particle pollution

7/29/2019 Particle Pollution

1/102 0 O u r N a t i o n s A i r

Particle pollution refers to two classes of particlesne and coarse. Tese classes are based in part onlong-established information about dierences insources, properties, and atmospheric behavior. EPA hasset national standards to protect against the health and

welfare eects associated with exposures to ne andcoarse particles. Fine particles are generally consideredto be less than or equal to 2.5 micrometers (m) inaerodynamic diameter, or PM

2.5. Coarse particles

are those between 2.5 and 10 m in diameter. PM10

(particles generally less than or equal to 10 m indiameter) is the indicator used for the coarse particle

standard.

PARTICLE POLLUTION

Trends in Pm2.5 concenTraTionsTere are two national air quality standards forPM

2.5: an annual standard (15 g/m3) and a 24-hour

standard (35 g/m3). Nationally, annual and 24-hourPM

2.5concentrations declined by 17 and 19 percent,

respectively, between 2001 and 2008, as shown inFigure 13.

Figure 13. National PM2.5

air qualitytrends, 2001-2008 (annual average

concentration and 98th percentile of24-hour concentration in g/m3).


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O u r N a t i o n s A i r 2 1

For each monitoring location, the maps inFigure 14 show whether annual and 24-hour PM

2.5

concentrations increased, decreased, or stayed aboutthe same since the beginning of the decade. Whencomparing two three-year periods, 2001-2003 and2006-2008, almost all of the sites show a decline orlittle change in PM

2.5concentrations. Sixteen sites in

California, Illinois, Indiana, Michigan, Ohio, Utah, andWest Virginia showed the greatest decreases in annualPM

2.5concentrations. Four of the 565 sites showed

an increase in annual PM2.5

concentrations greaterthan 1 g/m3. Tese sites were located in Montana,

Arizona, and Wisconsin. Of the four sites that showedan increase in annual PM

2.5concentrations, none were

above the level of the annual PM2.5

standard for themost recent three-year period of data (2006-2008). Five

sites in California, Montana, Oregon, Pennsylvania,and Utah showed decreases greater than 15 g/m3 in24-hour PM

2.5concentrations. Nineteen sites showed

an increase in 24-hour PM2.5

concentrations greaterthan 3 g/m3. Of the 19 sites that showed an increasefor the most recent three-year period of data, sevenmeasured concentrations above the level of the 24-hour

PM2.5 standard. Tese sites are located in or near thefollowing metropolitan areas: Virginia Beach, VA;Butte-Silver Bow, M; Nogales, AZ; Seattle, WA;

Albany, GA; Redding, CA; and Chico, CA (note:Virginia Beach was above the standard due to theeects of a wildre in North Carolina). Due to theinuence of local sources, it is possible for sites in thesame general area to show opposite trends, as in thecase of the Denver area for the 24-hour standard.

Figure 14. Change in PM2.5concentrations in g/m3, 2001-2003 vs.2006-2008 (3-year average of annualaverage and 98th percentile of 24-hourconcentrations).


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2 2 O u r N a t i o n s A i

In 2008, the highest annual average PM2.5

concentrations were in California, Arizona, andHawaii, as shown in Figure 15. Te highest 24-hourPM

2.5concentrations were in California and Virginia.

Wildres played a role in both states PM2.5

levels.

Some sites showed high 24-hour PM2.5

concentrations

but low annual PM2.5 concentrations, and vice versa.Sites that show high 24-hour concentrations but lowor moderate annual concentrations exhibit substantial

variability from season to season. For example, sites

in the Northwest generally show low concentrationsin warm months but are prone to much higherconcentrations in the winter. Factors that contribute tothe higher levels in the winter are extensive woodstoveuse coupled with prevalent cold temperature inversionsthat trap pollution near the ground. Nationally, moresites exceeded the level of the 24-hour PM

2.5standard

than the annual PM2.5 standard, as indicated by yellowand red dots on the maps below. Of the 18 sitesthat exceeded the annual standard and 55 sites thatexceeded the 24-hour standard, 14 sites exceeded both.

