Air Quality_Content Page_Particle Pollution

Particle Pollution

Particulate Matter (PM) pollution consists of solid particles or liquid droplets suspended in the air. Fine particles (PM2.5) may be emitted directly into the atmosphere but are more commonly created by reactions of other pollutants, such as nitrogen oxides (NOx), sulfur dioxide (SO2), organic carbon and ammonia (NH3). Inhalable coarse particles (PM10) usually result from some type of mechanical action such as crushing or grinding, or from wind-blown dust. Exposure to these suspended particles and droplets can cause serious health problems in humans, especially those with respiratory conditions such as asthma and cardiac disease. The DNR's Air Management Program monitors particle pollution around the state and issues advisories when levels become potentially harmful.

Air quality has improved significantly in recent years, and PM levels in Wisconsin have decreased over the past few decades. Learn more about Wisconsin's air quality trends.

Basic Info

Particulate matter pollution includes fine particles with a diameter of 2.5 microns or less (PM2.5) and inhalable coarse particles with a diameter of 2.5 to 10 microns or less (PM10). For a sense of scale, the average human hair is 70 microns in diameter.

Fine Particles (PM2.5)

Sources of fine particle emissions include forest fires and wood stoves. Sources of the precursor pollutants that chemically react to form fine particles (NOx, SO2, organic carbon and ammonia) include power plants, industries and automobiles. Wind can carry these particles hundreds of miles from their sources. Fine particle levels typically peak in winter, but concentrations can also be high in summer.

Coarse Particles (PM10)

Sources of inhalable coarse particles include roadways and dusty industries. These particles are typically not transported great distances.

Health Effects

Inhalable coarse and fine particles pose health risks because they can bypass the body's natural defense mechanisms and affect both the lungs and heart. Scientific studies have linked particle pollution exposure to a variety of health problems, including:

  • increased coughing or difficulty breathing;
  • reduced lung capacity and function;
  • aggravated asthma;
  • chronic bronchitis;
  • irregular heartbeat;
  • nonfatal heart attacks and
  • premature death in people with heart or lung disease.

People with heart or lung diseases, children and older adults are most likely to be affected by particle pollution exposure. Even healthy people may experience temporary symptoms from exposure to elevated levels of particle pollution.

For more information about the health effects of particle pollution visit the EPA’s Particle Pollution Exposure webpage.

Environmental Effects

Particle pollution scatters light and is the major cause of reduced visibility in the United States. Many fine particles can also be acidic, causing acid rain. Deposition of nitrogen-containing particles may change the nutrient balance in lakes and rivers, affecting the diversity of ecosystems or damaging forests or crops. In addition, particle pollution can damage statues, monuments and buildings made of stone and other materials.

For more information on particle pollution conditions and environmental effects, visit the EPA’s Acid Rain webpage and Health Impacts of Particulate Matter webpage.

Air Quality Forecasts And Monitoring Data

Air Regulations

The federal Clean Air Act requires the U.S. Environmental Protection Agency (EPA) to develop two types of air quality standards for key air pollutants, including particulate matter.

  1. Primary standards — These standards protect public health, including the health of groups especially affected by air pollution, such as individuals with asthma or cardiac disease, children and the elderly.
  2. Secondary standards — These standards protect public welfare and the environment, including protection against damage to animals, crops and buildings.

These standards are referred to as National Ambient Air Quality Standards (NAAQS) and limit the amount of pollution in the air over certain time periods. The PM NAAQS are measured in 24-hour and annual increments. The table below outlines the current NAAQS for particulate matter. For more information on the National Ambient Air Quality Standards, visit EPA’s NAAQS webpage.

Pollutant Primary/Secondary Year Averaging Time Level Form
Particle Pollution PM2.5 Primary 2024 1 year 9 μg/m3 Annual mean, averaged over three years
Primary 2012 1 year 12 μg/m3 Annual mean, averaged over three years
Secondary 2006 1 year 15 μg/m3 Annual mean, averaged over three years
Primary and Secondary 2006 24-hours 35 μg/m3 98th percentile, averaged over three years
PM10 Primary and Secondary 1987 24-hours 150 μg/m3 Not to be exceeded more than once per year on average over three years

For more details see National Ambient Air Quality Standards [exit DNR].

2024 Standard

2024 Standard

Proposed Rule

On Jan. 27, 2023, the U.S. Environmental Protection Agency (EPA) published a proposed revision to the particulate matter (PM) National Ambient Air Quality Standard (NAAQS). The proposed rule would make the PM2.5 annual standard more stringent while retaining the 24-hour PM2.5 and PM10 standards. The table below shows the proposed standard range.

