# The Particle Pollution Report Current Understanding of Air Quality and Emissions through 2003 **United States Environmental Protection**  **Agency**

99 00 01 02 03 30

20

10

0Concentration,μg/m3 **1999–2003: -10%**

National Standard

A verage 

### PM **2.5** 

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

### EPA 454-R-04-002 December 2004



# The Particle Pollution Report
Current Understanding of Air Quality and Emissions through 2003

Contract No. 68-D-02-065 W

ork Assignment No. 2-01

U .S. Environmental Protection Agency Office of Air Quality Planning and Standards Emissions, Monitoring, and Analysis Division

Research Triangle Park, North Carolina

### Contents

Introduction ii

Major Findings 1

Understanding Particle Pollution 2 Particle Pollution Is... 2 Complex 2 A Continuum of Sizes 2 Made Up of Many Species 3 Seasonal 4 Both Local and Regional 8

Particle Pollution in 2003 10 PM 10 

### – PM 2.5 

### 12 Looking at Trends 13 PM 10 

### National and Regional Trends 13 PM 2.5 

### National and Regional Trends 14 25-year PM 2.5 

### T rends 16 Rural Sulfate Trends 18

Explaining the Trends 20 Regional PM 2.5 

### T rends in Three

Regions (1999-2003) 20 Effect of Meteorology 21 The PM 2.5 

### Remainder 22 Control Programs 23

The Future 25 Upcoming PM 2.5 

### Designations 26 PM 2.5 

### and Other Pollutants 26 

# Introduction

From the black puff of smoke from an old diesel bus to the haze that obscures the view in our national parks, particle pollution affects us all. This complex pollutant is present y ear-round, both in our cities and in the countryside, and it can cause health problems for millions of Americans. EPA’s national air quality standards for particle pollution are designed to protect public health and the environment. As this report shows, we are seeing progress: levels of particle pollution are decreasing on a national scale. Yet millions of people still live in areas of the country where particle pollution levels exceed national air quality standards. This harmful 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 steps that will reduce particle emissions and formation. These efforts range from EPA’s Acid Rain program and regulations

r educing emissions from fuels and diesel engines, to implementation of the Agency’s first fine particle standards and a proposed rule to reduce particle-forming emissions from power plants. In this report, EPA

■ 

## Explores characteristics of particle pollution in the

United States

■ 

## Analyzes particle pollution for 2003 (the most recent

y ear of data)

■ 

## Summarizes recent and long-term trends

■ 

## Investigates the relationship between air quality and emissions

■ 

## Reviews some current programs and future prospects for

r educing particle pollution levels. In addition, text boxes in this report present information on more specialized areas of interest, such as the PM Supersite project, episodic events, satellite monitoring, and the relationship of particle pollution to other air pollutants.

**ii**

### 1 

# Major Findings

Air Quality Improvements

■ 

## Pa r ticulate 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 monitoring began in 1999 – h av e decreased 10% since 1999

– a re 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 – h av e declined 7% since 1999 – h av e declined 31% since 1988.

■ 

## In 2003, 62 million people lived in 97 U.S. counties with monitors showing particle pollution levels higher than the PM 2.5 

## air quality standards, the PM 10 

## standards, or both.

■ 

## Monitored levels of both PM 2.5 

## and PM 10 

## generally decreased the most in areas with the highest concentrations. For example, PM 2.5 

## levels decreased 20% in the Southeast from 1999 to 2003. The Northwest showed a 39% decrease in PM 10 

## levels from 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 transformation of sulfur dioxide and nitrogen oxide gases. Carbon compounds can be directly emitted, or they can form in the atmosphere from organic

v apors.

■ 

## Approximately one-third of the PM 2.5 

## improvement observed in the eastern half of the country can be attributed to reduced sulfates; a large portion of the

r emaining PM 2.5 

## improvement is attributable to

r eductions in carbon-containing particles, especially in the Industrial Midwest and the Southeast. ■ 

## P ow er plant emissions of sulfur dioxide dropped 33% from 1990 to 2003, largely as a result of EPA’s Acid Rain program. These reductions yieldedsignificant regional reductions in sulfate concentrations, reducing acid deposition and improving visibility.

■ 

## Nationwide, reductions in industrial and highway

v ehicle emissions of fine particles and volatile organic compounds appear to have contributed to the improvement in PM 2.5 

## .

■ 

## In the eastern half of the country

– r egional pollution accounts for more than half of the measured PM 2.5 

## . This regional pollution comes 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 rural areas. Power plants are the largest contributor to this sulfate formation.

■ 

## In the Industrial Midwest, Northeast, and southern California, nitrates make up a large portion of PM 2.5 

## , especially in winter. Average nitrate concentrations in urban areas are generally higher than nearby rural levels. Power plants and highway

v ehicle emissions are large contributors to nitrate formation.

■ 

## EPA and states have put in place a number of control programs that will continue to reduce particle-forming emissions. EPA’s 2004 Clean Air Nonroad Diesel Rule will significantly reduce emissions from nonroad diesel equipment across the country. EPA’s proposed Clean Air Interstate Rule(proposed December 2003) will reduce PMforming emissions from power plants in the eastern United States.

# Complex

P erhaps no other pollutant is as complex as particle pollution. Also called particulate matter or PM, particle pollution is a mixture of solid particles 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 the naked eye. Others are so small, they can only be detected 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 emitted directly from a source, while others form incomplicated chemical reactions in the atmosphere. And some can change back and forth from gas to particle form. Particle pollution also

va r ies by time of year and by location and is affected by several aspects of weather, such as temperature, 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** 

# Pa r ticle Pollution Is... A Continuum of Sizes In general, particle pollution consists of a mixture of larger materials, called “coarse particles,” and smaller particles, called “fine particles.” Coarse particles have diameters ranging from about 2.5 micrometers (μm) to more than 40 μm, while fine particles, also known as known as PM 2.5 

## , include particles with diameters equal to or smaller than 2.5 μm. EPA also monitors and

r egulates PM 10 

## , which refers to particles less than or equal to 10 μm in diameter. PM 10 

## includes coarse particles that are “inhalable” — particles ranging in size from 2.5 to 10 μm that canpenetrate the upper regions of the body’s respiratory defense mechanisms. “Ultrafine” particles are a subset of PM 2.5 

## , measuring less than 0.1 μm in diameter.

### 3 

# Made Up of Many Species

Pa r ticles are made up of different chemical components. The major components, or species, are carbon, sulfate and nitrate compounds, and crustal materials such as soil and ash. The different components that make up particle pollution come from specific sources and are often formed in the atmosphere (see “Sources and Transport of Particle Pollution” on page 6). The chemical makeup of particles varies across

Sulfates Nitrates Carbon Crustal 

### Northwest

**Southern California**  **Southeast Industrial**  **Midwest Northeast** 

**Southwest Upper**  **Midwest**

Circle size corresponds to PM 2.5 concentration. 

