summer, daily PM 2.5 valuesat some locations can be high at any time of the

year. Figure 4 shows 2003 PM 2.5 levels for Fresno

and Baltimore. The colors in the background of these charts correspond to the colors of the Air Quality Index (AQI), EPAs tool for informingthe public about air pollution levels in their communities. As the Fresno graphic illustrates,fine particles can be elevated in the fall andwinter in some areas, while ozone is elevatedonly in the summer. Contrast the Fresno graphicwith the Baltimore graphic, which shows PM

elevated year-round. Note: Elevated levels onthe AQI do not indicate that an area is violatingEPAs national air quality standards for anyparticular pollutant. The AQI is designed tohelp people reduce their individual exposureto pollution.

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Figure 3. Seasonal averages of PM 2.5 concentration by region, 19992003.



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The AQI is an index for reporting daily airquality. It tells how clean or polluted theair is and what associated health effectsmight be a concern. The AQI focuses onhealth effects people may experiencewithin a few hours or days afterbreathing polluted air. EPA calculates theAQI for five major pollutants regulatedby the Clean Air Act: particulate matter,ozone, carbon monoxide, sulfur dioxide,and nitrogen dioxide. The AQI values forparticulate matter are shown here.

Air Quality Index (AQI) - Particulate Matter

PM2.5 PM10AQI (g/m 3 ) (g/m 3 ) Air Quality Descriptor

050 0.015.4 054 Good

51100 15.540.4 55154 Moderate

101150 40.565.4 155254 Unhealthy for Sensitive Groups

151200 65.5150.4 255354 Unhealthy

201300 150.5250.4 355424 Very unhealthy

Ozone PM 2.5

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Note:These graphs represent data from Federal Reference Method monitors. They do not show data from all monitors that report the Air Quality Index.

Figure 4. Daily PM 2.5 and ozone AQI values, 2003.


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Visibility

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Sources

Particulate matter includes both primary PM, which isdirectly emitted into the air, and secondary PM, which formsindirectly from fuel combustion and other sources. Generally,coarse PM is made up of primary particles, while

fine PM is dominated by secondary particles.Primary PM consists of carbon (soot) emitted from cars,trucks, heavy equipment, forest fires, and burning waste and crustal material from unpaved roads, stone crushing,construction sites, and metallurgical operations.Secondary PM forms in the atmosphere from gases. Some ofthese reactions require sunlight and/or water vapor.Secondary PM includes

Sulfates formed from sulfur dioxide emissions frompower plants and industrial facilities

Nitrates formed from nitrogen oxide emissions from cars,trucks, and power plants

Carbon formed from reactive organic gas emissions fromcars, trucks, industrial facilities, forest fires, and biogenic

sources such as trees.

Cars, trucks, heavy equipment,wild fires, waste burning,and biogenics

Powergeneration

Suspended soiland metallurgicaloperations

Cars, trucks, and

power generation

Carbon

Crustal

SulfatesNitrates

Automobiles, Power Generation, and OtherSources Contribute to Fine Particle Levels

TransportIn the atmosphere, coarse and fine particles behave indifferent ways. Larger coarse particles may settle out from theair more rapidly than fine particles and usually will be foundrelatively close to their emission sources. Fine particles,however, can be transported long distances by wind andweather and can be found in the air thousands of miles fromwhere they were formed.

Sources and Transport of Particle Pollution

Note:Ammonia from sources such as fertilizer and animal feed operations contributes to the formation of sulfates and nitratesthat exist in the atmosphere as ammonium sulfate and ammonium nitrate.

Note: For more information about the apportionment of fine particles to their sources, go to www.epa.gov/oar/ oaqps/pm25/docs.html

One of the most obvious effects of air pollution occurs bothin urban areas and at the countrys best-known and most-treasured national parks and wilderness areas. Visibilityimpairment occurs when fine particles scatter and absorb light,creating a haze that limits the distance we can see and thatdegrades the color, clarity, and contrast of the view. Theparticles that cause haze are the same particles that contributeto serious health problems and environmental damage.Visibility impairmentand the concentration of particles thatcause itgenerally is worse in the eastern United States than itis in the West. Humidity can significantly increase visibilityimpairment by causing some particles to become more efficientat scattering light. Average relative humidity levels are higherin the East (70% to 80%) than in the West (50% to 60%).

In the East, reduced visibility is mainly attributable to sulfates,organic carbon, and nitrates. Poor summertime visibility isprimarily the result of high sulfate concentrations, combinedwith high humidity. Sulfates, which dominate the compositionof these visibility-impairing particles, have been found tocontribute even more to light extinction than they do to fineparticle concentrations. In the West, organic carbon, nitrates,and crustal material make up a larger portion of total particleconcentrations than they do in the East.Through its 1999 regional haze rule, EPA, states, and otherfederal agencies are working to improve visibility in 156national parks and wilderness areas such as the Grand Canyon,Yosemite, the Great Smokies, and Shenandoah. Five multistateregional planning organizations are working together todevelop and implement regional haze reduction plans. Formore information, see www.epa.gov/airtrends/vis.html.

Shenandoah National Park (Virginia) under bad and good visibility conditions.Visual range is 25 km in the left photo and 180 km in the right photo.

Yosemite National Park (California) under bad and good visibility conditions.Visual range is 111 kilometers (km) inthe left photo and greater than 208 km in the right photo.


