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Air Pollutants and Standards

Good air quality is important to your health and the environment. There are many air pollutants that can directly affect your health through breathing, such as air toxics, asbestos, ground-level ozone and particulates. The specific pollutant, its concentration in the air, the length of time of exposure, your own health conditions and the environmental quality of the area are all factors in how air pollution affects your health. There are federal and state standards for six common air pollutants; hundreds of other air toxics are regulated through permits.

Carbon monoxide

Carbon monoxide (CO)

Carbon monoxide (CO) is a colorless, odorless and tasteless gas. It may temporarily accumulate at harmful levels, especially in calm weather during winter and early spring, when fuel combustion reaches a peak and carbon monoxide is the most stable due to the low temperatures.

Sources of carbon monoxide include:

  • automobile emissions, with high levels possible near large parking lots, traffic jams or crowded city streets where large numbers of slow-moving cars accumulate;
  • home/building heating;
  • volcanoes, thunderstorms and forest fires;
  • vegetation during various growth stages; and
  • the chemical transformation of methane, a gas emitted from decaying plants in swamps and marshlands.

Carbon monoxide from natural sources usually dissipates quickly over a large area, posing no threat to human health. The one-hour federal standard for carbon monoxide is 35 parts per million (ppm). All counties in Wisconsin meet this standard.

Please see EPA for more information about carbon monoxide [exit DNR].


State implementation plan for lead

The U.S. EPA revised the primary and secondary National Ambient Air Quality Standards (NAAQS) for lead on Oct. 15, 2008. The Clean Air Act require states to submit a state implementation plan (SIP) to provide for the implementation, maintenance and enforcement of a revised NAAQS within three years of promulgation of the revised standard.

The DNR has determined that the current SIP provisions are adequate to address the federal health standard for lead as required by the CAA.

Lead sources and federal standards

Lead (Pb) is the most abundant toxic heavy metal. Industrial sources of lead emissions include:

  • waste oil and solid waste incineration;
  • iron and steel production;
  • lead smelting; and
  • battery and lead alkyl manufacturing.

The major sources of lead emissions have historically been from fuels in cars and trucks and industrial sources. As a result of regulatory efforts to remove lead from gasoline, emissions of lead from the transportation sector dramatically declined by 95% between 1980 and 1999, and levels of lead in the air decreased by 94%  between 1980 and 1999. Today, the major sources of lead emissions are lead smelters, ore and metals processing facilities and piston-engine aircraft operating on leaded aviation gasoline.

The primary, health-based standard for lead is 0.15 micrograms per cubic liter (μg/m3). This standard is measured as total suspended particles (TSP) for a rolling three month average. The secondary, welfare-based standard for lead is identical to the primary standard. All counties in Wisconsin meet these standards.

On Dec. 14, 2010, the EPA revised the ambient monitoring requirements for measuring lead in the air. These amendments expand the nation's lead monitoring network to better assess compliance with the 2008 revised standard for lead.

See EPA for more lead information [exit DNR].

Nitrogen oxides

Nitrogen oxides (NOx)

Nitrogen gas, normally unreactive, comprises about 80% of the air. At high temperatures and under certain other conditions it can combine with oxygen in the air, forming several different gaseous compounds collectively called oxides of nitrogen (NOx). Nitric oxide (NO) and nitrogen dioxide (NO2,the criteria pollutant) are the two most important.

Major sources of nitrogen oxides include:

  • fuel combustion in power plants and automobiles; and
  • processes used in chemical plants.

The EPA first set standards for NO2 in 1971, setting both a primary health standard and a secondary public welfare standard at 53 parts per billion (ppb) annually. The agency has reviewed the standards twice since that time, but chose not to revise the standards. All areas in the U.S. currently meet NO2 standards.

The last review of the NO2 primary standard was completed in 2010. At that time, EPA established a new one hour NO2 standard at the level of 100 ppb and retained the annual average NO2 standard of 53 ppb. All counties in Wisconsin meet the annual standard and monitoring for the one-hour standard is under development.

See EPA for more information on NO2 [exit DNR].

Important NO2 documents

Sulfur dioxide

Sulfur dioxide (SO2)

Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as "oxides of sulfur." The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for criteria pollutants, including sulfur dioxide. The largest sources of SO2 emissions nationally are fossil fuel combustion at power plants (73%) and other industrial facilities (20%).

The first SO2 air quality standards were set in 1971, including a 24-hour average primary standard at 140 ppb, an annual average primary health standard at 30 ppb and a three-hour, secondary public welfare standard of 500 ppb.

Recent changes

In 2010, the EPA revised the SO2 standard by establishing a new one-hour average primary standard at 75 ppb. The most recent SO2 health information suggests that the majority of SO2-related health risks are associated with short-term exposures. As part of this action, EPA revoked the other two primary standards. The three-hour average secondary standard is currently under review.

Health effects of SO2 pollution

Current scientific evidence links short-term exposures to SO2 – ranging from five minutes to 24 hours – with an array of adverse respiratory effects, including bronchoconstriction and increased asthma symptoms. These effects are particularly important for asthmatics while exercising or playing.

Studies also show a connection between short-term exposure and increased visits to emergency care and hospital facilities for respiratory illnesses, particularly in at-risk populations including children, the elderly and asthmatics.

2010 SO2 NAAQS implementation

Please visit SO2 NAAQS implementation for information on implementing the new standard.

Important SO2 documents



Particle pollution (also called particulate matter or PM) is solid particles or liquid droplets suspended in the air. 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, the 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 such low-emission vehicles and cleaner gasoline help reduce Volatile Organic Compounds (VOC) and NOx emissions from mobile sources.

For more information, please visit Particles.

Important particulate matter documents




Ozone is a gas that occurs in both Earth's upper atmosphere and at ground level. When ozone is at ground level, it is a major component of smog and can cause a number of health problems for humans and other living things. Because of this serious health risk, the DNR monitors ground-level ozone around the state and issues air quality advisories when levels become potentially harmful. Counties that do not meet federal clean air standards for ozone require businesses and residents in those areas to take special measures to reduce ground-level ozone.

See Ozone for more information.

Important ozone documents