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Fine Particle (PM2.5) Designations

Frequent Questions

Answers to the following questions can be found by scrolling down or by clicking on the question of interest. If you need further information, please use the contact information provided.

What is PM2.5?

Where does PM2.5 come from?

Who is most at risk?

How can I find out about PM2.5 levels in my community?

What does nonattainment mean?

What does designation mean?

What will my area need to do to improve air quality if it is designated nonattainment for PM2.5?

What information does EPA use to determine whether an area should be a "nonattainment area?"

How can I participate in the designation process?

What is EPA doing to reduce PM2.5 levels?

What is the litigation history of the PM2.5 standards?

Where can I go for further information?


What is PM2.5?

Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke. Others are so small that individually they can only be detected with an electron microscope.

Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes.

Particles less than 10 micrometers in diameter (PM10) pose a health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), fine particles can lodge deeply into the lungs.

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Where does PM2.5 come from?

Sources of fine particles include all types of combustion activities (motor vehicles, power plants, wood burning, etc.) and certain industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse." Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads. Other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes.

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Who is most at risk?

Roughly one out of every three people in the United States is at a higher risk of experiencing PM2.5 related health effects. One group at high risk is active children because they often spend a lot of time playing outdoors and their bodies are still developing. In addition, oftentimes the elderly population are at risk. People of all ages who are active outdoors are at increased risk because, during physical activity, PM2.5 penetrates deeper into the parts of the lungs that are more vulnerable to injury.

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How can I find out about PM2.5 levels in my community?

Air quality forecasts are often given with weather forecasts on local television and radio stations, and may be found on the weather page of your newspaper. Another way to learn about unhealthy exposures is to check daily Air Quality Index forecasts. Visit www.airnow.gov to find the forecast for an area near you.

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What does nonattainment mean?

The Clean Air Act identifies six common air pollutants that are found all over the United States. These pollutants can injure health, harm the environment and cause property damage. EPA calls these pollutants criteria air pollutants because the agency has developed health-based criteria (science-based guidelines) as the basis for setting permissible levels in the air we breath. PM2.5 is a criteria pollutant. EPA establishes national ambient air quality standards for each of the criteria pollutants. These standards apply to the concentration of a pollutant in outdoor air. If the air quality in a geographic area meets or is cleaner than the national standard, it is called an attainment area; areas that don't meet the national standard are called nonattainment areas.

In order to improve air quality in a nonattainment area, states must draft a plan known as a state implementation plan (SIP). The plan outlines the measures that the state will take in order to improve air quality. Once a nonattainment area meets the standards and additional redesignation requirements in the Clean Air Act [Section 107(d)(3)(E)], EPA will designate the area to attainment as a "maintenance area."

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What does designation mean?

States and tribes submit recommendations to the EPA as to whether or not an area is attaining the national ambient air quality standards for a criteria pollutant. The states and tribes base these recommendations on air quality data collected from monitors at locations in urban and rural settings. After working with the states and tribes and considering the information from air quality monitors, EPA will then "designate" an area as attainment or nonattainment for the PM2.5 standard. If an area is designated as nonattainment it signifies to the public that the air in the area is unhealthy to breathe.

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What will my area need to do to improve air quality if it is designated nonattainment for PM2.5?

States with designated nonattainment areas are required under the Clean Air Act to develop a State Implementation Plan and submit it to EPA within three years (around April 2008). (Tribes may elect to develop tribal implementation plans but are not required to do so.) This plan must include enforceable measures for reducing air pollutant emissions leading to the formation of fine particles in the atmosphere. The plan must also provide steps for the area to attain the PM2.5 standards as quickly as possible, and the area must show how it will make reasonable progress toward attaining the standards.

In assessing how quickly an area can attain the standards, states should consider the air quality improvements that can be achieved from a combination of national, state, and local measures. For example, states should take into account existing emission reduction programs (e.g. national emission standards for cars and trucks; and the Clean Air Interstate Rule to reduce powerpolant emissions; or local efforts such as diesel engine retrofit programs), plus any new programs or regulations that can be implemented within the state or local nonattainment area.

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What information does EPA use to determine whether an area should be a "nonattainment area?"