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After issuing the nations first PM 2.5 standards in 1997, EPAdeveloped the PM Supersites project, a monitoring researchprogram, to address a number of scientific issues associatedwith particulate matter. Program goals focus on obtainingatmospheric measurements to

Characterize PM, its constituents, atmospheric trans-port, and source categories that affect PM in anyregion

Compare and evaluate different PM measurementmethods (e.g., emerging sampling methods, routine

monitoring techniques) Support exposure and health effects research

concerning the relationships between sources, ambientPM concentrations, and human exposures and healtheffects and the biological basis for these relationships.

EPA selected eight locations for Supersites, including LosAngeles. Atmospheric measurements taken at the LosAngeles site between October 2002 and September 2003show that ultrafine particles make up a small portion of thePM concentration compared to inhalable coarse and fineparticles. However, the number of ultrafine particles is signifi-cantly larger than the number of coarse or fine particles. EPAis studying this from a health perspective.The Los Angeles data also show that coarse, fine, and ultra-fine PM have different compositions. For each type of PM,there is a difference in the relative amounts of nitrates,sulfates, crustal materials, and carbon. Carbon, shown hereas organic and elemental carbon, makes up a large fractionof ultrafine and fine PM in Los Angeles.For more information, seewww.epa.gov/ttn/amtic/supersites.html andwww.epa.gov/ttn/amtic/laprog.html

PM Supersites

Los Angeles, CA(University of Southern California Site)

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Both Local and RegionalBoth local and regional sources contribute toparticle pollution. Figure 5 shows how much of the PM 2.5 mass can be attributed to local versusregional sources for 13 selected urban areas(arranged west to east). In each of these urbanareas, monitoring sites were paired with nearbyrural sites. When the average rural concentrationis subtracted from the measured urban concen-tration, the estimated local and regional contri-butions become apparent.

In the East, regional pollution contributes morethan half of total PM 2.5 concentrations. Ruralbackground PM 2.5 concentrations are high in theEast and are somewhat uniform over largegeographic areas. These regional concentrationscome from emission sources such as power plants, natural sources, and urban pollution andcan be transported hundreds of miles.

Measured PM 2.5 Concentration

Missoula

Salt Lake City

Tulsa

St. Louis

Birmingham

Indianapolis

Atlanta

Cleveland

Charlotte

Richmond

Baltimore

New York City

0 5 10 15 20 25 30Annual Average PM 2.5 Concentration, g/m 3

Fresno

WESTEAST

RegionalContributionLocalContribution

Figure 5. Local and regional contribution to urban PM 2.5 .

For the cities shown in Figure 5, local contribu-tions range from 2 to 20 micrograms per cubicmeter (g/m 3 ), with the West generally showinglarger local contributions than the East. In theEast, local contributions are generally greatest incities with the highest annual average PM 2.5concentrations.

Figure 6 shows the local and regional contri-butions for the major chemical components thatmake up urban PM 2.5: sulfates, carbon, and

nitrates. In the eastern United States, the localcontribution of sulfates is generally small. Mostsulfates in the East are converted from regionalSO 2 emissions and are transported long distancesfrom their sources.

Carbon has the largest local contribution of thethree major chemical components. These localemissions come from a combination of mobileand stationary combustion sources. The regional

Note: Urban and nearby rural PM 2.5

concentrations suggest substantial regional contributions to fine particlesin the East.The measured PM 2.5 concentration is not necessarily the maximum for each urban area.


Regional concentrations are derived from the rural IMPROVE monitoring network,http://vista.cira.colostate.edu/improve.


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Figure 6. Local and regional contribution of major PM 2.5 chemical components.

contribution, which varies from 30% to 60% of the total carbon at urban locations, is from rural

emission sources such as vegetation and wildfires,as well as region-wide sources such as cars andtrucks.

Missoula

Salt Lake City

Tulsa

St. Louis

Birmingham

Indianapolis

Atlanta

Cleveland

Charlotte

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Baltimore

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Sulfates

Annual Average Concentrationof Sulfates, g/m 3

Carbon

Missoula

Salt Lake City

Tulsa

St. Louis

Birmingham

Indianapolis

Atlanta

Cleveland

Charlotte

Richmond

Baltimore

New York City0 6 10 12

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42 8Annual Average Concentration

of Carbon, g/m 3

Missoula

Salt Lake City

Tulsa

St. Louis

Birmingham

Indianapolis

Atlanta

Cleveland

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Nitrates

Annual Average Concentrationof Nitrates, g/m 3

Nitrates represent only about 10% to 30% of annual average PM 2.5, and urban concentrations

are higher than the nearby regional levels. This islikely due to local nitrogen sources such as cars,trucks, and small stationary combustion sources.

Note: Regional concentrations are derived from the rural IMPROVE monitoring network,http://vista.cira.colostate.edu/improve.


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1010.1 - 1515.1 - 20> 20

PM2.5 , 2003

Concentration range ( g/m 3)

10

concentrations greater than the PM 10 or PM 2.5national air quality standards. Thir ty-seven

counties (21 million people) measured concen-trations in excess of the national PM 10 standards,and 72 counties (53 million people) exceeded thenational PM 2.5 standards. These numbers do notinclude other areas outside of these counties thatmight contribute to levels above the standards.

Figure 7 shows the range of PM 10 concentrationsacross the country in 2003. The highest concen-trations were recorded in Inyo and Mono coun-ties, California; El Paso County, Texas; and DonaAna County, New Mexico. Figure 8 shows the

Nationally, fine particle concentrations in 2003were the lowest since nationwide PM 2.5 moni-

toring began in 1999. Compared with 2002, thebiggest decreases occurred in the IndustrialMidwest and parts of California areas withrelatively high PM 2.5 concentrations. PM 10 concen-trations were slightly higher in 2003 than theprevious year, but they are still the second lowestsince nationwide PM 10 monitoring began in 1988.

