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Particle Pollution

Particle pollution, also called particulate matter or PM, 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. 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.

To reduce particle pollution, state and federal regulations target nitrogen oxides (NOx) and sulfur dioxide (SO2) emissions from power plants and industrial combustion sources. Additionally, mobile source control programs help reduce organic carbon and NOx emissions through low-emission vehicles and cleaner gasoline.

Particle Pollution Basics

Particle pollution includes fine particles with an aerodynamic diameter of 2.5 microns or less (PM2.5), inhalable coarse particles with an aerodynamic diameter of 2.5 to 10 microns or less (PM10) and total suspended particles (TSP) with an aerodynamic diameter of 100 microns or less. For a sense of scale, the average human hair is 70 microns in diameter. In Wisconsin, the DNR monitors inhalable coarse and fine particles.

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.

Total Suspended Particles (TSP)

Wisconsin has a TSP standard to help protect citizens from damage caused by these particles. There are several TSP monitors operated by industrial facilities and audited by DNR staff. Currently there are no areas in Wisconsin that are violating the standard.

Health Effects

Both 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 the most likely to be affected by particle pollution exposure. Even if you are healthy, you may experience temporary symptoms from exposure to elevated levels of particle pollution.

For more information about the health effects of particle pollution, refer to:

The DNR also has additional air outreach resources available.

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 and making lakes and streams more acidic. 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 particle pollution conditions and environmental effects, refer to the following resources.

Standards - NAAQS

Overview of Particle Pollution Standards

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 current national ambient standards for particle pollution are listed below.


  1. 2012 annual primary standard: 12µg/m3 (annual mean, averaged over three years)
  2. 2006 annual secondary standard: 15µg/m3 (annual mean, averaged over three years)
  3. 2006 24-hour primary and secondary standard: 35 µg/m3 (98th percentile, averaged over three years)


  1. 24-hour primary and secondary standard: 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].

Compliance and Nonattainment Areas

As of June 1, 2014, all counties in Wisconsin are attaining the National Ambient Air Quality Standards (NAAQS) for particle pollution.

The EPA is in the process of designating nonattainment areas for the 2012 annual PM2.5 standard. The State of Wisconsin submitted a letter to EPA [PDF exit DNR] recommending attainment status statewide, because recent air quality data shows that all counties are meeting the standard. For more information about the designation process, visit EPA's Area Designations for the 2012 Annual Fine Particle (PM2.5) Standard [exit DNR].

PM2.5 Redesignation

In April 2014, EPA redesignated a three-county area in southeastern Wisconsin (Milwaukee, Racine and Waukesha counties) as attaining the 2006 24-hour standard for fine particulate matter, or PM2.5. As a result of this action, all counties in Wisconsin now meet the National Ambient Air Quality Standards (NAAQS) for particle pollution.

The redesignation is the outcome of successful statewide and regional efforts to limit emissions of pollutants associated with PM2.5. For more information about air quality improvements statewide, see Wisconsin's air quality trends.

Links to official redesignation documents are provided below.

Redesignation Process

In 2009, the EPA determined that Milwaukee, Racine and Waukesha counties were not meeting the 2006 24-hour PM2.5 standard. Counties that do not meet a federal standard based on monitored values of the outside air receive a nonattainment designation that triggers increased pollution control requirements for businesses in the area, along with other efforts to reduce particle pollution levels. The nonattainment designation for the three-county area in Wisconsin was established in a final rule [PDF exit DNR] published on Nov. 13, 2009.

Nonattainment areas are given a target date to meet the standard. State plans are then prepared that include regulations for emission controls needed to reduce the air pollution and meet the standard. These plans are called attainment demonstration plans. 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.

In light 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 [PDF].

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

Control Strategies and Regulations

Wisconsin has a number of control programs designed to meet other Clean Air Act requirements that reduce pollutants that form fine particles. These programs include:

  • Wisconsin's acid rain program, which limits emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from power plants;
  • Reasonably Available Control Technology (RACT) for volatile organic compounds and NOx in southeastern Wisconsin, designed to address high ozone concentrations in the area; and
  • EPA's Clean Air Interstate Rule (CAIR) [exit DNR], which further limits SO2 and NOx from power plants. The State of Wisconsin implements the NOx requirements of this rule under ch. NR 432, Wis. Adm. Code [PDF exit DNR]. Note: The Clean Air Interstate Rule was replaced by the Cross-State Air Pollution Rule (CSAPR) [exit DNR], a federal program that has established state emission budgets for NOx and SO2 for 2015 and 2017.