### WEST EAST 

### Figure 2. Average PM **2.5** 

### composition in urban areas by region, 2003.



## Note: In this report, the term“sulfates” refers to ammonium sulfate and “nitrates” refers to ammonium nitrate.“Carbon” refers to total carbonaceous mass, which is the sum of estimated organic carbon mass and elemental carbon.“Crustal” is estimated using the IMPROVE 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 reg ions used in EPA’s 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 United States contain more sulfates than those in the W est, while fine particles in southern California contain more nitrates than other areas of the country. Carbon is a substantial component of fine particles everywhere. (For information on the composition of ultrafine and coarse particles in Los Angeles, see page 7.)

**Health Effects** Exposure to particles can lead to a variety of serious health effects. The largest particles do not get very far into the lungs, so they tend to cause fewer harmful health effects. Coarse and fine particles pose the greatest problems because they can get deep into the lungs, and some may even get into the bloodstream. Scientific studies show links between these small particles and numerous adverse health effects. Long-term exposures to PM, such as those experienced by people livingfor many years in areas with high particle levels, are associated with problems such as decreased lung function, development of chronic bronchitis, and premature death. Short-term exposures to particle pollution (hours or days) are associated with a range of effects, including decreased lung function, increased respiratory symptoms, cardiac arrythmias (heartbeat irregularities), heart attacks, hospital admissions or emergency room visits for heart or lung disease, and premature death. Sensitive groups at greatest risk include people with heart or lung disease, older adults, and children. 

### Environmental Effects Fine particles are the major source of haze that reduces visibility in many parts of the United States, including our national parks. PM affects vegetation and ecosystems by settling on soil and water, upsetting delicate nutrient and chemical balances. PM also causes soiling and erosion damage to structures, including culturally important objects such as monuments and statues. 

### Health and Environmental Effects of Particulate Matter 

# Pa r ticle Pollution Is...

### 4 

# Seasonal Fine particles often have a seasonal pattern. PM 2.5 

## v alues in the eastern half of the United States are typically higher in the third calendar quarter (July-September) when sulfates are more readily formed from sulfur dioxide (SO 2 

## ) emissions frompower plants in that region. Fine particle concentrations tend to be higher in the fourth calendar quarter in many areas of the West, in part because fine particle nitrates are more readily formed in cooler weather, and wood stove and fireplace use produces more carbon. The time of year also influences daily fine particle patterns. Unlike daily ozone levels, which are usually elevated in the summer, daily PM 2.5 

## v alues at some locations can be high at any time of the y ear. 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), EPA’s tool for informing the public about air pollution levels in their communities. As the Fresno graphic illustrates, fine particles can be elevated in the fall and winter in some areas, while ozone is elevated only in the summer. Contrast the Fresno graphic with the Baltimore graphic, which shows PM elevated year-round. Note: Elevated levels on the AQI do not indicate that an area is violating EPA’s national air quality standards for any particular pollutant. The AQI is designed to help people reduce their individual exposure to pollution.

0 5 10 15 20 25 0 5 10 15 20 25

0 5 10 15 20 25

0 5 10 15 20 25

0 5 10 15 20 25 0 5 10 15 20 25

0 5 10 15 20 25



### Oct-Dec Jul-Sep Apr-Jun Jan-Mar 

### Northwest

**Southern California**  **Upper Midwest** 

**Southeast Industrial**  **Midwest Northeast** 

**Southwest**PM2.5Mass,μg/m3PM2.5Mass,μg/m3PM2.5Mass,μg/m3PM2.5Mass,μg/m3PM2.5Mass,μg/m3PM2.5Mass,μg/m3PM2.5Mass,μg/m3 

### Figure 3. Seasonal averages of PM **2.5** 

### concentration by region, 1999–2003. 

# Pa r ticle Pollution Is...The AQI is an index for reporting daily air quality. It tells how clean or polluted the air is and what associated health effects might be a concern. The AQI focuses on health effects people may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major pollutants regulated by the Clean Air Act: particulate matter, ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI values for particulate matter are shown here. 

### Air Quality Index (AQI) - Particulate Matter

**5 PM**  **2.5** 

### PM **10** 

### AQI (μg/m 3 

### ) ( μg/m 3 

### ) **Air Quality Descriptor**
0–50 0.0–15.4 0–54 Good
51–100 15.5–40.4 55–154 Moderate 101–150 40.5–65.4 155–254 Unhealthy for Sensitive Groups 151–200 65.5–150.4 255–354 Unhealthy 201–300 150.5–250.4 355–424 Very unhealthy

Ozone PM 2.5 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

Date

JAN FEB MAR APR MAY JUN JUL AUG S EP OCT NOV DEC JAN Very Unhealthy

Unhealthy

Unhealthy for Sensitive Groups

Moderate

GoodAir Quality Index (AQI) 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300

Date

JAN FEB MAR APR MA Y JUN JUL AUG S EP O CT NOV DEC JAN Very Unhealthy

Unhealthy

Unhealthy for Sensitive Groups

Moderate

Good **Fresno, CA**Air Quality Index (AQI)

**Baltimore, MD**



## 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.

### V **isibility**

**6 Sources**  Particulate matter includes both “primary” PM, which is directly emitted into the air, and “secondary” PM, which forms indirectly 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 of these reactions require sunlight and/or water vapor. Secondary PM includes

• Sulfates formed from sulfur dioxide emissions from

power plants and industrial facilities

• Nitrates formed from nitrogen oxide emissions from cars,

trucks, and power plants

• Carbon formed from reactive organic gas emissions from

cars, trucks, industrial facilities, forest fires, and biogenic sources such as trees. Cars, trucks, heavy equipment, wild fires, waste burning, and biogenics

Power generation

Suspended soil and metallurgical operations

Cars, trucks, and power generation **Carbon Crustal** 

**Sulfates Nitrates**  **Automobiles, Power Generation, and Other**

**Sources Contribute to Fine Particle Levels T** 

**ransport** In the atmosphere, coarse and fine particles behave in different ways. Larger coarse particles may settle out from the air more rapidly than fine particles and usually will be found relatively close to their emission sources. Fine particles, however, can be transported long distances by wind and weather and can be found in the air thousands of miles from where 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 nitrates that 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 country’s best-known and mosttreasured national parks and wilderness areas. Visibility impairment occurs when fine particles scatter and absorb light, creating a haze that limits the distance we can see and that degrades the color, clarity, and contrast of the view. The particles that cause haze are the same particles that contribute to serious health problems and environmental damage. V isibility impairment—and the concentration of particles that cause it—generally is worse in the eastern United States than it is in the West. Humidity can significantly increase visibility impairment by causing some particles to become more efficient at scattering light. Average relative humidity levels are higher in 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 is primarily the result of high sulfate concentrations, combined with high humidity. Sulfates, which dominate the composition of these visibility-impairing particles, have been found to contribute even more to light extinction than they do to fine particle concentrations. In the West, organic carbon, nitrates, and crustal material make up a larger portion of total particle concentrations than they do in the East. Through its 1999 regional haze rule, EPA, states, and other federal agencies are working to improve visibility in 156 national parks and wilderness areas such as the Grand Canyon, Y

osemite, the Great Smokies, and Shenandoah. Five multistate regional planning organizations are working together to develop and implement regional haze reduction plans. For more 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. Y