P a r t i c l e P o l l u t i o n

Figure 15. Annual average and 24-hour(98th percentile of 24-hour concentrations)

PM2.5 concentrations in g/m3, 2008.


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WeaTHer inFluences Pm2.5

In addition to emissions, weather plays an importantrole in the formation of PM

2.5. Figure 16 shows trends

in PM2.5

from 2001 through 2008, before and afteradjusting for weather. PM

2.5levels are monitored

throughout the year, and separate graphs are shown

Figure 16. Trends in annual, cool-month (OctoberApril) and warm-month (MaySeptember) average PM2.5

concentrationsin g/m3 (before and after adjusting for weather), and the location of urban monitoring sites used in the average.

for the warm and cool months. Tese separate graphsare shown due to the seasonal variability of thecomponents that make up PM

2.5, as described in

the next section. After adjusting for weather, PM2.5

concentrations have decreased by approximately17 percent in both the warm and cool seasons between2001 and 2008.


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Pm2.5

comPosiTion

Te chemical composition of PM2.5

is characterized interms of ve major components that generally comprisethe mass of PM

2.5: sulfate, nitrate, organic carbon

(OC), elemental carbon (also called black carbon, BC),and crustal material.

Figure 17 shows regional dierences in the compositionof PM

2.5nationwide. On average, sulfate is the largest

component by mass in the eastern U.S. Generally, thelargest sources of sulfate in the eastern U.S. are electricutilities and industrial boilers. OC is the next largestcomponent in the East. Te primary sources of OCare highway vehicles, non-road mobile, waste burning,

wildres, and vegetation. Next is nitrate; the largestsources of nitrate originate from highway vehicles,non-road mobile, electric utilities, and industrialboilers. Elemental carbon is a small component of the

overall PM2.5 composition (typically 5-10 percent in

U.S. cities). Elemental carbon is directly emitted fromincomplete combustion processes such as fossil fuel andbiomass burning. Crustal material is typically a smallfraction of PM

2.5mass, although two cities show higher

than average values (Birmingham, AL and Detroit,MI). Crustal material comes from suspended soil andmetallurgical operations.

In the West, OC is generally the largest estimatedcomponent of PM

2.5by mass. Fireplaces and

woodstoves are important contributors to OC in theWest. On an annual average basis, nitrate, sulfate,or crustal material can also represent substantialcomponents of PM

2.5for the western U.S. Te

composition varies from city to city and may vary bygeography. For example, in southern California andport cities in the Northwest, emissions from marine

vessels also likely contribute a signicant portion ofPM

2.5sulfate.

Figure 17. Four-season average of PM2.5

composition for 15 U.S. cities.


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Figure 18. PM2.5

composition by season for 15 U.S. cities.

It is important to note that although studies havebegun to focus on how dierent constituents ofparticulate matter (PM) may aect health outcomes,at this point there is no conclusive evidence thatany component is harmlessstudies continue tolink numerous components to health eects andthe evidence does not support excluding any PM

component or source from regulation. Tus, thoughdierent ambient mixtures of PM may be observedin dierent geographical areas and during dierentseasons, EPA continues to regulate PM

2.5and PM

10

by mass and most control strategies are designed toreduce mass rather than individual components fromparticular sources.

Te maps in Figure 18 reveal somewhat dierentpatterns between seasons. While sulfate is a majorcomponent in the eastern U.S. in the spring, fall, and(particularly) summer, the sulfate contribution during

winter is oset by larger amounts of nitrate in theMidwest and OC in the Southeast. Nitrate is lowerin the spring and fall, particularly in the southeastern

cities and is essentially zero during the summer inthe eastern U.S. Crustal material is a substantialsummertime component in Houston, X, and isgenerally low elsewhere in the East during all seasons.In the West, wintertime OC and elemental carbon aregenerally the largest components of PM

2.5, followed by

nitrate. Nitrate can represent a larger percentage in thespring and fall. Crustal material represents a relativelyhigh percentage year-round in arid Phoenix, AZ andDenver, CO.