Although average concentrations have declinednationally, many areas still exceed the level of the PM standards. In 2003, monitors in 97counties (home to 62 million people) showed

Particle Pollution in 2003


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55 - 154155 - 354> 354

Figure 8. PM 2.5 concentrations, 2003 (annual average).

Figure 7. PM 10 concentrations, 2003 (second maximum 24-hour).

Note: Circle size correspondsto PM 2.5 concentration range.


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range of 2003 PM 2.5 annual averages across thecountry. The highest annual averages occurredin southern California and Pittsburgh. Highlevels are also seen in many urban areas in the

Southeast, Northeast, and Industrial Midwest. Seewww.epa.gov/airtrends/pm.html for county-levelmaps of PM.

PM 2.5 concentrations can reach unhealthy levelseven in areas that meet the annual standard. In2003, there were 277 counties with at least

1 unhealthy day based on PM 2.5 AQI values, asshown in Figure 9. Nearly two-thirds of thosecounties had annual averages below the level of the standard. Figure 10 shows how several major

metropolitan areas fared in 2003 relative toprevious years. Most metropolitan areas had fewer unhealthy PM 2.5 days in 2003 compared to theaverage from the previous 3 years, which reflectsthe improvements observed in 2003.

Number of AQIDays Above 100

None1 - 56 - 1011 - 30> 30

Figure 9. PM 2.5 AQI days above 100 ( 40.5 g/m 3) in 2003.

New York

Washington, DCCincinnati

Chicago

St. Louis

BirminghamAtlanta

Minneapolis

Charlotte

Dallas

Fresno

SacramentoSalt Lake City

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Figure 10. Number of days with PM 2.5 AQI levels above 100, 2003 versus average 20002002.

Note:This map represents data from Federal Reference Method monitors. It does not show data from all monitors that report the Air Quality Index.As such, it may not provide a complete picture of days above the AQI in some cities.


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EPA first established National Ambient Air Quality Standards(NAAQS) for total suspended particulate (TSP) in 1971.When the standards were revised in 1987, TSP was replacedby PM 10 . In 1997, EPA revised the primary (health) andsecondary (welfare) PM NAAQS by adding standards forPM2.5 . EPA added PM 2.5 standards because fine particlesare more closely associated with serious health effects.The NAAQS for PM 10 and PM 2.5 include both short-term(24-hour) and long-term (annual) standards:

NAAQS PM 2.5 PM10

Short-term 65 g/m 3 150 g/m 3

(24-hour average)

Long-term 15 g/m 3 50 g/m 3

(annual average)

12

PM 10 PM 2.5

Particulate matter varies greatly in size. Coarseparticles can be as large as 40 micrometers (m)in diameter or even larger. EPA's NationalAmbient Air Quality Standards (NAAQS) for particulate matter, however, have focused onparticles that are 10 m in diameter or smaller.These particles are the most likely to be inhaledand can penetrate into the lower respiratory tract.EPA has had air quality standards for particles10 m and smaller since 1987. In 1997, EPA alsoestablished an NAAQS for fine particles thoseparticles 2.5 m in diameter or smaller. EPA isnow in the process of reviewing the PMNAAQS.

As shown in Figure 11, the size distribution of particles smaller than 10 m but larger than2.5 m varies by geographic location. Levels of PM 10-2.5 are generally higher in the West, particu-larly the Southwest. PM 10-2.5 typically comprisesmore than half of the PM 10 mass in the West.Data also suggest that concentrations of particlesbetween 2.5 and 10 m in size are lower in themid-Atlantic and Southeast. Overall, whiledirectly emitted PM 2.5 and its precursors cancome from both local and regional sources, thelarger particles that are part of PM 10 tend tocome from local sources.

Figure 11. Percent of 2003 annual average concentration of particles smallerthan 10 m but larger than 2.5 m, by region.

National Standards for Particulate Matter

ComplianceEach PM standard carries a separate threshold forcompliance:

For the long-term standards for both PM 2.5 and PM 10 ,compliance is determined based on the average of three

consecutive annual average values. Compliance with the short-term PM 2.5 standard is

determined by the 3-year average of the annual 98thpercentile of 24-hour concentrations.

The short-term standard for PM 10 is not to be exceededmore than once per year, averaged over 3 years.

EPA reviews the NAAQS on a regular basis. The standardsfor PM 10 and PM 2.5 are currently under review, to becompleted in 2006.

North-west

SouthernCA

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PM2.5PM10-2.5

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0%

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Note: g/m 3 = micrograms per cubic meter.


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PM 10 National and Regional TrendsNationally, PM 10 concentrations have decreased

31% since 1988, as shown in Figure 12.Regionally, PM 10 decreased most in areas withhistorically higher concentrations theNorthwest (39%), the Southwest (33%), andsouthern California (35%).

Programs aimed at reducing direct emissions of particles have played an important role inreducing PM 10 concentrations, particularly in

western areas. Some examples of PM 10 controlsinclude paving unpaved roads, replacing woodand coal with cleaner-burning fuels like naturalgas, and using best management practices for agricultural sources of resuspended soil.Additionally, EPAs Acid Rain Program hassubstantially reduced SO 2 emissions from power plants since 1995 in the eastern United States,contributing to lower PM concentrations. Directemissions of PM 10 have decreased approximately25% nationally since 1988.

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In 1996, EPA refined itsmethods for estimatingemissions.

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National Standard: 50 g/m 3

Regional Trend

39%

35.521.5

29%

34.224.3

29%

28.820.5

25%

32.924.633%

39.526.535%

42.3 27.6

UpperMidwest

16%

35.8 29.9

Annual Average PM 10 Concentrations, 19882003

National PM 10 Air Quality

National Direct PM 10 Emissions

Looking at Trends

Figure 12. Regional and national trends in annual average PM 10 concentrations and emissions,

19882003.