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

### 7 After issuing the nation’s first PM 2.5 standards in 1997, EPA developed the PM Supersites project, a monitoring research program, to address a number of scientific issues associated with particulate matter. Program goals focus on obtaining atmospheric measurements to

• Characterize PM, its constituents, atmospheric transport, and source categories that affect PM in any region

• Compare and evaluate different PM measurement

methods (e.g., emerging sampling methods, routine monitoring techniques)

• Support exposure and health effects research

concerning the relationships between sources, ambient PM concentrations, and human exposures and health effects and the biological basis for these relationships. EPA selected eight locations for Supersites, including Los Angeles. Atmospheric measurements taken at the Los Angeles site between October 2002 and September 2003 show that ultrafine particles make up a small portion of the PM concentration compared to inhalable coarse and fine particles. However, the number of ultrafine particles is significantly larger than the number of coarse or fine particles. EPA is studying this from a health perspective.The Los Angeles data also show that coarse, fine, and ultrafine 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 here as organic and elemental carbon, makes up a large fraction of ultrafine and fine PM in Los Angeles. For more information, see www.epa.gov/ttn/amtic/supersites.html and www.epa.gov/ttn/amtic/laprog.html 

### PM Supersites

**Los Angeles, CA (University of Southern California Site)** 

Oct 02 Nov 02 Dec 02 Jan 03 Feb 03 Mar 03 Apr 03 May 03 Jun 03 Jul 03 Aug 03 Sep 03 0 10 20 30 40 50 60Mass,μg/m3

Ultrafine Fine Coarse 

### Ultrafine Particles (<0.1 μ **m)**

**Fine Particles (<2.5** μ **m)**

**Particles 2.5 to 10** μ **m** Nitrates Sulfates Metals Organic Carbon Elemental Carbon



## Note:“Crustal materials” include windblown soil, industrial process emissions, sea salt, and flyash from combustion.

### 8 

# Both Local and Regional Both local and regional sources contribute to particle pollution. Figure 5 shows how much of the PM 2.5 

## mass can be attributed to local versus

re g ional sources for 13 selected urban areas (arranged west to east). In each of these urban areas, monitoring sites were paired with nearby

r ural sites. When the average rural concentrationis subtracted from the measured urban concentration, the estimated local and regional contrib utions become apparent. In the East, regional pollution contributes more than half of total PM 2.5 

## concentrations. Rural background PM 2.5 

## concentrations are high in the East and are somewhat uniform over large geographic areas. These regional concentrations come from emission sources such as power plants, natural sources, and urban pollution and can be transported hundreds of miles.

**Measured PM 2.5**  

### Concentration

Missoula Salt Lake City T ulsa St. Louis Birmingham Indianapolis Atlanta Cleveland Charlotte Richmond Baltimore New York City

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

**WEST EAST** 

Regional Contribution Local Contribution 

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

### . 

## F or the cities shown in Figure 5, local contributions range from 2 to 20 micrograms per cubic meter (μg/m 3 

## ), with the West generally showing larger local contributions than the East. In the East, local contributions are generally greatest in cities with the highest annual average PM 2.5 

## concentrations.Figure 6 shows the local and regional contrib utions for the major chemical components that make up urban PM 2.5 

## : sulfates, carbon, and nitrates. In the eastern United States, the local contribution of sulfates is generally small. Most sulfates in the East are converted from regional SO 2 

## emissions and are transported long distances from their sources. Carbon has the largest local contribution of the three major chemical components. These local emissions come from a combination of mobile and stationary combustion sources. The regional

Note: Urban and nearby rural PM 2.5 

## concentrations suggest substantial regional contributions to fine particles in the East.The measured PM 2.5 

## concentration is not necessarily the maximum for each urban area. 

# Pa r ticle Pollution Is...

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

### 9 **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 and trucks.

Missoula Salt Lake City T ulsa St. Louis Birmingham Indianapolis Atlanta Cleveland Charlotte Richmond Baltimore New York City

0 6 10 12 Fresno

**WEST EAST** 

Regional Contribution Local Contribution

4 2 8 

### Sulfates

Annual Average Concentration of Sulfates, μ g/m 3 

### Carbon

Missoula Salt Lake City T ulsa St. Louis Birmingham Indianapolis Atlanta Cleveland Charlotte Richmond Baltimore New York City

0 6 10 12 Fresno

**WEST EAST** 

Regional Contribution Local Contribution

4 2 8 Annual Average Concentration of Carbon, μ g/m 3

Missoula Salt Lake City T ulsa St. Louis Birmingham Indianapolis Atlanta Cleveland Charlotte Richmond Baltimore New York City

0 6 10 12 Fresno

**WEST EAST** 

Regional Contribution Local Contribution

4 2 8 

### Nitrates

Annual Average Concentration of Nitrates, μ 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 is likely 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.≤ 10 10.1 - 15 15.1 - 20 > 20 

### PM **2.5** 

### , 2003

Concentration range ( μ g/m 3 )



### 10 

## concentrations greater than the PM 10 

## or PM 2.5 

## national air quality standards. Thirty-seven counties (21 million people) measured concentrations in excess of the national PM 10 

## standards, and 72 counties (53 million people) exceeded the national PM 2.5 

## standards. These numbers do not include other areas outside of these counties that might contribute to levels above the standards. Figure 7 shows the range of PM 10 

## concentrationsacross the country in 2003. The highest concentrations were recorded in Inyo and Mono counties, California; El Paso County, Texas; and Dona Ana County, New Mexico. Figure 8 shows the Nationally, fine particle concentrations in 2003

we re the lowest since nationwide PM 2.5 

## monitoring began in 1999. Compared with 2002, the biggest decreases occurred in the Industrial Midwest and parts of California — areas with

r elatively high PM 2.5 

## concentrations. PM 10 

## concentrations were slightly higher in 2003 than the previous year, but they are still the second lowest since nationwide PM 10 

## monitoring began in 1988. Although average concentrations have declined nationally, many areas still exceed the level of the PM standards. In 2003, monitors in 97 counties (home to 62 million people) showed 

# Pa r ticle Pollution in 2003

Concentration range ( μ g/m 3 )

≤ 54 55 - 154 155 - 354 > 354



### Figure 8. PM **2.5** 

### concentrations, 2003 (annual average). **Figure 7. PM 10**  

### concentrations, 2003 (second maximum 24-hour).



## Note: Circle size corresponds to PM 2.5 

## concentration range.

### 11 

## range of 2003 PM 2.5 

## annual averages across the country. The highest annual averages occurred in southern California and Pittsburgh. High levels are also seen in many urban areas in the Southeast, Nor theast, and Industrial Midwest. See www.epa.gov/airtrends/pm.html for county-level maps of PM.
PM 2.5 

## concentrations can reach unhealthy levels

ev en in areas that meet the annual standard. In 2003, there were 277 counties with at least 1 unhealthy day based on PM 2.5 

## A QI values, as shown in Figure 9. Nearly two-thirds of those counties had annual averages below the level of the standard. Figure 10 shows how several major metropolitan areas fared in 2003 relative to previous years. Most metropolitan areas had fewer unhealthy PM 2.5 

## days in 2003 compared to the

av erage from the previous 3 years, which reflects the improvements observed in 2003.