Mobile Sources

There are several state and federal pollution-control programs aimed at mobile sources including both highway vehicles, such as cars, and off-road equipment, such as all-terrain vehicles (ATVs). The federal government also regulates the fuels these vehicles and other equipment use, with the goal of having cleaner-burning fuels that do not contribute as much air pollution. Regulations include motor vehicle emission standards, vehicle inspection and maintenance, the required use of reformulated gasoline, ultra-low sulfur diesel fuel, low sulfur gasoline and gasoline vapor-recovery programs.

For more information on mobile sources visit our Vehicles (mobile sources) page.

Voluntary Reduction Programs

In some areas, governments, businesses and partner organizations have developed local and regional voluntary programs to reduce air pollution.

Regional Haze – Round 1

Visibility Protection and Haze

Visibility is degraded when light is scattered by tiny particles in the air, which reduces the clarity and color of what we see. This is referred to as haze and often occurs when the air is humid. Haze degrades visibility in many American cities and scenic areas. Air pollutants that contribute to fine particle formation and haze come from a variety of natural and man-made sources.

The EPA's Regional Haze Rule calls for state and federal agencies to work together to improve visibility in 156 national parks and wilderness areas [exit DNR], including the Grand Canyon, Yosemite, the Great Smoky Mountains and Shenandoah. These parks and pristine areas are called Class I Areas.

The haze rule requires that states — in coordination with EPA, National Park Service, U.S. Fish & Wildlife Service,  U.S. Forest Service and other interested parties — develop and implement air quality protection plans to reduce the pollution that degrades visibility. The overall goal is to eliminate the manmade effects on visibility by 2064. Interim milestones were established to ensure that states are on track to meet the 2064 goal. State regional haze plans for the first implementation period (Round 1) covering the period from 2005 through 2018 were due in December 2007.

Visit EPA's Regional Haze Program to learn more about the haze rule.

Regional Planning

Because regional haze can originate from sources located across large geographic areas, the EPA has encouraged the states and tribes to address visibility degradation from a regional perspective. States and tribes coordinate under five regional air quality organizations.

Lake Michigan Air Directors Consortium

Wisconsin addresses regional haze in collaboration with other Midwestern states as a member of the Lake Michigan Air Directors Consortium. The primary objective of LADCO's regional haze initiative is to assess both visibility impairment in the Class I areas located in Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin, and the impact of emissions from these states on visibility impairment. Members of the initiative include the six states, tribes, federal land managers and the EPA.

For more information on the other four regional air quality organizations and their work on regional haze, please visit the following websites:

Wisconsin's Round 1 Regional Haze State Implementation Plan (SIP)

LADCO's assessment showed that Wisconsin's emission sources impact visibility in four of the 156 Class I areas — two areas in northern Michigan and two areas in northern Minnesota. Under the federal Regional Haze Rule, Wisconsin must submit to the EPA a State Implementation Plan (SIP) to demonstrate it is making sufficient efforts to help meet reasonable progress goals for visibility improvement at these four areas. The SIP describes Wisconsin's strategy for meeting the progress goals by 2018 for these four areas, with the eventual goal of achieving pristine visibility conditions by 2064. This strategy takes advantage of emissions reductions from various control programs and includes submission of a plan for the application of Best Available Retrofit Technology (BART) for specific emission sources.

The DNR proposed Regional Haze SIP requirements in July 2011 for public comment. The department received comments from Georgia Pacific, U.S. Forest Service, National Parks Service and the EPA, and joint comments from Sierra Club and the Midwest Environment Defense Center. The DNR responded to these comments and amended the Wisconsin Regional Haze SIP accordingly.

The following documents support Wisconsin's Regional Haze SIP. The SIP is divided into three parts: 1) Wisconsin Regional Haze SIP; 2) Wisconsin's Implementation of BART; and 3) Revisions to Wisconsin's State Implementation Plan for Protection of Visibility. The public comments received on the July 2011 proposed Regional Haze SIP are also included below.

Wisconsin submitted its Round 1 regional haze SIP for the first planning period from 2005 – 2018 on January 18, 2012. The EPA approved it on August 7, 2012 (77 FR 46952).

Wisconsin's Implementation of BART

  • Cover Letter [PDF] — Implementation of BART
  • Attachment 1 [PDF] — EPA SIP checklist
  • Attachment 2 [PDF] — Draft BART Technical Support Document for EGUs — Dated July 1, 2011
  • Attachment 3 [PDF] — Draft BART Technical Support Document for Non-EGUs — Dated July 1, 2011
  • Attachment 4 [PDF] — Final BART Determination and Summary of Changes from Draft Technical Support Documents
  • Attachment 5 [PDF] — BART Modeling for PCA-Tomahawk, Thilmany, and Wausau-Mosinee
  • Attachment 6 [PDF] — Draft Administrative Order (AO) for Georgia Pacific
    * To be finalized after proposed approval by the EPA
  • Attachment 7 [PDF] — Template for EGU BART Permit Revisions for Implementation of BART
    * To be finalized in EGU-specific permits after proposed approval by the EPA
  • Attachment 8 [PDF] — BART Analysis Submitted by Georgia Pacific
  • Attachment 9 [PDF] — Proof of Public Hearing on July 29, 2010 (Response to Public Comments Included in Attachment 3)
  • Attachment 10 [PDF] — Proof of Public Hearing on Sept. 13, 2011 and Summary/Response to Public Comments