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PM 2.5 National and Regional TrendsPM 2.5 concentrations have decreased 10% nation-ally since 1999. Generally, PM 2.5 has decreasedthe most in regions with the highest concentra-tions the Southeast (20%), southern California(16%), and the Industrial Midwest (9%), as shownin Figure 13. With the exception of theNortheast, the remaining regions posted modestdeclines in PM 2.5 from 1999 to 2003.

A variety of local and national programs haveresulted in a 5% decrease in estimated directemissions of PM 2.5 over the past 5 years. In addi-

tion, programs that reduce the gaseous emissionsthat can form particles in the atmosphere have yielded additional reductions. National programs

that affect regional emissions includingEPAs Acid Rain Program have contributed

to lower sulfate concentrations and, conse-quently, to lower PM 2.5 concentrations, partic-ularly in the Industrial Midwest and Southeast.National ozone-reduction programs designedto reduce emissions of volatile organiccompounds (VOCs) and nitrogen oxides(NO x ) also have helped reduce carbon andnitrates, both of which are components of PM 2.5 . Nationally, SO 2 , NO x , and VOC emis-sions decreased 9%, 9%, and 12%, respectively,from 1999 to 2003. In eastern states affected

by the Acid Rain Program, sulfates decreased7% over the same period.


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Northwest

SouthernCalifornia

UpperMidwest

Southeast

IndustrialMidwest

Northeast

Southwest

National Standard: 15 g/m 3

Regional Trend

9.010.5

15% 10.711.46% 14.115.6

9%

13.413.2

1%

12.615.7

20%

16.920.0

16%8.18.7

7%

Figure 13. Regional and national trends in annual average PM 2.5 concentrations and emissionsrelated to PM 2.5 formation, 19992003.

Annual Average PM 2.5 Concentrations, 19992003

99 00 01 02 03

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Air Quality

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PM2.5

Fuel Combust ion Indust rial Processes Transpor ta tion

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NOxSO230

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Only a subset of VOC contributes to PM 2.5

Note: Ammonia is a contributor to PM 2.5 formation. However, because of uncertainty in ammoniaemission estimates, its trends are not shown here.


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years, average PM 2.5 levels in 2003 were thelowest on record. Low-sulfur gasoline use

and ozone reduction programs designed tocontrol NO x and VOC emissions may havecontributed to the PM 2.5 decrease observedin the 1990s.

Washington, DC: PM 2.5 concentrations arecurrently (2003) at their lowest levels. Therelatively large drop from 1994 to 1995corresponds to decreases in sulfates (21%) andorganic carbon (30%). The decrease insulfates is attributable in part to the AcidRain Program, which substantially reduced

SO 2 emissions from power plants during thistime. The decrease in organic carbon isattributable in part to the use of reformulatedgasoline.

Chicago: PM 2.5 concentrations at this sitehave dropped substantially since the early1980s, reaching their lowest levels in 2003.

For additional information on long-term trends,see www.epa.gov/airtrends/pm.html.

25-Year PM 2.5 TrendsBecause EPAs national PM 2.5 monitoringnetwork is just 5 years old, we use data from

older PM 2.5 monitoring networks to assesslonger-term trends. Although the earlier networks are more limited in geographic scopeand years of coverage, their data do providehistorical perspective. The maps in Figure 14show how PM 2.5 concentrations 25 years agocompare with PM 2.5 concentrations today in39 major cities. Reductions vary among the 39cities. Generally, the largest reductions occurredin the areas with the highest concentrations. Onaverage, todays levels are about 30% lower thanthey were 25 years ago.

The following examples, illustrated in Figure 14,show how PM 2.5 concentrations have improvedover the past 25 years in three cities. Figure 14also shows PM 10 concentrations for comparison(where available). PM 2.5 accounts for more thanhalf of the PM 10 levels in these areas.

Los Angeles: PM 2.5 concentrations havedecreased substantially since 1980. Althoughconcentrations have leveled off in recent


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Figure 14. Comparison of historical PM 2.5 and PM 10 annual average concentrations, 19792003.


15 [5 Cities]15.1 - 20 [13 Cities]20.1 - 25 [14 Cities]25.1 - 30 [5 Cities]> 30 [2 Cities]

Average Annual PM 2.5 Concentrations, 19791983

Source: Inhalable Particulate Network


15 [24 Cities]15.1 - 20 [13 Cities]

> 20 [2 Cities]

Average Annual PM 2.5 Concentrations, 20012003

Source: Federal Reference Method Network

Note: The 19791983 data are from the Inhalable Particulate Network (IPN).The 19841999 data are from EPAs Air Quality System.The 19992003 data are from the Federal Reference Method (FRM) network.The 19932003 data for Washington, DC, are from the IMPROVE network.

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Episodic Events

Rural Sulfate TrendsIn the eastern half of the United States, sulfatesaccount for 25% to 55% of PM 2.5 annually. Power plants are the largest contributor to sulfate formationin the East, where they were responsible for more than75% of sulfur dioxide emissions in 2003.

In the East, power plants reduced sulfur dioxide emis-sions 33% between 1990 and 2003. As Figure 15shows, this downward trend matches well with thetrend in concentrations of rural sulfates (a 29%decrease). Because sulfates have such a large regionalcomponent (shown in Figure 6), these trends in sulfateconcentration can also be used to help explain urbanPM 2.5 trends.