Number of AQI Days Above 100

None 1 - 5 6 - 10 11 - 30 > 30 

### Figure 9. PM **2.5** 

### AQI days above 100 ( ≥ **40.5 μg/m 3**  

### ) in 2003.

New York

Washington, DC Cincinnati Chicago

St. Louis

Birmingham Atlanta Minneapolis

Charlotte

Dallas Fresno Sacramento Salt Lake City

Phoenix Denver Missoula Seattle

Number of days (2000-2002, average) Number of days (2003)

7 2

2 1

14 3 6
3 1

10 13

0 3

1 21

1 1 0

13 6

8 4 13 7

21

6 11 9 2 2 12 5 9 6 

### Figure 10. Number of days with PM **2.5** 

### AQI levels above 100, 2003 versus average 2000–2002. 

## 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.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 replaced by PM 10 . In 1997, EPA revised the primary (health) and secondary (welfare) PM NAAQS by adding standards for PM 2.5 . E PA added PM 2.5 standards because fine particles are 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**  **PM 10**  Short-term 65 μg/m 3 150 μg/m 3 (24-hour average) Long-term 15 μg/m 3 50 μg/m 3 (annual average)



### 12 

## PM **10** 

## – PM **2.5** 

## Pa r ticulate matter varies greatly in size. “Coarse” particles can be as large as 40 micrometers (μm) in diameter or even larger. EPA's National Ambient Air Quality Standards (NAAQS) for particulate matter, however, have focused on particles that are 10 μm in diameter or smaller. These particles are the most likely to be inhaled and can penetrate into the lower respiratory tract. EPA has had air quality standards for particles 10 μm and smaller since 1987. In 1997, EPA also established an NAAQS for fine particles — those particles 2.5 μm in diameter or smaller. EPA is now in the process of reviewing the PM NAAQS. As shown in Figure 11, the size distribution of particles smaller than 10 μm but larger than 2.5 μm varies by geographic location. Levels of PM 10-2.5 

## are generally higher in the West, particularly the Southwest. PM 10-2.5 

## typically comprises more than half of the PM 10 

## mass in the West. Data also suggest that concentrations of particles between 2.5 and 10 μm in size are lower in the mid-Atlantic and Southeast. Overall, while directly emitted PM 2.5 

## and its precursors can come from both local and regional sources, the larger particles that are part of PM 10 

## tend to come from local sources.

**Figure 11. Percent of 2003 annual average concentration of particles smaller than 10 μm but larger than 2.5 μm, by region.** 

**National Standards for Particulate Matter**

**Compliance** Each PM standard carries a separate threshold for compliance:

• 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 98th percentile of 24-hour concentrations.

• The short-term standard for PM 10 is not to be exceeded

more than once per year, averaged over 3 years. EPA reviews the NAAQS on a regular basis. The standards for PM 10 and PM 2.5 are currently under review, to be completed in 2006.Northwest Southern CA Southwest Ind. Midwest Upper Midwest Northeast Southeast PM 2.5 PM 10-2.5 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% WEST EAST



## Note: μg/m 3 

## = micrograms per cubic meter.

### 13 

## PM **10** 

## National and Regional Trends Nationally, PM 10 

## concentrations have decreased 31% since 1988, as shown in Figure 12. Regionally, PM 10 

## decreased most in areas with historically higher concentrations — the Northwest (39%), the Southwest (33%), and southern California (35%). Programs aimed at reducing direct emissions of particles have played an important role in

r educing PM 10 

## concentrations, particularly in w estern areas. Some examples of PM 10 

## controls include paving unpaved roads, replacing wood and coal with cleaner-burning fuels like natural gas, and using best management practices for agricultural sources of resuspended soil. Additionally, EPA’s Acid Rain Program has substantially reduced SO 2 

## emissions from power plants since 1995 in the eastern United States, contributing to lower PM concentrations. Direct emissions of PM 10 

## have decreased approximately 25% nationally since 1988.

90 91 92 93 94 95 96 97 98 99 00 01Concentration,μg/m3 **NAAQS**

10% of sites have concentrations below this line 90% of sites have concentrations below this line



### 1988–2003: 31% decrease **1999–2003: 7% decrease** 02 03 434 Monitoring Sites

A

verage

0 10 20 30 40 50 60

89

88 0 1 2

94 96 98 00 02Yearly Emissions, Million Tons

88 90 92 4

3

03 

### 1988–2003: approximately 25% decrease **1999–2003: 3% decrease** Fuel Combustion T ransportation Industrial Processes

89 91 93 95 97 99 01 In 1996, EPA refined its methods for estimating emissions. **Northwest**

**Southern California** 
**Southeast Industrial**  **Midwest Northeast** 

**Southwest**

National Standard: 50 μ g/m 3 Regional Trend 

### 39% 35.5 21.5



### 29% 34.2 24.3 

### 29% 28.8 20.5



### 25% 32.9 24.6 

### 33% 39.5 26.5 

### 35% 42.3 27.6 **Upper Midwest** 



### 16% 35.8 29.9 

### Annual Average PM **10** 

### Concentrations, 1988–2003

**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, **1988–2003.**

### 14 

## PM **2.5** 

## National and Regional Trends
PM 2.5 

## concentrations have decreased 10% nationally since 1999. Generally, PM 2.5 

## has decreasedthe most in regions with the highest concentrations — the Southeast (20%), southern California (16%), and the Industrial Midwest (9%), as shown in Figure 13. With the exception of the Northeast, the remaining regions posted modest declines in PM 2.5 

## from 1999 to 2003. A variety of local and national programs have

r esulted in a 5% decrease in estimated direct emissions of PM 2.5 

## ov er the past 5 years. In addition, programs that reduce the gaseous emissions that can form particles in the atmosphere have yielded additional reductions. National programs that affect regional emissions — including EPA’s Acid Rain Program — have contributedto lower sulfate concentrations and, consequently, to lower PM 2.5 

## concentrations, particularly in the Industrial Midwest and Southeast. National ozone-reduction programs designed to reduce emissions of volatile organic compounds (VOCs) and nitrogen oxides (NO

x 

## ) also have helped reduce carbon and nitrates, both of which are components of PM 2.5 

## . Nationally, SO 2 

## , NO

x 

## , a nd VOC emissions decreased 9%, 9%, and 12%, respectively, from 1999 to 2003. In eastern states affected by the Acid Rain Program, sulfates decreased 7% over the same period.