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ParTicles eFFecTs on climaTe

Particles have both direct and indirect eects onclimate. Te direct eects come from particlesability to absorb and scatter light. Te dierenttypes of particles have dierent impacts onclimate: some warm (positive forcing); others cool

(negative forcing). Te net eect for all particles inthe atmosphere is cooling, as scattering generallydominates (National Academy of Sciences, 2005),though eects can vary dramatically by region.

Particles also have important indirect eectson climate. For example, dierent particles canincrease or decrease the reectivity of clouds,leading to cooling or warming eects. Particlesalso inuence cloud lifetime and precipitation, andmay aect droughts, rainfall, and stream ows.However, there remains relatively high scientic

uncertainty about these indirect eects (NationalAcademy of Sciences, 2005).

As shown in Figure 19, the direct eects ofparticles on climate are signicant even whencompared to carbon dioxide (CO

2), the most

important greenhouse gas. However, the directionof the climate impact from particles (warming vs.

Figure 19. Net radiative forcing ( Watts per m2) associated withthe presence of dierent pollutants in the atmosphere, based onconcentrations in 2005 compared to pre-industrial levels. (Source:Black carbon data [IPCC, 2007]. Carbon dioxide, organic carbon,sulfates data [National Academy of Sciences, 2005].)

cooling) varies by particle type and location of emission, whichmakes designing control strategies more challenging. Sourcesemitting BC also emit OC and may emit NO

xand SO

2, all of

which form particles that tend to have a cooling eect. Tus,while the health benets of reducing all types of emissions

reTroFiTTing diesel engines

From the farm to the interstate highway to the neighborhood grocery store,diesel engines are found in every corner of society. Despite EPAs stringentdiesel engine and fuel standards, which, for new engines, are being phasedin over the next decade, 20 million engines already in use continue to emitrelatively large amounts of oxides of nitrogen (NO

X) and fine particulate matter

(PM2.5

). Both of these pollutants contribute to serious health conditions, such asasthma, and worsen heart and lung disease. In addition, diesel engines emitblack carbon and carbon dioxide, which contribute to global climate change.

Fortunately, a variety of cost-effective technologies can dramatically reduceharmful emissions, save fuel, and help our nation meet its clean air andsustainability goals. In 2000, to address the concerns of both new and existingdiesel engines, EPA created the National Clean Diesel Campaign (NCDC), a

partnership program that incorporates traditional regulatory approaches andinnovative non-regulatory approaches to achieve results.

In 2008, for the f irst time, Congress appropriated funding under the EnergyPolicy Act of 2005 to reduce emissions from diesel engines in the nationsexisting fleet. In the first year of the program, the EPAs NCDC distributed $49.2million to initiate diesel emission reduction projects and programs across the country. In addition, the American Recoveryand Reinvestment Act of 2009 provided $300 million in new funding for national and state programs to support theimplementation of verified and certified diesel emissions reduction technologies.

As a result of this funding and NCDC projects across the country, hundreds of thousands of tons of pollutants and air toxicswill be reduced over the lifetime of the program.


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undersTanding linKages BeTWeen BlacK carBon and climaTe

Black carbon (BC) is emitted directly as a result ofincomplete combustion of fuels, generally from man-madesources. Many BC particles are too small to be visible.One-half to two-thirds of BC emissions in the U.S. comefrom the burning of fossil fuels, while the remainder comesfrom biomass burning. Unless specifically controlled, dieselengines are major producers of BC.

BC emissions are a component of fine particle pollution,which causes adverse health effects. BC emissions alsolead to climate warming by absorbing incoming andreflected sunlight in the atmosphere (direct effects) andby darkening clouds, snow, and ice, thereby reducingthe reflection of light back into space (indirect effects).Other effects may include changes in precipitation andcloud patterns. The total climate impact of BC currentlyin the atmosphere has been estimated to be anywherefrom 10 percent to more than 60 percent as large as theclimate impact from carbon dioxide (CO

2). These effects

may be concentrated in regions such as the Arctic andthe Himalayas, where glaciers provide critical fresh waterreservoirs for nearly 1.3 billion people.

Actions taken to reduce emissions of BC could producealmost immediate benefits for climate: while CO

2remains

in the atmosphere for decades to centuries, freshly emittedBC is in the atmosphere for a very short time. Reducing BC

(1) Sunlight absorbed by BC particles warms the air.(2) Other types of particles scatter or reflect light andcool the atmosphere.