The Clean Air Act defines a nonattainment area as the area that is violating the national ambient air quality standard OR a nearby area that is contributing to a violation of the PM2.5 standards. The PM2.5 standards are based on averaging air quality measurements both annually and on a 24 hour basis. The annual standard for PM2.5 is met whenever the 3 year average of the annual mean PM2.5 concentrations for designated monitoring sites in an area is less than or equal to 15.0 µg/m3. The 24 hour standard for PM2.5 is met whenever the 3 year average of the annual 98th percentile of values at designated monitoring sites in an area is less than or equal to 35 µg/m3.

In addition to air quality data, EPA guidance on the PM2.5 designations process also discusses other important factors, including emissions of pollutants that lead to PM2.5 formation, population, commuting patterns, and expected growth, that states should evaluate in order to determine whether a county is a likely contributor to the area’s air quality problem.

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How can I participate in the designation process?

You can follow the designation process for the PM2.5 standard in your state by contacting your state environmental agency, attending public hearings related to the designations process in your area, and keeping informed about the current status of the designations process from this Web site and state Web sites. Information such as the latest list of counties having violating monitors for PM2.5, and technical data to be considered in designating nonattainment areas, can be found at the PM2.5 Designations Technical Information Page

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What is EPA doing to reduce PM2.5 levels?

EPA has a number of programs already in place that will help reduce emissions from power plants, cars, and other sources of emissions that lead to the formation of fine particles. More information on these programs can be found on the following sites:

Programs in Place

- Efforts to Reduce PM - General overview.

- Tier II standards for passenger cars and light trucks - Finalized February 2000.

- NOx SIP Call - Regional strategy to reduce nitrogen oxides from eastern states.  Primarily designed to meet the ozone NAAQS, but will provide some benefits in terms of reduced levels of nitrate fine particles.

- Diesel Engine Retrofit Programs - Voluntary programs to reduce diesel engine emissions.

- Clean Air Nonroad Diesel Emissions Rule - a comprehensive national program requiring stringent emissions controls on diesel engines used in construction, agriculture, and mining and significantly reducing the sulfur content of diesel fuel.

- Clean Air Interstate Rule - Permanently caps powerplant emission of particle forming sulfur dioxide (SO2) and nitrogen oxides (NOx) in the eastern US.

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What is the litigation history of the 1997 PM2.5 standards?

After EPA promulgated the PM2.5 and 8-hour ozone standards in July 1997, several industry organizations and state governments challenged EPA's action in the U.S. Court of Appeals for the District of Columbia Circuit (the D.C. Circuit). On May 14, 1999, the three-judge panel of the D.C. Circuit held in a split decision that the Clean Air Act, as applied by EPA in setting the 1997 standards for PM and ozone, was unconstitutional as an improper delegation of legislative authority to EPA. The ruling did not question the science or decision-making process used to establish the standards. The Court remanded the PM2.5 standards to EPA but did not vacate them. In June 1999, the Department of Justice (DOJ) and EPA petitioned the Court for a rehearing en banc with the entire D.C. Circuit Court. On October 29, 1999, the Court denied the petition for rehearing.

The DOJ and EPA then filed a petition for certiorari with the United States Supreme Court in December 1999 to appeal the decision of the D.C. Circuit, and the Supreme Court issued its decision to hear the appeal in November 2000. The Supreme Court issued its decision on the merits of the appeal on February 27, 2001. In that decision, the Supreme Court held that EPA's approach to setting the National Ambient Air Quality Standards in accordance with the CAA did not constitute an unconstitutional delegation of authority. The Supreme Court unanimously affirmed the constitutionality of the CAA provision that authorizes the Agency to set national air quality standards, stating that this provision "fits comfortably within the scope of discretion permitted by our precedent." The Supreme Court also affirmed that the CAA requires EPA to set standards at levels necessary to protect the public health and welfare, without considering the economic costs of implementing the standards. The Supreme Court remanded several other issues back to the D.C. Circuit, including the issue of whether EPA acted arbitrarily and capriciously in establishing the specific levels of the standards.

The D.C. Circuit heard arguments in this remanded case in December 2001, and issued its decision on March 26, 2002. The D.C. Circuit found that the Agency had "engaged in reasoned decision making," rejecting the claim that the Agency had acted arbitrarily and capriciously in setting the levels of the standards. This last decision by the D.C. Circuit gave EPA a clear path to move forward with implementation of the PM2.5 standards.

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Where can I go for further information?

If you would like further information, please visit the Contact Us page.

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