### 15 **Northwest**

**Southern California**  **Upper Midwest** 

**Southeast Industrial**  **Midwest Northeast** 

**Southwest**

National Standard: 15 μ g/m 3 Regional Trend 9.0 10.5 

### 15% 10.7 11.4 

### 6% 14.1 15.6 

### 9% 13.4 13.2 

### 1%

12.6 15.7 

### 20% 16.9 20.0


### 16% 8.1 8.7 

### 7% 

### Figure 13. Regional and national trends in annual average PM **2.5** 

### concentrations and emissions
**r elated to PM**  **2.5** 

### formation, 1999–2003.

**Annual Average PM 2.5**  

### Concentrations, 1999–2003

99 00 01 02 03 30

20

10

0Concentration,μg/m3

**NAAQS**

10% of sites have concentrations below this line 90% of sites have concentrations below this line 780 Monitoring Sites

A

verage

**10% Decrease**Yearly Emissions, Thousand Tons **9%**

**5% 9%** 

**12%** 

### National PM **2.5**



### Air Quality **National PM 2.5**  

### and Precursor Emissions

**PM 2.5** 

Fuel Combustion Industrial Processes Transportation **VOC NO**  **x SO**  **2** 30

25

20

15
10

5
0 99 00 01 02 03

30

25

20

15
10

5
0 99 00 01 02 03 3

2

1

0 99 00 01 02 03 30

25

20

15
10

5
0 99 00 01 02 03

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 ammonia emission estimates, its trends are not shown here.

### 16 

## y ears, average PM 2.5 

## levels in 2003 were the lowest on record. Low-sulfur gasoline use and ozone reduction programs designed to control NO

x 

## and VOC emissions may have contributed to the PM 2.5 

## decrease observed in the 1990s.

■ 

## W ashington, DC: PM 2.5 

## concentrations are currently (2003) at their lowest levels. The

r elatively large drop from 1994 to 1995 corresponds to decreases in sulfates (21%) and organic carbon (30%). The decrease in sulfates is attributable in part to the Acid Rain Program, which substantially reduced SO 2 

## emissions from power plants during this time. The decrease in organic carbon is attributable in part to the use of reformulated gasoline.

■ 

## Chicago: PM 2.5 

## concentrations at this site

have dropped substantially since the early 1980s, reaching their lowest levels in 2003.
F or additional information on long-term trends, see www.epa.gov/airtrends/pm.html. 

## 25-Year PM **2.5** 

## Tr **ends** Because EPA’s national PM 2.5 

## monitoring network is just 5 years old, we use data from older PM 2.5 

## monitoring networks to assess longer-term trends. Although the earlier networks are more limited in geographic scope and years of coverage, their data do provide historical perspective. The maps in Figure 14 show how PM 2.5 

## concentrations 25 years ago compare with PM 2.5 

## concentrations today in 39 major cities. Reductions vary among the 39 cities. Generally, the largest reductions occurred in the areas with the highest concentrations. On

av erage, today’s levels are about 30% lower than they were 25 years ago. The following examples, illustrated in Figure 14, show how PM 2.5 

## concentrations have improved

ov er the past 25 years in three cities. Figure 14 also shows PM 10 

## concentrations for comparison (where available). PM 2.5 

## accounts for more than half of the PM 10 

## levels in these areas.

■ 

## Los Angeles: PM 2.5 

## concentrations have decreased substantially since 1980. Although concentrations have leveled off in recent

### 17 **Figure 14. Comparison of historical PM 2.5**  

### and PM **10** 

### annual average concentrations, 1979–2003.

Concentration range ( μ g/m 3 )

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

### A

**verage Annual PM 2.5**  

### Concentrations, 1979–1983

Source: Inhalable Particulate Network

Concentration range ( μ g/m 3 )

≤ 15 [24 Cities] 15.1 - 20 [13 Cities] > 20 [2 Cities] 

### A

**verage Annual PM 2.5**  

### Concentrations, 2001–2003

Source: Federal Reference Method Network



## Note: The 1979–1983 data are from the Inhalable Particulate Network (IPN).The 1984–1999 data are from EPA’s Air Quality System.The 1999–2003 data are from the Federal Reference Method (FRM) network.The 1993–2003 data for W

ashington, DC, are from the IMPROVE network. 0 10 20 30 40 50

0 10 20 30 40 50

0 10 20 30 40 50 PM 2.5 PM 10 

### PM **2.5** 

### Annual Average Concentrations **Los Angeles, CA**

**W ashington, DC** 

**Chicago, IL**Concentration,μg/m3Concentration,μg/m3Concentration,μg/m3

79 81 83 85 87 89 91 93 95 97 99 01 03

Incomplete Data Incomplete Data

79 81 83 85 87 89 91 93 95 97 99 01 03

79 81 83 85 87 89 91 93 95 97 99 01 03 PM 2.5 NAAQS Level PM 2.5 NAAQS Level PM 2.5 NAAQS Level

PM 2.5 PM 10 PM 2.5 PM 10

### 18 **Episodic Events** 

## Rural Sulfate Trends In the eastern half of the United States, sulfates account for 25% to 55% of PM 2.5 

## annually. Power plants are the largest contributor to sulfate formation in the East, where they were responsible for more than 75% of sulfur dioxide emissions in 2003.In the East, power plants reduced sulfur dioxide emissions 33% between 1990 and 2003. As Figure 15 shows, this downward trend matches well with the trend in concentrations of rural sulfates (a 29% decrease). Because sulfates have such a large regional component (shown in Figure 6), these trends in sulfate concentration can also be used to help explain urban PM 2.5 

## trends. The reductions shown in Figure 15 are primarily attributable to implementation of EPA’s Acid Rain program. Phase I compliance began in 1995, affecting large coal-burning power plants in 21 eastern and midwestern states. Phase II implementation began in 2000, tightening emission limits on the Phase I power plants and setting restrictions on smaller coal-, oil-, and gas-fired plants. As the figure shows, sulfur dioxide emissions and sulfate concen trations decreased following implementation of both phases. A slight increase in SO 2 

## emissions in the latter half of the 1990s

w as likely due to power plants not affected until Phase II began in 2000. The small increase from 2002 to 2003

r esulted from increased electricity production by coalfired and oil-fired units. These units emit m uch more SO 2 

## than natural gas units that generated less power in 2003. This annual variation does not affect the total limit on SO 2 

## emissions under the Acid Rain Program. (For more information, see www.epa.gov/air/oap.html and www.epa.gov/acidrainreport/.)

15,000

10,000

5,000

0 90 91 92 93 94 95 96 97 98 99 00 01 03 02Yearly Emissions,Thousand Tons 6
5
4
3
2
1
0Sulfate Concentrations,μg/m3

Sulfate Concentrations SO 2 Emissions from Power Plants 

### Figure 15. Eastern annual trends of sulfur dioxide **emissions from power plants and sulfate concentrations. Satellite photo of forest fires, southern**  **California, October 27, 2003.** PM concentrations can increase dramatically due to human-caused or natural episodic events, such as biomass burning, meteorological inversions, dust storms, and volcanic and seismic activity. These events are rare, affecting less than 1% of reported PM 2.5 concentrations between 2001 and 2003. Episodic events can affect people’s short-term PM exposure, briefly pushing hourly and daily PM levels into the unhealthy ranges of the AirQuality Index. However, these events rarely have a significant effect on annual or longer averages of PM. Biomass burning can be either a human-initiated event, as in the burning of vegetation for land clearing or land use change, or a natural event, as in the wild fires resulting from lightning. Biomass burning can significantly increase PM 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 usually dominate the PM 2.5 concentration profile during these fire episodes. T

opography and meteorological conditions make some areas more susceptible to episodic events. In mountain regions, temperature inversions sometimes trap polluted air during the winter. Wintertime PM 2.5 and PM 10 can be more than three times higher than other seasonal averages. Woodstove smoke, containing large amounts



