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Change in the air

For 50 years, the Clean Air Act has delivered steady and remarkable improvements

Craig Czarnecki and Lindsay Haas

wide-open space with blue skyTHOMAS MEYERWisconsin has the Clean Air Act to thank for ensuring fresh, clean air at spaces such as Black Earth Rettenmund Prairie State Natural Area.

Step outside today and take a breath. This is some of the cleanest air Wisconsin has had in decades.

A landmark piece of environmental legislation passed 50 years ago, the Clean Air Act, is largely responsible for the quality of the air we breathe today. Considered to be one of the more successful and comprehensive of all federal laws, the Clean Air Act set in motion an extensive series of successful environmental protection programs that continue to benefit citizens today.

The early 20th century was marked by a series of air pollution events that escalated as new technologies led to greater electricity consumption, increased industrial production and a more automobile-based society. Following extensive public concerns regarding air pollution throughout the 1960s — and concurrent with the growth of the environmental movement — in 1970, Congress passed the Clean Air Act.

This law, along with significant amendments to the act passed in 1990, put into place a wide range of state and federal regulatory programs to improve the quality of the nation’s air.

This included setting national health-based standards for air quality, establishing air permitting requirements, authorizing regulations to limit air pollutant emissions from industrial facilities and motorized vehicles, and ensuring protection of visibility.

Many actions we take for granted today, such as cleaner-burning vehicles and pollution controls on power plants, are thanks to the Clean Air Act.


aerial view of hazy sky over city of MilwaukeeDNR FILESThe haze of air pollution hangs over Milwaukee's skyline, seen from an airplane circa 1980.

Since the passage of the Clean Air Act, the combined emissions of six common pollutants referred to in the act as criteria pollutants have dropped by 74% across the United States. Those are: particulate matter, sulfur dioxide, nitrogen oxides, volatile organic compounds, carbon monoxide and lead.

Emissions of mercury and other toxic pollutants also have dropped substantially. These improvements occurred while the U.S. population and energy use increased, the economy continued to grow and Americans drove more miles than ever before.

These changes had a major impact on the overall health of people across the country. According to the U.S. Environmental Protection Agency, from 1970 to 2020, the Clean Air Act prevented more than 435,000 premature deaths and prevented millions of cases of disease and sicknesses. Overall, the health benefits of the Clean Air Act have outweighed its costs by more than 30 to 1.

Although national in its impact, the Clean Air Act has undeniably helped improve the air quality in Wisconsin. To take just a few examples:

  • Emissions of air pollutants have significantly decreased. Due to acid rain controls and other programs, for example, emissions of sulfur dioxide from power plants and industry have decreased by 90% since 1999. Efforts to control emissions from mobile sources like cars and trucks, as well as large industrial facilities and power plants, reduced emissions of the two compounds that form ozone — oxides of nitrogen (NOx) and volatile organic compounds (VOCs) — by 50% in just the 12 years since 2002. Particulate matter emissions from industrial operations, combustion sources and open burning also have decreased over the last few decades.
  • Vehicles are polluting less. EPA initiatives to reduce air pollution from heavy-duty trucks and passenger vehicles have greatly reduced emissions from highway vehicles. Carbon monoxide, NOx, and VOC emissions in Wisconsin decreased significantly from 1970 to 2018 due to new vehicle standards — despite a doubling in the number of miles Wisconsinites traveled during that time.
  • More people are breathing healthy air. The portion of the state exceeding federal air quality standards has shrunk over the years, even as the standards themselves have become increasingly stringent. In the early 1980s, more than half of Wisconsinites lived in an area violating at least one air quality standard. Now, about 94% of the state population lives in areas that meet all air quality standards.



clear blue sky over Milwaukee skylineZOE SPROUTActions taken since passage of the Clean Air Act have resulted in reduced pollution and improved air quality in Milwaukee today.