Revisions to Wisconsin's State Implementation Plan for Protection of Visibility

  • Cover Letter [PDF] — BART Rule
  • Attachment 1 [PDF] — EPA SIP checklist
  • Attachment 2 [PDF] — Chapter NR 433, Wis. Adm. Code, as amended
  • Attachment 3 [PDF] — Section NR 484 (11m), Wis. Adm. Code
  • Attachment 4 [PDF] — Proof of public hearing, including public hearing notice, for BART rules adoption. Copy of legal notice from Feb. 9, 2007, Wisconsin State Journal
  • Attachment 5 [PDF] — Background for AM-04-06 and public comments received for BART rules adoption — summary and response
  • Attachment 6 [PDF] — Proof of public hearing, including public hearing notice, for BART rules revision. Copy of legal notice from March 22, 2010, Wisconsin State Journal
  • Attachment 7 [PDF] — Background for AM-06-09 and public comments received for BART rules revision — summary and response

Comments Received on July 2011 Regional Haze SIP

Improving Visibility

There are a number of efforts underway to help improve visibility in Class I areas. They include Best Available Retrofit Technology (BART) requirements, reasonable progress and regional haze consultation.

Best Available Retrofit Technology (BART)

Best Available Retrofit Technology affects certain large sources of NOx, SO2 or direct particle pollution. This technology relates only to sources that began operation between 1962 and 1977. The federal regional haze regulation requires that BART determination be based on an analysis of the best system of continuous emission control technology available, performed on a source-by-source basis taking into account the following criteria:

  • the costs of compliance;
  • the energy and non-air quality environmental impacts of compliance;
  • any pollution control equipment in use at the source; and
  • the remaining useful life of the source.

Wisconsin's BART rule establishes a procedure for determining requirements to control SO2, NOx and particle pollution emissions from sources subject to BART, which are mainly boilers at electric generating power plants and at pulp and paper facilities. However, please note that the electric generating power plants subject to BART do not need to install, operate and maintain BART for SO2 and NOx controls if they are subject to the SO2 and NOx trading programs that are part of the Clean Air Interstate Rule (CAIR).

Reasonable Progress

Wisconsin, like all other states, must develop a plan to address reasonable progress in all Class I areas where emissions from the state significantly contribute to visibility degradation. The purpose of reasonable progress is to ensure that continuing progress is being made toward the 2064 visibility goal. The reasonable progress plan must address five factors which should be considered in evaluating potential emission control measures to meet visibility goals:

  • cost of compliance;
  • time necessary for compliance;
  • energy and non-air quality environmental impacts of compliance;
  • remaining useful life of any existing source subject to such requirements; and
  • uniform rate of progress.

Regional Haze Consultation - Northern Class I Areas

Michigan and Minnesota, along with representatives of other states (including Wisconsin), tribal governments and federal agencies, are working to address visibility impairment due to regional haze in four northern Class I areas: Boundary Waters Canoe Area Wilderness, Voyageurs National Park, Isle Royale National Park and Seney National Wildlife Refuge.

To support consultation in the development of reasonable progress plans for the Northern Class I Areas, the interested parties created a technical document that addresses the causes of visibility degradation in the area. The key findings of the document are as follows:

  • The chemical species that affect visibility impairment include ammonium sulfate and, to a lesser degree, ammonium nitrate and organic carbon.
  • The pollutants and source sectors that contribute the most to visibility impairment include:
    • sulfur dioxide emissions from power plants/electrical generating units (EGUs) and certain non-EGUs, which lead to sulfate formation;
    • nitrogen oxide emissions from a variety of sources such as motor vehicles, which lead to nitrate formation;
    • ammonia emissions from livestock waste and fertilizer applications, which are also important, especially for nitrate formation; and
    • organic carbon concentrations, which are thought to be mostly secondary organic aerosols of biogenic origin and, on an occasional episodic basis, from fire activity.
  • The source states that contribute the most to visibility impairment are Michigan, Minnesota and Wisconsin. Other nearby states also contribute to visibility impairment.
  • Current visibility levels are well above natural conditions.

For more information, read LADCO's Regional Haze in the Upper Midwest: Summary of Technical Information [PDF exit DNR].

