Key Findings for 2010-2012

Thanks to the Clean Air Act, the United States continues to make progress providing healthier air. The State of the Air 2014 shows that the nation’s air quality worsened in 2010-2012, but remains overall much cleaner than just a decade ago. More than 147.6 million people—47 percent of the nation—live where pollution levels are too often dangerous to breathe, an increase from last year's report. Despite that risk, some seek to weaken the Clean Air Act, the public health law that has driven the cuts in pollution since 1970.

The State of the Air 2014 report looks at levels of ozone and particle pollution found in official monitoring sites across the United States in 2010, 2011, and 2012. The report uses the most current quality-assured nationwide data available for these analyses.

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The report examines particle pollution (PM2.5) in two different ways: averaged year-round (annual average) and over short-term levels (24-hour). For both ozone and short-term particle pollution, the analysis uses a weighted average number of days that allows recognition of places with higher levels of pollution. For the year-round particle pollution rankings, the report uses averages calculated and reported by the U.S. Environmental Protection Agency (EPA). For comparison, the State of the Air 2013 report covered data from 2009, 2010, and 2011.1 More details about this process is in Methodology.

Overall Trends

Thanks to stronger standards for pollutants and for the sources of pollution, the United States has continued the long-term trends to lower ozone and particle pollution as well as other pollutants for decades. This figure from the EPA shows that, since 1970, the air has gotten cleaner while the population, the economy, energy use and miles driven increased greatly. Even as the economy continues to recover after the recession, overall air emissions that create the six most widespread pollutants continue to drop.

Source: U.S. EPA, Air Quality Trends, 2014
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In 2010-2012, many places made strong progress over 2009-2011 particularly in lower year-round levels of particle pollution. Thanks to reductions in emissions from coal-fired power plants and the transition to cleaner diesel fuels and engines, cleaner air shows up repeatedly in the monitoring data. Still, even with the cleaner air, the most-polluted cities failed to meet the official national limits, or standard, for year-round particle pollution.

Ozone was much worse in 2010-2012 compared to 2009-2011, likely due to warmer temperatures, especially in 2012. Fortunately, even these higher levels represent much better air quality compared to ten or 15 years ago. However, rising temperatures create conditions favorable to forming ozone. Communities will need more help to reduce ozone pollution in the warmer temperatures expected from the changing climate.

Sources of Pollution
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  • Ozone Pollution — More than 4 in 10 people lived in areas with unhealthful levels of ozone in 2010-2012. See which cities with the worst ozone had even more unhealthy air days.
  • Year-round Particle Pollution — More than 46.2 million people live in an area burdened year-round by unhealthful levels of deadly particle pollution. See which cities saw continued progress in cleaning up sources and which suffered even more pollution.
  • Short-term Particle Pollution — Many cities endured more days where particle pollution spiked during this period. Fourteen percent (14%) of people in the United States live where they suffered too many days with unhealthful levels of particle pollution.
  • Cleanest Cities — Only four cities made the cleanest list in all three categories, but several were among the cleanest in two.
  • People at Risk — Nearly half of the people in the U.S. live in counties that have unhealthful levels of either ozone or particle pollution. Learn more about people who face the greatest risk—probably someone you know is one of them.
  • What Needs to be Done to Get Healthy Air— What do we need to do as a nation? How can you help clean up the air?

1A complete discussion of the sources of data and the methodology is included in Methodology.

FACT: People who work or exercise outside face increased risk from the effects of air pollution.

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