Air toxics in Minnesota

Air toxics are a group of pollutants that cause or may cause cancer or other serious health effects or adverse environmental and ecological effects. Air toxics are also known as Hazardous Air Pollutants (HAPs) which are specified in the Clean Air Act Amendments.

Health and ecological effects

People exposed to emissions of air toxic pollutants at sufficient concentrations and durations may have an increased chance of developing cancer or experiencing other serious health effects. These health effects can include damage to the immune system, as well as neurological, reproductive (e.g., reduced fertility), developmental, respiratory, and other health problems.

Unlike some more common pollutants, the federal government does not have standards for air toxics. Instead, MPCA uses risk guidelines called health benchmarks to assess the health risks associated with air toxics concentrations. These values are set at levels that would protect people who are most vulnerable to the potentially harmful effects of a contaminant.

In addition to exposure from breathing air toxics, some toxic air pollutants such as mercury can deposit onto soil or surface waters, from where they are taken up by plants and other aquatic life. These in turn are ingested by other animals and are eventually magnified up through the food chain. Like humans, animals may also experience health problems if exposed to sufficient quantities of air toxics over time.

Key air toxics of concern

The MPCA uses health benchmarks to assess the health risks associated with the concentrations of pollutants in the air. Monitoring and modeling data have identified three types of air toxics which are particularly important for Minnesota.

Volatile organic compounds (VOCs)

VOCs are emitted from many industrial and commercial processes as well as many of our daily activities. You may recognize them as the solvent-like fumes coming from paint, solvents, adhesives, gasoline, cleaning products, or other chemicals used in everyday activities. They are also released when fuels are burned in cars, trucks, generators, lawn mowers, machinery, and recreational equipment. Formaldehyde is an example of a VOC that is frequently found above health benchmark levels in urban areas such as the Twin Cities.


Metals are naturally occurring elements that are emitted from many industrial processes and as a byproduct of fossil fuel combustion. Metals such as chromium, arsenic and nickel are sometimes found above health benchmarks in areas where large amounts of particles are emitted.

Polycyclic aromatic hydrocarbons (PAHs)

PAHs are a class of more than 100 chemicals made of complex combinations of carbon and hydrogen atoms. PAHs come from sources like tobacco smoke, wood smoke, vehicles, asphalt roads, or smoke from prescribed burning.

Air toxics monitoring

The MPCA measures the amount of many toxic pollutants in the air. Air toxics monitoring focuses on volatile organic compounds (VOCs) and metals. The MPCA also monitors other air toxics, such as PAHs, as part of special studies.

Air monitoring measures air pollution concentrations at fixed locations in the Twin Cities Metropolitan Area and in Duluth. Air toxics monitoring results are compared to state and federal health benchmarks. Additional information about MPCA air toxics monitoring can be found at Air pollution monitoring and modeling. Air toxics monitoring results can be found in the Air toxics data explorer.

Sources of air toxics pollutants

The MPCA collects and reports on emissions of air toxics from major sources in Minnesota every three years. These emissions are reported in the Minnesota Air Toxics Emissions Inventory. In 2014, the majority of air toxics were released from off- and on- road vehicles as well as smaller non-permitted sources. However, sources of individual air toxic pollutants can be very different.

See Emissions data for statewide and facility emissions in Minnesota.

Air toxics modeling

Air modeling provides computer-modeled estimates of pollutant concentrations and risks across Minnesota. Air modeling incorporates air pollution emissions data, facility characteristics and meteorological data to predict air pollutant concentrations. The MPCA uses air modeling to support air permitting, to assess health risks associated with air toxics emissions in Minnesota, and to prioritize emission reduction activities.

More information about air toxics modeling programs can be found at MPCA's Air modeling and human health.

Risk assessment

Risk assessment is a way of estimating the potential for negative health effects from air pollution. Minnesota does not have standards for air toxics. Instead, MPCA uses risk guidelines called health benchmarks to assess the health risks associated with air toxics concentrations. A benchmark is a level below which a pollutant is unlikely to cause adverse health effects in sensitive populations. The inhalation health benchmarks MPCA uses for risk assessment are available below.

Potential health effects from air toxics are considered using the air emissions risk analysis (AERA) process. These are also incorporated into the regulatory and environmental decision making framework.

Additionally, since the MPCA only monitors for air toxics at a few sites in the Twin Cities and Duluth, the MPCA uses emissions and modeling data to estimate the concentrations of air toxics across Minnesota. These concentrations are then used to estimate health risks using a tool called MNRISKS. MNRISKS is a computer model used to understand cumulative air pollution and health impacts in Minnesota. The model evaluates air pollution from both permitted and non-permitted sources. More information about MNRISKS and health risk model results can be found at Air modeling and human health.

What we’re doing to address air toxics

The MPCA works in many ways to protect and improve Minnesota’s air quality. Visit What we’re doing to improve air quality for more information.

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