Over the past 50 years, the Clean Air Act has dramatically improved air quality and human health throughout the state, yet there is still much to accomplish. The coming years will see the DNR turn to the Clean Air Act to address challenges both old and new, including:

  • Responding to climate change. The response to this challenge is one of the defining issues for this generation. Reducing greenhouse gas emissions, moving toward a cleaner automotive fleet and encouraging more efficient use of energy are just some of the ways the act will be used to help address human impact on the climate. At the state level, Gov. Tony Evers has signed a pair of executive orders to address climate change. Executive Order #52 has created the Governor’s Task Force on Climate Change, while Executive Order #38 aims to have Wisconsin utilities carbon-free by 2050.
  • Addressing PFAS. Per- and polyfluoroalkyl substances (PFAS) are a large group of human-made chemicals used in industry and consumer products worldwide since the 1950s. Exposure to certain PFAS may increase the risk of adverse health effects, such as thyroid disease, low birth weights and cancer. PFAS can be emitted into the air as vapors or fine particles, but there are currently no federally approved sampling methods for PFAS compounds in ambient air. Understanding how PFAS reacts and moves in the air, determining where and how PFAS is emitted, and developing strategies to address the issue all pose new challenges.
  • Solving lakeshore ozone challenges.  While ozone levels across the state have decreased dramatically over the last few decades, some areas along Wisconsin’s Lake Michigan shoreline continue to experience ozone levels above federal standards. Determining how and where to reduce regional ozone-causing emissions further, and from which sources, is an ongoing challenge. Understanding more about the science of ozone formation and transport in the region will help.

The Clean Air Act has been a resounding success for 50 years. As a result, Wisconsin residents are fortunate to breathe air every day that is clean to a degree once unimaginable.

In the decades to come, the DNR will continue to rely on this landmark piece of legislation to ensure that future generations of Wisconsinites have access to clean, healthy air.

Craig Czarnecki and Lindsay Haas are members of the DNR Air Program Outreach Team.



Here’s a look at actions involving air quality in Wisconsin in the past 50 years.

  • 1970 Clean Air Act is passed, laying the groundwork for decades of comprehensive public health and air quality improvements.
  • 1973 Phase-out of lead gasoline begins. By 1995, lead is banned from gasoline in all on-road vehicles, leading to a significant drop of lead levels recorded in human blood.
  • 1975 Energy Policy and Conservation Act sets fuel economy standards, prompting innovations for fuel efficient vehicles including the catalytic converter.
  • 1977 Clean Air Act amendments add major source permitting programs and offset trading policy.
  • 1978 U.S. bans chlorofluorocarbons in aerosol cans. CFCs are further phased out by the 1987 Montreal Protocol and 1990 Clean Air Act amendments. As of 1996, the U.S. no longer produces or imports CFCs due to their destructive effects on the Earth’s protective ozone layer.
  • 1986 Wisconsin’s Acid Rain law leads the nation, requiring electric utilities to reduce sulfur dioxide emissions.
  • 1987 The first Lake Michigan Ozone Study involves the DNR and partners to better understand lakeshore ozone issues (also 1995, 1999 and 2001).
  • 1988 Wisconsin again sets a national example with its Air Toxics Rule, limiting emissions of 438 hazardous air pollutants.
  • 1990 Federal Clean Air Act amendments are enacted, modernizing the original act and especially targeting urban smog, leaded gasoline, CFCs, acid rain and air toxics.
  • 1996 Major voluntary initiatives begin to reduce air pollution, including a DNR partnership called the Wisconsin Partners for Clean Air in Southeastern Wisconsin.
  • 2004 Wisconsin’s Mercury Rule requires large, coal-fired electric utilities to reduce toxic mercury emissions. A 2008 revision to the rule facilitates even larger emission reductions applied to facilities of all sizes.
  • 2007 U.S. Supreme Court decides that greenhouse gases are air pollutants under the Clean Air Act.
  • 2009 The DNR Air Program launches Air, Air Everywhere Poetry contest.
  • 2012 New passenger vehicles must comply with EPA’s first-ever national greenhouse gas emissions standards.
  • 2013 The DNR Air Program releases its first Air Quality Trends report.
  • 2017 Lake Michigan Ozone Study with the DNR and partners aims to understand the western Lake Michigan shoreline ozone chemistry.
  • 2018 Enhanced Ozone Monitoring begins, as required by federal rule, to better understand Wisconsin’s unique lakeshore ozone chemistry. This includes the DNR’s Mobile Air Monitoring Lab at lakeshore sites.
  • 2019 Gov. Tony Evers signs Executive Order #38, creating the Office of Sustainability and Clean Energy, and Executive Order #52, establishing the Governor’s Task Force on Climate Change. Both relate to efforts seeking to ensure clean air in Wisconsin.
  • 2020 The DNR celebrates 50 years of clean air in Wisconsin.