The reductions shown in Figure 15 are primarilyattributable to implementation of EPAs Acid Rainprogram. Phase I compliance began in 1995, affectinglarge coal-burning power plants in 21 eastern andmidwestern states. Phase II implementation began in2000, tightening emission limits on the Phase I power plants and setting restrictions on smaller coal-, oil-, andgas-fired plants. As the figure shows, sulfur dioxideemissions and sulfate concentrations decreasedfollowing implementation of both phases. A slightincrease in SO 2 emissions in the latter half of the 1990swas likely due to power plants not affected until Phase

II began in 2000. The small increase from 2002 to 2003resulted from increased electricity production by coal-fired and oil-fired units. These units emit much moreSO 2 than natural gas units that generated less power in2003. This annual variation does not affect the totallimit on SO 2 emissions under the Acid Rain Program.(For more information, see www.epa.gov/air/oap.htmland www.epa.gov/acidrainreport/.)

15,000

10,000

5,000

090 91 92 93 94 95 96 97 98 99 00 01 0302

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Sulfate ConcentrationsSO2 Emissions from Power Plants

Figure 15. Eastern annual trends of sulfur dioxideemissions from power plants and sulfate concentrations. Satellite photo of forest fires, southern

California, October 27, 2003.

PM concentrations can increase dramatically due tohuman-caused or natural episodic events, such as biomassburning, meteorological inversions, dust storms, andvolcanic and seismic activity. These events are rare,affecting less than 1% of reported PM 2.5 concentrationsbetween 2001 and 2003. Episodic events can affectpeoples short-term PM exposure, briefly pushing hourlyand daily PM levels into the unhealthy ranges of the AirQuality Index. However, these events rarely have a signifi-cant effect on annual or longer averages of PM.Biomass burning can be either a human-initiated event, asin the burning of vegetation for land clearing or land usechange, or a natural event, as in the wild fires resultingfrom lightning. Biomass burning can significantly increasePM levels in local areas and sometimes more distant areas.Air currents can carry smoke from forest fires half-way

around the earth. Organic carbon compounds usuallydominate the PM 2.5 concentration profile during thesefire episodes.Topography and meteorological conditions make someareas more susceptible to episodic events. In mountainregions, temperature inversions sometimes trap pollutedair during the winter. Wintertime PM 2.5 and PM 10 canbe more than three times higher than other seasonalaverages. Woodstove smoke, containing large amounts

Note: Sulfate concentrations are from EPAs CASTNET monitoring network, www.epa.gov/castnet


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Dust storm, Phoenix, Arizona, August 19, 1999.

Temperature inversion, Salt Lake Valley, Utah,January 13, 2004.

of organic carbon, is often identified as a significant sourceof the elevated wintertime PM concentrations.Arid desert conditions in the southwestern United Statesmake this region more vulnerable to wind-blown dust thanother regions of the nation. Most dust events are causedby passage of weather fronts and troughs and downmixingof upper-level winds. Cyclone development and thunder-storms result in the most dramatic dust clouds with thelowest visibilities. Dust-related events are typically domi-nated by large, coarse particles, but fine particle levels alsoincrease.The effects of dust storms can also be seen globally. Giantsand storms originating in the Sahara Desert can blowacross the Atlantic to South America, the Caribbean, andthe southeastern United States, transporting severalhundred million tons of dust each year. Movement of dust

from Africa has increased since 1970 because of an increaseof dry weather in the Saharan region. Satellite picturesalso confirm that sandstorms originating in Chinas GobiDesert occasionally cross the Pacific to the United States.Transport from Africa typically occurs in the summer, andtransport from Asia typically occurs in the spring.

Satellite photo of giant cloud of dust originatingin North Africa moving westward.


24/3220

Note: Sulfate and nitrate concentrations from the CASTNET monitoring network were adjusted to represent mass inPM 2.5 and include ammonium as well as water.Trends for crustal were not available so constant values based on20022003 data for each region were used. See www.epa.gov/airtrends/pm.html for further details.

concentrations in the eastern United States matchwell with trends in SO 2 emissions from power plants over the past 14 years (based on analyses

discussed in the previous section; see Figure 15).Figure 17 shows that, on smaller subregionalscales, the relationship between sulfate concentra-tions and power plant SO 2 emissions can varyamong the subregions. Although trends in sulfateconcentrations and SO 2 emissions match bestoverall in the Southeast (SO 2 emissions down15%, sulfate concentrations down 13%, from1999 to 2003), the year-to-year comparisons for the Industrial Midwest and the Northeast do notshow such a close match. Sulfur dioxide emis-

sions in the Industrial Midwest declined 19%,while sulfate concentrations declined 5%. In theNortheast, sulfur dioxide emissions were down6%, and sulfate concentrations were up 3%.

These subregional differences may be caused byseveral factors, the most important of which islikely to be transport. As Figure 17 shows, theratio of sulfate concentrations to SO 2 emissions ishigher in the Northeast than in the other regions. This suggests that transport of emissions

PM 2.5 Trends in Three Regions(19992003)

To better understand ambient air quality, it ishelpful to examine trends and the factors thatcontribute to those trends in specific regions. Thissection explores, in detail, trends in three regions inthe eastern half of the country from 1999 to 2003.

Figure 16 shows the 5-year regional trends inurban PM 2.5 and its major chemical constituents.In the Southeast, PM 2.5 declined sharply from1999 to 2002, with little further change to 2003.Overall, the Southeast shows a 20% decrease inPM 2.5 from 1999 to 2003. In the IndustrialMidwest, there is a gradual downward PM 2.5trend from 1999 to 2001 and a more pronounceddecrease from 2001 to 2003. Overall, PM 2.5decreased 9% over the 5-year period. In theNortheast, PM 2.5 increased slightly from 1999through 2001, then decreased through 2003,for an overall increase of 1%. Trends in PMcomponents indicate that reductions in sulfatesappear to be responsible for approximately one-third of the reductions in PM 2.5 in the IndustrialMidwest and the Southeast. Trends in sulfate

Explaining the Trends

Figure 16. Trends in PM 2.5 and its chemical constituents, 19992003.