## Note: Sulfate concentrations are from EPA’s CASTNET monitoring network, www.epa.gov/castnet

### 19 **Dust storm, Phoenix, Arizona, August 19, 1999. T** 

**emperature inversion, Salt Lake Valley, Utah, January 13, 2004.**  of organic carbon, is often identified as a significant source of the elevated wintertime PM concentrations. Arid desert conditions in the southwestern United States make this region more vulnerable to wind-blown dust than other regions of the nation. Most dust events are caused by passage of weather fronts and troughs and downmixingof upper-level winds. Cyclone development and thunderstorms result in the most dramatic dust clouds with thelowest visibilities. Dust-related events are typically dominated by large, coarse particles, but fine particle levels also increase. The effects of dust storms can also be seen globally. Giant sand storms originating in the Sahara Desert can blow across the Atlantic to South America, the Caribbean, and the southeastern United States, transporting several hundred million tons of dust each year. Movement of dust from Africa has increased since 1970 because of an increase of dry weather in the Saharan region. Satellite pictures also confirm that sandstorms originating in China’s Gobi Desert occasionally cross the Pacific to the United States. T ransport from Africa typically occurs in the summer, and transport from Asia typically occurs in the spring.



### Satellite photo of giant cloud of dust originating **in North Africa moving westward.**

### 20 

## Note: Sulfate and nitrate concentrations from the CASTNET monitoring network were adjusted to represent mass in PM 2.5 

## and include ammonium as well as water.Trends for crustal were not available so constant values based on 2002–2003 data for each region were used. See www.epa.gov/airtrends/pm.html for further details. 

## concentrations in the eastern United States match

w ell 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 concentrations and power plant SO 2 

## emissions can vary among the subregions. Although trends in sulfate concentrations and SO 2 

## emissions match best

ov erall in the Southeast (SO 2 

## emissions down 15%, sulfate concentrations down 13%, from 1999 to 2003), the year-to-year comparisons for the Industrial Midwest and the Northeast do notshow such a close match. Sulfur dioxide emissions in the Industrial Midwest declined 19%, while sulfate concentrations declined 5%. In the Northeast, sulfur dioxide emissions were down 6%, and sulfate concentrations were up 3%. These subregional differences may be caused by several factors, the most important of which is likely to be transport. As Figure 17 shows, the ratio of sulfate concentrations to SO 2 

## emissions is higher in the Northeast than in the other

re g ions. This suggests that transport of emissions 

## PM **2.5** 

## Tr **ends in Three Regions (1999–2003)** 
To better understand ambient air quality, it is helpful to examine trends and the factors that contribute to those trends in specific regions. This section explores, in detail, trends in three regions in the eastern half of the country from 1999 to 2003. Figure 16 shows the 5-year regional trends in urban PM 2.5 

## and its major chemical constituents. In the Southeast, PM 2.5 

## declined sharply from 1999 to 2002, with little further change to 2003. Overall, the Southeast shows a 20% decrease in PM 2.5 

## from 1999 to 2003. In the Industrial Midwest, there is a gradual downward PM 2.5 

## trend from 1999 to 2001 and a more pronounced decrease from 2001 to 2003. Overall, PM 2.5 

## decreased 9% over the 5-year period. In the Northeast, PM 2.5 

## increased slightly from 1999 through 2001, then decreased through 2003, for an overall increase of 1%. Trends in PM components indicate that reductions in sulfatesappear to be responsible for approximately onethird of the reductions in PM 2.5 

## in the Industrial Midwest and the Southeast. Trends in sulfate 

# Explaining the Trends

**Figure 16. Trends in PM 2.5**  

### and its chemical constituents, 1999–2003.

**Industrial Midwest**Concentration,μg/m3

0 2 4 6 8 10 12 14 16

Y ear 1999 2000 2001 2002 2003

Crustal Nitrate PM 2.5

Sulfate

PM 2.5 Remainder (mostly carbon) 119 PM 2.5 Monitoring Sites

-9%

-5%

-17%

-4% **Southeast**Concentration,μg/m3

0 2 4 6 8 10 12 14 16

Y ear 1999 2000 2001 2002 2003

Crustal Nitrate PM 2.5

Sulfate

PM 2.5 Remainder (mostly carbon) 115 PM 2.5 Monitoring Sites

-20%

-13%

-32%

+18% **Northeast**Concentration,μg/m3

0 2 4 6 8 10 12 14 16

Y ear 1999 2000 2001 2002 2003

Crustal Nitrate PM 2.5

Sulfate

PM 2.5 Remainder (mostly carbon) 56 PM 2.5 Monitoring Sites

+1%

+3%

0%

+2%

### 21 

## Effect of Meteorology
W eather plays a role both in the atmospheric formation of PM 2.5 

## and in the quantity of emissions that contribute to this pollution. For this

r eport, we examined the effect of meteorology on sulfates, which are a major component of PM 2.5 

## , especially in the eastern half of the United States. To assess the effect of meteorology on annual average sulfate concentrations, EPA has conducted a preliminary analysis, adjusting sulfate levels based on weather conditions. (The blue line in Figure 17 represents measured sulfateconcentrations; the red line represents the meteor ologically adjusted sulfate concentrations.) One of the main parameters driving these preliminary adjustments is temperature. In the eastern half of the United States, 1999, 2001, and 2003 were near-normal meteorological years, so only minimal adjustments to sulfate concentrations

we re needed. In 2000, however, a cool summer may well have caused sulfur dioxide emissions to be lower than average, resulting in lower amounts of sulfates in the air. Adjusting for weather in 2000 raised estimated sulfate levels in all three

re g ions to the level expected during a year with

av erage weather conditions. Conversely, the summer of 2002 in the eastern United States was one of the hottest in recent y ears. Sulfur dioxide emissions were higher that y ear, likely due (at least in part) to increaseddemand for electricity for cooling. The meteorological adjustment for 2002 reduces the amount of sulfates in all three regions to levels expected during a normal meteorological year. In two of the three regions, the variations in power plant SO 2 

## emissions (illustrated by the y ellow bars in Figure 17 ) generally correlate more closely with the meteorologically adjusted sulfates (the red line) than the unadjusted sulfates (the b lue line). In the Industrial Midwest, however, adjusting for weather causes the sulfate trend tomove farther away from the sulfur dioxide emission trend in 2002-2003. More refined meteorological analyses and emission inventories are necessary to fully understand these results. 90 91 92 93 94 95 96 97 98 99 00 01 02 03 0 1 2 3 4 5 6Sulfate Concentration,μg/m3

0 1 2 3 4 5 6 7 8 9Power plant SO2Emissions, Million Tons 

### Northeast

Year

90 91 92 93 94 95 96 97 98 99 00 01 02 03 0 1 2 3 4 5 6Sulfate Concentration,μg/m3

0 1 2 3 4 5 6 7 8 9Power plant SO2Emissions, Million Tons 

### Southeast

Year



### Industrial Midwest

90 91 92 93 94 95 96 97 98 99 00 01 02 03 0 1 2 3 4 5 6Sulfate Concentration,μg/m3

0 1 2 3 4 5 6 7 8 9Power plant SO2Emissions, Million Tons

SO 2 emissions from power plants CASTNET sulfate concentrations Meteorologically adjusted sulfate concentrations Year 

### Figure 17. Meteorologically adjusted sulfate **concentrations, 1999–2003.**



## from other regions contributes to sulfate formation in the Northeast. Other factors that may contribute to the subregional differences in thesetrends include variations in meteorological conditions that are important to sulfate formation and transport, contributions to the Northeast fromCanada, and subregional differences in the contrib utions of sources other than power plants.