(3) Sunlight absorbed by BC and some otherparticles on snow speeds up melting and results in lesssunlight reflected.

today may reduce climate forcing in the near term.

Considerable uncertainty remains regarding the levels of BC emissions from various sources, the transport of theseemissions around the globe, and the net impacts of BC and co-emitted pollutants such as organic carbon on the Earthsenergy balance and global climate patterns.

Figure 20. National PM10

air quality trend, 2001-2008(second maximum 24-hour concentration in g/m3).

contributing to ambient PM arerelatively clear, the net climate impactof PM emissions reduction strategies

will depend on the relative amountsof each of these components reducedfrom controlled sources.

Trends in Pm10concenTraTions

Nationally, 24-hour PM10

concentrations declined by 19 percentbetween 2001 and 2008, as shown inFigure 20.


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Figure 22. PM10

concentrationsin g/m3, 2008 (second maximum

24-hour concentration).

Note: 2563 (g/m3) is from a site located inthe Mono Basin nonattainment area where the

major source of PM10

is from a dry lake bed(Mono Lake).

Figure 21. Change in PM10

concentrations in g/m3, 2001-2003vs. 2006-2008 (3-year averageof second maximum 24-hourconcentrations).

When comparing two 3-year periods, 2001-2003 and2006-2008, most sites showed a decline or little changein PM

10, as shown in Figure 21. wenty-seven sites

located in the Southwest, South Carolina, Missouri,Wyoming, and Montana showed a decline greaterthan 50 g/m3. Ninety-one sites showed an increaseof greater than 10 g/m3 over the trend period. Five

of these sites (Houston, X; Albany, GA; Phoenix,

AZ; Butte-Silver Bow, M; and rinity County, CA)showed large increases of 50 g/m3 or more.

Figure 22 shows that in 2008, the highest PM10

concentrations were located in California, Arizona, andNew Mexico. Within these areas some sites showed adecline greater than 50 g/m3. Highest concentrations

are largely located in dry and/or industrial areas with ahigh number of coarse particle sources.


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cooKsTove PolluTion THreaTens PuBlic HealTH and climaTe

Roughly half of the worlds populationespecially in Asia, Africa, and parts ofLatin Americauses wood, dung, coal,or other solid fuels for cooking and

heating. This leads to extraordinarilyhigh indoor concentrations of fineparticle pollution, carbon monoxide,and other toxic pollutants. The WorldHealth Organization estimatesthat indoor stove use leads to anestimated 1.5 million prematuredeaths each year, mostly amongwomen and young children, makingit the fourth most serious health riskfactor in poor developing countriesafter undernourishment, unsafe sex,and unsafe water, sanitation, and

hygiene. Fuel wood collection alsolimits economic and educationalopportunities for women and childrenand can put substantial pressure onlocal forests and ecosystems.

Use of clean and efficient cookstoves and fuels would significantly improve public health and could also provide importantclimate benefits. It is estimated that an improved cookstove typically reduces carbon dioxide-equivalent emissions by 1 to4 tons per yearalmost as much as taking a typical U.S. car of f the road. Crude, traditional cookstoves account for about aquarter of global black carbon emissions, which contribute to regional and global warming, though the net climate impact

also depends on co-emissionsof other (primarily reflecting)particles.

In 2002, the EPA and13 partners launched thePartnership for Clean IndoorAir (PCIA) to help householdsadopt clean cooking andheating practices to improvehealth, livelihood, andquality of life. Today, PCIAhas over 310 active partnerorganizations working inover 115 countries aroundthe world (http://www.

PCIAonline.org). Already,key PCIA partners havereported helping 2.4 millionhouseholds adopt cleancooking and heatingpractices, reducing harmfulexposures for more than18 million people.

An unvented, traditional stove in Ethiopia produces high indoor smoke levels fora woman and young child. (Credit: John Mitchell, U.S. EPA)

An improved plancha stove with a chimney in Guatemala significantly lowers indoorsmoke levels. (Credit: Richard Grinnell, HELPS International, http://www.helpsintl.org)

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