Industrial Midwest

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Year1999 2000 2001 2002 2003

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119 PM 2.5 Monitoring Sites

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+1%

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Effect of MeteorologyWeather plays a role both in the atmospheric

formation of PM 2.5 and in the quantity of emis-sions that contribute to this pollution. For thisreport, we examined the effect of meteorologyon sulfates, which are a major component of PM 2.5 , especially in the eastern half of the UnitedStates. To assess the effect of meteorology onannual average sulfate concentrations, EPA hasconducted a preliminary analysis, adjusting sulfatelevels based on weather conditions. (The blueline in Figure 17 represents measured sulfateconcentrations; the red line represents the meteo-rologically adjusted sulfate concentrations.) Oneof the main parameters driving these preliminaryadjustments is temperature. In the eastern half of the United States, 1999, 2001, and 2003 werenear-normal meteorological years, so onlyminimal adjustments to sulfate concentrationswere needed. In 2000, however, a cool summer may well have caused sulfur dioxide emissions tobe lower than average, resulting in lower amountsof sulfates in the air. Adjusting for weather in2000 raised estimated sulfate levels in all threeregions to the level expected during a year with

average weather conditions.

Conversely, the summer of 2002 in the easternUnited States was one of the hottest in recent

years. Sulfur dioxide emissions were higher that year, likely due (at least in part) to increaseddemand for electricity for cooling. The meteoro-logical adjustment for 2002 reduces the amountof sulfates in all three regions to levels expectedduring a normal meteorological year.

In two of the three regions, the variations in

power plant SO 2 emissions (illustrated by the yellow bars in Figure 17) generally correlate moreclosely with the meteorologically adjusted sulfates(the red line) than the unadjusted sulfates (theblue line). In the Industrial Midwest, however,adjusting for weather causes the sulfate trend tomove farther away from the sulfur dioxide emis-sion trend in 2002-2003. More refined meteoro-logical analyses and emission inventories arenecessary to fully understand these results.

90 91 92 93 94 95 96 97 98 99 00 01 02 030

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SO2 emissions from power plants CASTNET sulfate concentrationsMeteorologically adjusted sulfate concentrations

Year

Figure 17. Meteorologically adjusted sulfateconcentrations, 19992003.

from other regions contributes to sulfate forma-tion in the Northeast. Other factors that maycontribute to the subregional differences in thesetrends include variations in meteorological condi-tions that are important to sulfate formation andtransport, contributions to the Northeast fromCanada, and subregional differences in the contri-butions of sources other than power plants.


26/3222

The PM 2.5 RemainderFigure 16 (page 20) also shows the estimatedtrend in the PM 2.5 remainder for each of thethree regions. The remainder is estimated bysubtracting all known PM 2.5 components fromthe total PM 2.5 mass. Some uncertainties exist inour interpretations of these data; however, thePM 2.5 remainder appears to consist mostly of carbon-containing particles. Some small contri-butions to the PM 2.5 remainder trend shown inFigure 16 include

Trends in crustal material Local contributions for nitrates and sulfates

(see the discussion on pages 8 and 9) Any changes in data quality or the operation

of EPAs PM 2.5 Federal Reference Methodmonitoring network during its first few yearsof operation.

Despite the uncertainties, the reductions in thePM 2.5 remainder for the Industrial Midwest andSoutheast appear to be due, in large part, toreductions in emissions that contribute to theformation of carbon-containing particles. Therelative importance of various man-made emis-sions sources to these trends is uncertain and mayvary by region and urban area. Important sourcesof carbon-containing particles in urban air include direct emissions from sources such asmotor vehicles, fuel combustion, and fires andatmospheric transformation of certain organicgases, including both regional biogenic emissionsand some components of man-made VOCs.

It is interesting to note that, in Figure 18, thedecrease in the estimated PM 2.5 remainder corre-sponds either to reductions in directly emittedfine particles or reductions in man-made VOCemissions. The Northeast region, however, showsvirtually no net change in PM 2.5 or in any of itsestimated components. Yet both direct PM 2.5emissions and VOC emissions decreased from1999 to 2003. EPA is continuing to conductresearch and analysis to better identify andquantify key direct emission sources in additionto the relative contribution of man-made VOCemissions to atmospheric formation of carbon-containing particles.

Figure 18. PM 2.5 emission trends.

96 97 98 99 00 01 02 030

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will be required to attain the National AmbientAir Quality Standards for fine particles. EPAs

proposed Clean Air Interstate Rule (proposedin December 2003) will help states meet thoserequirements by reducing SO 2 and NO x emis-sions in the eastern United States thus reducingparticle pollution transported across state bound-aries. Another regulation, the Best AvailableRetrofit Technology (BART) program, willrequire the older, existing power plants to controlPM emissions with retrofit pollution controlequipment. Also, national mobile source rules arein place to strengthen the emission requirements

for virtually all types of mobile sources. Manylocalities also have pollution reduction require-ments for diesel engine retrofits as well as sulfur limits in diesel and gasoline engines.

For more details on the PM 2.5 remainder, seeww.epa.gov/airtrends/pm.html. For information

on EPAs monitoring networks, seewww.epa.gov/ttn/amtic/.