### 22 

## The PM **2.5** 

## Remainder Figure 16 (page 20) also shows the estimated trend in the “PM 2.5 

## r emainder” for each of the three regions. The remainder is estimated by subtracting all known PM 2.5 

## components from the total PM 2.5 

## mass. Some uncertainties exist in our interpretations of these data; however, the PM 2.5 

## r emainder appears to consist mostly ofcarbon-containing particles. Some small contrib utions to the PM 2.5 

## r emainder trend shown in Figure 16 include

■ 

## Tr ends 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 EPA’s PM 2.5 

## F ederal Reference Method monitoring network during its first few years of operation. Despite the uncertainties, the reductions in the PM 2.5 

## r emainder for the Industrial Midwest and Southeast appear to be due, in large part, to

r eductions in emissions that contribute to the formation of carbon-containing particles. The

r elative importance of various man-made emissions sources to these trends is uncertain and may

va ry by re g ion and urban area. Important sources of carbon-containing particles in urban air include direct emissions from sources such as motor vehicles, fuel combustion, and fires and atmospheric transformation of certain organic gases, including both regional biogenic emissions and some components of man-made VOCs. It is interesting to note that, in Figure 18, the decrease in the estimated PM 2.5 

## r emainder corresponds either to reductions in directly emitted fine particles or reductions in man-made VOC emissions. The Northeast region, however, shows virtually no net change in PM 2.5 

## or in any of its estimated components. Yet both direct PM 2.5 

## emissions and VOC emissions decreased from 1999 to 2003. EPA is continuing to conduct

r esearch and analysis to better identify and quantify key direct emission sources in addition to the relative contribution of man-made VOCemissions to atmospheric formation of carboncontaining particles. **Figure 18. PM 2.5**  

### emission trends.

96 97 98 99 00 01 02 03 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000Yearly Emissions, Thousand Tons **SO 2**  **Emissions**

96 97 98 99 00 01 02 03 0 100 200 300 400 500 600Yearly Emissions, Thousand Tons **Direct PM 2.5**  **Emissions** 96 97 98 99 00 01 02 03 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000Yearly Emissions, Thousand Tons **NO x**  **Emissions**

96 97 98 99 00 01 02 03 0 100 200 300 400 500 600Yearly Emissions, Thousand Tons

Industrial Midwest Northeast Southeast **VOC Emissions**

Y

ear

SO 2 NO x PM 2.5 VOC Northeast Southeast Industrial Midwest 

### Percent Change in Emissions from 1999 to 2003

-12 -15 -9

-5 -5 -7 -15 -3 -9
-14 -10 -9

### 23 

## will be required to attain the National Ambient Air Quality Standards for fine particles. EPA’s proposed Clean Air Interstate Rule (proposed in December 2003) will help states meet those

r equirements by reducing SO 2 

## and NO

x 

## emissions in the eastern United States thus reducingparticle pollution transported across state boundaries. Another regulation, the Best Available Retrofit Technology (BART) program, will

r equire the older, existing power plants to control PM emissions with retrofit pollution control equipment. Also, national mobile source rules are in place to strengthen the emission requirements for virtually all types of mobile sources. Manylocalities also have pollution reduction requirements for diesel engine retrofits as well as sulfur limits in diesel and gasoline engines. F or more details on the PM 2.5 

## r emainder, see ww.epa.gov/airtrends/pm.html. For information on EPA’s monitoring networks, see www.epa.gov/ttn/amtic/. 

## Control Programs Many programs have been put in place to reduce levels of particulate matter. Table 1 lists the major emission control programs that have contributed to reductions in PM since 1995 and will continue to reduce PM in the future. These programs control direct PM emissions and/or the emissions that contribute to PM formation, such as SO 2 

## , NO

x 

## , and VOCs. The control programsconsist of a series of regulations that reduce emissions from many stationary and mobile source sectors. For example, beginning in 2008, states

**PM Precursors Direct PM**  **a SO**  **2 NO**  **x VOC Implementation**  **Program Sector Reductions Reductions Reductions Reductions Date** Clean Air Nonroad Mobile sources X X X 2004-2015 Diesel Rule Clean Air Interstate Rule Electric Utilities X X X 2010-2015 (proposed December 2003) Acid Rain Program Electric Utilities X X 1995-2010 NO x SIP Call Electric Utilities X X 2004 Regional Haze Rule/ Electric Utilities b X X X 2013-2015 Best Available Retrofit T echnology PM 2.5 Implementation c Stationary/Area/ X X X X 2008-2015 Mobile sources PM 10 SIPs Stationary/Area/ X X X X Ongoing (e.g., San Joaquin Valley) Mobile sources Maximum Achievable Stationary/Area X X 1996-2003 Control Technology (MACT) Standards d V arious Mobile X X X X Ongoing Source 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 (P SD).

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 mine rals and ores,

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

e Includes such programs as onroad diesel and gasoline engines, nonroad gasoline engines, Low Sulfur Diesel and Gasoline Fuel Lim its for

onroad and offroad engines, Motorcycles, Land-based recreational vehicles, and Marine diesel engines. **T able 1.**  A Selection of Emission Control Programs Contributing to PM Emission Reductions, 1995–2015

### 24 The most direct way to obtain surface concentration data for particles is from the routine measurements made at surface monitoring 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 influenced by polluted air approaching over water. In addition, pollution may be transported aloft, undetected by surface monitors, and then descend to influence air at the ground. New work being done through a collaborative partnership between EPA, the National Aeronautics and Space Administration (NASA), and the National Oceanic and Atmospheric Administration (NOAA) uses satellite observations to augment the surface network monitoring data with satellite data.The NASA MODIS (Moderate Resolution Imaging Spectroradiometer) instruments on board the EOS (Earth Observing System) satellites EOS-Terra and EOS-Aqua provide twice-daily measurements of aerosol optical depth (AOD), a measure of how much light airborne particles prevent from passing through a column of atmosphere. Scientists use these measurements to estimate the relative amount of aerosols suspended in the atmosphere. Initial research shows that MODIS-derived data are suitable for tracking air quality events on a regional scale and may be a good surrogate for estimating the intensity of surface PM 2.5 concentrations. More research and data are needed to help show how aerosol loads are distributed vertically in the atmosphere so that MODIS-derived AOD can be put into the proper context. For more information on the MODIS-derived AOD and PM 2.5 pollution events, go to the Cooperative Institute for Meteorological Satellite Studies/Space Science and Engineering Center at the University 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. The majority of the high AOD seen in the images (yellow-red) was the result of several very large wildfires in western North America from British Columbia to Oregon. MODIS-derived AOD tracked the movement of the plume, which eventually affected surface PM 2.5 concentrations throughout the midwestern United States. IDEA (Infusing satellite Data into Environmental Applications) is a partnership between EPA, NASA, and NOAA. These agencies are working to improve air quality assessment, management, and prediction by infusing satellite measurements from NASA into EPA and NOAA analyses for public benefit.