Minnesota "Ask"

Through the regional consultation process, the Minnesota Pollution Control Agency (MPCA) determined that Wisconsin significantly contributes to visibility impairment at Boundary Waters Canoe Area Wilderness and Voyageurs National Park. The MPCA asked the states that contribute to visibility impairment at those sites to consider the following control programs when developing their visibility plans.

  • Implementation of BART.
  • Matching statewide average emission rate for power plants to Minnesota's voluntary emission rates.
    • NOx – 0.25 lbs/mmBtu
    • SO2 – 0.25 lbs/mmBtu
  • Continued assessment of reasonable measures for industrial/commercial/institutional boilers, reciprocating engines and turbines.

For more information, see Minnesota's regional haze plan [exit DNR].

Vermont "Ask"

Through the regional consultation process with the Mid-Atlantic/Northeast Visibility Union (MANE-VU), Vermont determined that Wisconsin significantly contributes to visibility impairment at Lye Brook Wilderness. Vermont asked the states that contribute to visibility impairment at Lye Brook to consider the following control programs when developing their visibility plans.

  • Implementation of BART.
  • 90% SO2 reduction at selected power plants.
    • Pleasant Prairie is the only identified power plant in Wisconsin and has installed scrubbers to meet the 90% goal.
    • 28% SO2 reduction from non-power plant sources.
      • The 28% reduction is relative to 2018 on-the-books emission projections.

For more information on Vermont's regional haze plan, please see the Vermont regional haze plan.

Wisconsin's Regional Haze Progress Report

The federal Regional Haze Rule requires states to submit progress reports five years after they submit their initial regional haze SIPs. The progress report serves as an assessment of whether a state's regional haze SIP is being implemented appropriately and whether reasonable visibility improvement is being achieved. Wisconsin's five-year progress report shows that pollutant emissions from Wisconsin sources decreased and visibility conditions at Minnesota and Michigan Class I areas improved over the five-year period as expected. These considerations, in part, helped DNR determine that Wisconsin's regional haze SIP continued to support visibility improvement at nearby Class I areas. The EPA approved Wisconsin's five-year progress report in December 2017.

Regional Haze – Round 2

Round 2 of the Regional Haze Program

The federal Regional Haze Rule (or "Haze Rule") requires states to re-assess and revise their incremental regional haze State Implementation Plan (SIP) every 10 years to continue meeting reasonable progress goals for natural visibility conditions at Class I areas by 2064. The Haze Rule, originally adopted on July 1, 1999, was revised effective January 10, 2017 (82 FR 3078). Under the original rule, regional haze SIP revisions covering the second implementation period (Round 2) from 2018 through 2028 was due July 31, 2018; however, the U.S. Environmental Protection Agency (EPA) extended the deadline to July 31, 2021, in the 2017 amendments to the Regional Haze Rule.

Development of Wisconsin's Round 2 Regional Haze SIP

Wisconsin addresses regional haze in collaboration with other Midwestern states as a member of the Lake Michigan Air Directors Consortium (LADCO). The primary objective of LADCO's regional haze initiative is to assess both visibility impairment in the Class I areas located in Illinois, Indiana, Michigan, Minnesota, Ohio and Wisconsin, and the impact of emissions from these states on visibility impairment. For the Round 2 period, it was determined that emission sources in Wisconsin impact visibility at four nearby Class I areas:

  • Isle Royale National Park (Michigan);
  • Seney Wilderness Area (Michigan);
  • Boundary Waters Canoe Area (Minnesota); and
  • Voyageurs National Park (Minnesota).

Under the Haze Rule, a state contributing to visibility impairment of a Class I area in another state is required to consult with the affected state to develop coordinated emission management strategies containing the emission reductions necessary to make reasonable progress (40 CFR § 51.308(f)(2)(ii)). Wisconsin worked with Michigan, Minnesota and other LADCO states to develop a long-term strategy to ensure continued improvements in visibility conditions at the Class I areas that Wisconsin impacts. States must also engage Federal Land Managers (FLMs) and consider their input when developing their proposed regional haze SIP revisions (40 CFR § 51.308(i)).

Federal Land Manager Comments Received on February 2021 Preliminary Draft of Wisconsin's Round 2 Regional Haze SIP

Wisconsin shared its preliminary draft Round 2 haze SIP with FLMs on February 22, 2021, initiating a 60-day mandatory FLM review period (40 CFR § 51.308(i)(2)). The DNR received the following comments during the 60-day FLM review period.

Wisconsin's Round 2 Regional Haze SIP

Wisconsin submitted its Round 2 haze SIP for the second planning period from 2018-2028 on July 30, 2021.

Wisconsin Round 2 Haze SIP