Control ProgramsMany programs have been put in place to reducelevels of particulate matter. Table 1 lists the major emission control programs that have contributedto reductions in PM since 1995 and willcontinue to reduce PM in the future. Theseprograms control direct PM emissions and/or theemissions that contribute to PM formation, such

as SO 2 , NO x , and VOCs. The control programsconsist of a series of regulations that reduce emis-sions from many stationary and mobile sourcesectors. For example, beginning in 2008, states

PM PrecursorsDirect PM a SO2 NOx VOC Implementation

Program Sector Reductions Reductions Reductions Reductions Date

Clean Air Nonroad Mobile sources X X X 2004-2015

Diesel RuleClean Air Interstate Rule Electric Utilities X X X 2010-2015(proposed December 2003)Acid Rain Program Electric Utilities X X 1995-2010

NOx SIP Call Electric Utilities X X 2004

Regional Haze Rule/ Electric Utilities b X X X 2013-2015Best Available RetrofitTechnology

PM2.5 Implementation c Stationary/Area/ X X X X 2008-2015Mobile sources

PM10 SIPs Stationary/Area/ X X X X Ongoing(e.g., San Joaquin Valley) Mobile sourcesMaximum Achievable Stationary/Area X X 1996-2003Control Technology

(MACT) Standardsd

Various Mobile X X X X OngoingSource Programs e

a Includes elemental and organic carbon, metals, and other direct emissions of PM.b Also applies to industrial boiler and the other source categories also covered under Prevention of Significant Deterioration (PSD).c Includes Reasonably Available Control Technology (RACT) and Reasonably Available Control Measures (RACM).d Includes a variety of source categories such as Boilers and Process heaters, Pulp and Paper, Petroleum Refineries, various minerals and ores,

and others. While these standards are for hazardous air pollutants (HAPs) such as metals, measures to reduce HAPs in many cases alsoreduce PM emissions.

e Includes such programs as onroad diesel and gasoline engines, nonroad gasoline engines, Low Sulfur Diesel and Gasoline Fuel Limits foronroad and offroad engines, Motorcycles, Land-based recreational vehicles, and Marine diesel engines.

Table 1. A Selection of Emission Control Programs Contributing to PM Emission Reductions, 19952015


28/3224

The most direct way to obtain surface concentration datafor particles is from the routine measurements made at surfacemonitoring stations across the United States. This approach has

some limitations, however, because large regions of the countrydo not have surface monitors, and coastal regions are often influ-enced by polluted air approaching over water. In addition, pollu-tion may be transported aloft, undetected by surface monitors,and then descend to influence air at the ground. New workbeing done through a collaborative partnership between EPA,the National Aeronautics and Space Administration (NASA), andthe National Oceanic and Atmospheric Administration (NOAA)uses satellite observations to augment the surface networkmonitoring data with satellite data.The NASA MODIS (Moderate Resolution Imaging Spectro-radiometer) instruments on board the EOS (Earth ObservingSystem) satellites EOS-Terra and EOS-Aqua provide twice-dailymeasurements of aerosol optical depth (AOD), a measure of howmuch light airborne particles prevent from passing through acolumn of atmosphere. Scientists use these measurements toestimate the relative amount of aerosols suspended in theatmosphere.

Initial research shows that MODIS-derived data are suitable fortracking air quality events on a regional scale and may be a goodsurrogate for estimating the intensity of surface PM 2.5 concentra-tions. More research and data are needed to help show howaerosol loads are distributed vertically in the atmosphere so thatMODIS-derived AOD can be put into the proper context. Formore information on the MODIS-derived AOD and PM 2.5 pollu-tion events, go to the Cooperative Institute for MeteorologicalSatellite Studies/Space Science and Engineering Center at theUniversity of Wisconsin-Madison website: http://idea.ssec.wisc.edu.

Composites of MODIS-derived AOD (color) and cloud optical thickness (black-white) from September 5 to 8, 2003. Themajority of the high AOD seen in the images (yellow-red) was the result of several very large wildfires in western NorthAmerica from British Columbia to Oregon. MODIS-derived AOD tracked the movement of the plume, which eventuallyaffected surface PM 2.5 concentrations throughout the midwestern United States.

IDEA (Infusing satellite Data into EnvironmentalApplications) is a partnership between EPA, NASA, and

NOAA. These agencies are working to improve airquality assessment, management, and prediction byinfusing satellite measurements from NASA into EPAand NOAA analyses for public benefit.

1 2

3 4

Using Satellites to Track Particulate Matter


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National and regional regulations will makemajor reductions in ambient PM 2.5 levels over thenext 10 to 20 years. In particular, the proposed

Clean Air Interstate Rule (CAIR) and theexisting NO x SIP Call, will reduce SO 2 and NO xemissions from certain electric generating unitsand industrial boilers across the eastern half of theUnited States. Regulations to implement theambient air quality standards for PM 2.5 willrequire direct PM 2.5 and PM 2.5 precursor controlsin nonattainment areas. New national mobilesource regulations affecting heavy-duty dieselengines, highway vehicles, and other mobilesources will reduce emissions of NO x , direct

PM 2.5 , SO 2 , and VOCs.EPA estimates that current and proposed regula-tions for stationary and mobile sources will cutSO 2 emissions by 6 million tons annually in 2015from 2001 levels. NO x emissions will be cut9 million tons annually in 2015 from 2001 levels.VOC emissions will drop by 3 million tons, anddirect PM 2.5 emissions will be cut by 200,000tons in 2015, compared to 2001 levels. Figure 19shows anticipated emission reductions. Most of the SO 2 reductions are associated with electric

generating sources, while NO x and VOC reduc-tions for mobile sources are associated withcontinuing improvements in onroad and nonroadvehicles.