Standard Type Current Standard Proposed Standard Range
PM2.5 annual standard 12 µg/m³ (set in 2012) 9-10 µg/m³ (took comment on 8-11 µg/m³)
PM2.5 24-hour standard 35 µg/m³ (set in 2006) No change (took comment on 25-35 µg/m³)
PM10 24-hour standard 150 µg/m³ (set in 1987) No change

The DNR submitted comments on the proposed rule on March 28, 2023.

2024 Final Rule

On February 7, 2024, the U.S. Environmental Protection Agency (EPA) released a revised particulate matter (PM) National Ambient Air Quality Standard (NAAQS). The final rule, published in the Federal Register on March 6, 2024, makes the PM2.5 annual standard more stringent while retaining the 24-hour PM2.5 and PM10 standards. The rule is effective May 6, 2024. The table below shows the final standard.

Standard Type Previous Standard Final2024 PM NAAQS
PM2.5 annual standard 12 µg/m³ (set in 2012) 9 µg/m³
PM2.5 24-hour standard 35 µg/m³ (set in 2006) No change
PM10 24-hour standard 150 µg/m³ (set in 1987) No change

Earlier Standards

2012 PM Standard

On Jan. 15, 2012, EPA finalized the National Ambient Air Quality Standard (NAAQS) for PM. They lowered the annual PM2.5 standard to 12 µg/m³, the retained the 24-hour PM2.5 standard at 35 µg/m³ and retained the 24-hour PM10 standard at 150 µg/m³. The final rule and related technical documents are available on EPA’s 2012 National Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM).

Proposed Rule

Based on a review of the air quality criteria and the National Ambient Air Quality Standards (NAAQS), EPA proposed to make revisions to the primary and secondary NAAQS for PM to provide requisite protection of the public health and welfare.

The DNR submitted comments on this proposal on Aug. 31, 2012.

Area Designations

All areas of Wisconsin were designated as attainment for this standard.

2006 Standard

2006 PM Standard

On Oct. 17, 2006, EPA finalized the National Ambient Air Quality Standard (NAAQS) for PM. The EPA retained the annual PM2.5 standard to 15 µg/m³, lowered 24-hour PM2.5 standard to 35 µg/m³ and retained the 24-hour PM10 standard at 150 µg/m³. The final rule and related technical documents are available on EPA’s 2006 National Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM2.5).

Proposed Rule

Based on a review of the air quality criteria and the National Ambient Air Quality Standards (NAAQS), the EPA proposed to make revisions to the primary and secondary NAAQS for PM to provide requisite protection of the public health and welfare.

Area Designations

On Nov. 13, 2009, the EPA determined that Milwaukee, Racine and Waukesha counties were not meeting the 2006 24-hour PM2.5 standard. The nonattainment designation for the three-county area in Wisconsin was established in a final rule.

Area Redesignations

Nonattainment areas are given a target date to meet the standard. If at any time monitoring data show that air quality has improved and the county now meets the standard, the state can request the EPA to redesignate the county to attainment status.

In June 2012, the DNR submitted a request to the EPA to redesignate the three counties from nonattainment to attainment based on monitoring data collected between 2008 and 2011. The data showed that PM2.5 concentrations were no longer exceeding the levels of the standard. Measurements since 2011 continue to show attainment of the standard in the three-county area as well as the rest of the state.

As the result of a court decision (Natural Resources Defense Council v. EPA), the EPA requested that states, including Wisconsin, supplement their redesignation requests with additional information. The DNR submitted this information in the following document: Supplemental Information for a June 2012 Redesignation Request and Maintenance Plan for the 24-Hour Fine Particulate Matter National Ambient Air Quality Standard.

On Feb. 18, 2014, the EPA published a proposed rule to redesignate the three counties to attainment and approve all parts of Wisconsin’s maintenance plan. Comments were due to the EPA by March 20, 2014, and no adverse comments were received. On April 22, 2014, the EPA published its final approval of the redesignation.

1997 Standard

1997 PM Standard

On July 18, 1997, EPA finalized the National Ambient Air Quality Standard (NAAQS) for PM2.5. They put the annual PM2.5 standard at 15 µg/m³ and the 24-hour PM2.5 standard at 65 µg/m³ and retained the 24-hour PM10 standard at 150 µg/m³. The final rule is available in the Federal Register.

Proposed Rule

In accordance with sections 108 and 109 of the Clean Air Act (Act), the EPA reviewed the air quality criteria and national ambient air quality standards (NAAQS) for particulate matter (PM). Based on these reviews, the EPA proposed to change the standards for this pollutant.

Area Designations

All areas of Wisconsin were designated as attainment for this standard.