**1 2** 

**3 4**  

### Using Satellites to Track Particulate Matter

### 25 

## National and regional regulations will make major reductions in ambient PM 2.5 

## levels over the next 10 to 20 years. In particular, the proposed Clean Air Interstate Rule (CAIR) and the existing NO

x 

## SIP Call, will reduce SO 2 

## and NO

x 

## emissions from certain electric generating units and industrial boilers across the eastern half of the United States. Regulations to implement the ambient air quality standards for PM 2.5 

## will

r equire direct PM 2.5 

## and PM 2.5 

## precursor controls in nonattainment areas. New national mobile source regulations affecting heavy-duty diesel engines, highway vehicles, and other mobile sources will reduce emissions of NO

x 

## , direct PM 2.5 

## , SO 2 

## , and VOCs.EPA estimates that current and proposed regulations for stationary and mobile sources will cut SO 2 

## emissions by 6 million tons annually in 2015 from 2001 levels. NO

x 

## emissions will be cut 9 million tons annually in 2015 from 2001 levels. V OC emissions will drop by 3 million tons, and direct PM 2.5 

## emissions will be cut by 200,000 tons in 2015, compared to 2001 levels. Figure 19 shows anticipated emission reductions. Most of the SO 2 

## r eductions are associated with electric generating sources, while NO

x 

## and VOC reductions for mobile sources are associated with continuing improvements in onroad and nonroad

v ehicles. Models predicting the effect of these emission

r eductions on air quality show that all areas in the eastern United States will have lower PM 2.5 

## concentrations in 2015 relative to present-dayconditions. In most cases, the predicted improvement in PM 2.5 

## ranges from 10% to 20%. EPA estimates that the proposed CAIR combined with existing regulations will bring the majority of the counties in the East into attainment for the PM 2.5 

## standards. As Figure 20 shows, 99 eastern counties are estimated to have exceeded the annual PM 2.5 

## standard in the 1999–2002 period, b ut only 13 of those counties are projected to exceed the PM 2.5 

## standard by 2015. More information on CAIR can be found at: www.epa.gov/interstateairquality/. 0 5 10 15 20 25

2001 2015 Direct PM 2.5 SO 2 NO x VOCTons (millions) 

### 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 Clean**

**Air Interstate Rule as proposed in December 2003.**

**Ambient PM 2.5**  

### , 1999–2002 **99 Counties Exceeding PM 2.5**  

### Standards

**Estimated PM 2.5**  

### , 2015 **13 Counties Exceeding PM 2.5**  

### Standards 

# The Future

### 26 

## Upcoming PM **2.5** 

## Designations EPA designates areas as attaining or not attaining the National Ambient Air Quality Standards for fine particulate matter (PM 2.5 

## ). EPA designates an area as “nonattainment” if it has violated the annual or 24-hour national PM 2.5 

## standard (assessed overa 3-year period) or if it has contributed to a violation of one of the standards. Once designated, nonattainment areas must take actions to improve their PM 2.5 

## air quality on a certain timeline. Designations are a crucial first step in the efforts of states, tribes, and local governments to reduce harmful levels of fine particles. For more details on PM 2.5 

## designations, visit www.epa.gov/ pmdesignations. Note: Designations are based on 3 years of data, and the boundaries of defined nonattainment areas may differ from the county boundaries used in this report. 

## PM **2.5** 

## and Other Pollutants Areas that experience PM 2.5 

## concentrations that exceed the National Ambient Air QualityStandards can also have air quality problems associated 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 share similar precursors and similar chemical reactions once in the atmosphere.” For example, nitrogen

o xides, which contribute to PM 2.5 

## formation, are also a key ingredient in ground-level ozone.
P ollutants may also be emitted from the same types of sources. Industries that emit air toxics may also emit chemicals that contribute to ozone or PM formation. Data indicate that millions of people likely live in areas where particle pollution levels are elevated along with ozone and/or air toxics. EPA will continue to analyze this information as

we w ork to protect public health across the country.

### 27 

## For Further Information
We b Sites Additional technical information: www. epa.gov/airtrends/pm.html Air Quality Index (AQI): www.epa.gov/airnow Clean Air Interstate Rule: www.epa.gov/interstateairquality/ C ASTNET: www.epa.gov/castnet/ Emissions: www.epa.gov/ttn/chief/ EPA 1996 PM Criteria Document: www.epa.gov/ttn/naaqs EPA Monitoring Networks: www.epa.gov/ttn/amtic/ Health and Ecological Effects: www.epa.gov/air/urbanair/pm/index.html IMPROVE: vista.cira.colostate.edu/improve National 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.html Office of Transportation and Air Quality: www.epa.gov/otaq Online Air Quality Data: www.epa.gov/air/data/index.html PM Supersites: www.epa.gov/ttn/amtic/supersites.html and www.epa.gov/ttn/amtic/laprog.html PM 2.5 

## Designations: www.epa.gov/pmdesignations Report on Acid Rain: www.epa.gov/acidrainreport/ Satellite information: idea.ssec.wisc.edu Source apportionment: www.epa.gov/oar/oaqps/pm25/docs.html Visibility: www.epa.gov/airtrends/vis.html AO D aerosol optical depth AQ I Air Quality Index BA RT best available retrofit technology CA A Clean Air Act C AIR Clean Air Interstate Rule C ASTNET Clean Air Status and Trends Network EOS Earth Observing System EPA U.S. Environmental Protection Agency FRM Federal Reference Method HAP hazardous air pollutants IDEA Infusing satellite Data into Environmental Applications IMPROVE Interagency Monitoring of Protected Visual Environments IPN Inhalable Particulate Network km kilometer MACT maximum achievable control technology MODIS moderate resolution imaging spectroradiometer NAAQS National Ambient Air Quality Standards NASA National Aeronautics and Space Administration NOAA National Oceanic and Atmospheric Administration NO x o xides of nitrogen PM particulate matter PM 10 

## particulate matter 10 μm or less in size PM 2.5 

## particulate matter (fine) 2.5 μm or less in size PM 10–2.5 

## particulate matter (coarse) between 10 and 2.5 μm in size PSD prevention of significant deterioation RACM reasonably available control
measures RACT reasonably available control technology SIP State Implementation Plan SO 2 sulfur dioxide TCM total carbonaceous mass TSP total suspended particulate μg/m 3 

## micrograms per cubic meter μm micrometers VO C v olatile organic compound 

## Acronyms**United States Environmental Protection** **Agency**Office of Air Quality Planning and StandardsEmissions, Monitoring, and Analysis DivisionResearch Triangle Park, NCEPA Publication No. EPA 454-R-04-002