Models predicting the effect of these emissionreductions on air quality show that all areas inthe eastern United States will have lower PM 2.5concentrations in 2015 relative to present-dayconditions. In most cases, the predicted improve-ment in PM 2.5 ranges from 10% to 20%. EPAestimates that the proposed CAIR combinedwith existing regulations will bring the majorityof the counties in the East into attainment for thePM 2.5 standards. As Figure 20 shows, 99 easterncounties are estimated to have exceeded theannual PM 2.5 standard in the 19992002 period,but only 13 of those counties are projected toexceed the PM 2.5 standard by 2015. More infor-mation on CAIR can be found at:www.epa.gov/interstateairquality/.

0

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T o n s

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Figure 19. Projected emission reductions by 2015.

Figure 20. Estimated reduction in number of coun-ties exceeding PM 2.5 standards from 2001 (99) to

2015 (13), based on current programs plus the CleanAir Interstate Rule as proposed in December 2003.

Ambient PM 2.5 , 1999200299 Counties Exceeding PM 2.5 Standards

Estimated PM 2.5 , 201513 Counties Exceeding PM 2.5 Standards

The Future


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Upcoming PM 2.5 DesignationsEPA designates areas as attaining or not attainingthe National Ambient Air Quality Standards for fine particulate matter (PM 2.5 ). EPA designates anarea as nonattainment if it has violated the annual

or 24-hour national PM 2.5 standard (assessed over a 3-year period) or if it has contributed to a viola-tion of one of the standards. Once designated,nonattainment areas must take actions to improvetheir PM 2.5 air quality on a certain timeline.Designations are a crucial first step in the effortsof states, tribes, and local governments to reduceharmful levels of fine particles. For more details onPM 2.5 designations, visit www.epa.gov/pmdesignations.

Note: Designations are based on 3 years of data,and the boundaries of defined nonattainment areasmay differ from the county boundaries used inthis report.

PM 2.5 and Other PollutantsAreas that experience PM 2.5 concentrations thatexceed the National Ambient Air QualityStandards can also have air quality problems associ-ated with other pollutants. This association in the

presence of different pollutants is not unexpected.A 2004 report by the National Academies of Sciences (Air Quality Management in the United States) indicates that air pollutants often sharesimilar precursors and similar chemical reactionsonce in the atmosphere. For example, nitrogenoxides, which contribute to PM 2.5 formation, arealso a key ingredient in ground-level ozone.

Pollutants may also be emitted from the same typesof sources. Industries that emit air toxics may alsoemit chemicals that contribute to ozone or PM

formation. Data indicate that millions of peoplelikely live in areas where particle pollution levelsare elevated along with ozone and/or air toxics.EPA will continue to analyze this information aswe work to protect public health across thecountry.


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For Further InformationWeb Sites

Additional technical information: www. epa.gov/airtrends/pm.htmlAir Quality Index (AQI): www.epa.gov/airnow

Clean Air Interstate Rule: www.epa.gov/interstateairquality/CASTNET: www.epa.gov/castnet/Emissions: www.epa.gov/ttn/chief/EPA 1996 PM Criteria Document: www.epa.gov/ttn/naaqsEPA Monitoring Networks: www.epa.gov/ttn/amtic/Health and Ecological Effects: www.epa.gov/air/urbanair/pm/index.htmlIMPROVE: vista.cira.colostate.edu/improveNational Academies: www4.nationalacademies.org/nas/nashome.nsf Office of Air and Radiation: www.epa.gov/oar Office of Air Quality Planning and Standards: www.epa.gov/oar/oaqps

Office of Atmospheric Programs: www.epa.gov/air/oap.htmlOffice of Transportation and Air Quality: www.epa.gov/otaqOnline Air Quality Data: www.epa.gov/air/data/index.htmlPM Supersites: www.epa.gov/ttn/amtic/supersites.html and www.epa.gov/ttn/amtic/laprog.htmlPM 2.5 Designations: www.epa.gov/pmdesignationsReport on Acid Rain: www.epa.gov/acidrainreport/Satellite information: idea.ssec.wisc.eduSource apportionment: www.epa.gov/oar/oaqps/pm25/docs.htmlVisibility: www.epa.gov/airtrends/vis.html

AOD aerosol optical depthAQI Air Quality IndexBART best available retrofit technologyCAA Clean Air ActCAIR Clean Air Interstate RuleCASTNET Clean Air Status and Trends

NetworkEOS Earth Observing SystemEPA U.S. Environmental Protection

AgencyFRM Federal Reference MethodHAP hazardous air pollutantsIDEA Infusing satellite Data into

Environmental ApplicationsIMPROVE Interagency Monitoring of

Protected Visual EnvironmentsIPN Inhalable Particulate Networkkm kilometer

MACT maximum achievable controltechnologyMODIS moderate resolution imaging

spectroradiometer NAAQS National Ambient Air Quality

Standards

NASA National Aeronautics and SpaceAdministration

NOAA National Oceanic and AtmosphericAdministration

NO x oxides of nitrogenPM particulate matter

PM 10 particulate matter 10 m or less insize

PM 2.5 particulate matter (fine) 2.5 m or less in size

PM 102.5 particulate matter (coarse) between10 and 2.5 m in size

PSD prevention of significantdeterioation

RACM reasonably available controlmeasures

RACT reasonably available controltechnology

SIP State Implementation PlanSO 2 sulfur dioxideTCM total carbonaceous massTSP total suspended particulateg/m 3 micrograms per cubic meter m micrometersVOC volatile organic compound

Acronyms


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Documents