Key Findings for 2011-2013

The State of the Air 2015 shows that progress in improving the nation’s air quality was mixed. Many cities experienced strong improvement and many others suffered worse episodes of unhealthy air. While most of the nation has much cleaner air quality than even a decade ago, a few cities even reported their worst episodes since the report began. Nearly 138.5 million people—almost 44 percent of the nation—live where pollution levels are too often dangerous to breathe. Fortunately, that represents fewer people exposed than in our previous 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, and to undermine the ability of the nation to fight for healthy air.

The State of the Air 2015 report looks at levels of ozone and particle pollution found in official monitoring sites across the United States in 2011, 2012, and 2013. 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 2014 report covered data from 2010, 2011, and 2012. More details about this process is in Methodology.1

Overall Trends

Thanks to stronger standards for pollutants and for the sources of pollution, the United States has seen continued reduction in 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. As the economy continues to grow after the recession, overall air emissions that create the six most widespread pollutants continue to drop.

Air emissions have dropped steadily since 1970 thanks to the Clean Air Act. As the economy continues to grow after the recession, emissions that contribute to the most widespread pollutants continue to drop. Source: U.S. EPA, Air Quality Trends, 2015
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Overall, the best progress came in the continued reduction of year-round particle pollution in the eastern half of the nation, thanks to cleaner diesel fleets and cleaner fuels used in power plants. Continued progress cleaning up pollution makes a difference, but a changing climate is making it harder to protect human health. Many cities had a record number of days with high short-term particle pollution, particularly in the West, where continuing drought and heat may have increased the dust, grass fires and wildfires, while burning wood as a heat source appears to contribute to the problem in many smaller cities. The impact of climate change is particularly apparent in the West where the heat and drought create situations ripe for episodes of high particle days. Fresno-Madera (CA) remained the most polluted metropolitan area for both year-round and short-term particle pollution, as it was in the 2014 report.

Many cities continued a decade of progress reducing ozone, but many others had more unhealthy air days. Communities will need more help to reduce ozone pollution in the warmer temperatures expected from the changing climate. Los Angeles remains as the metropolitan area with the worst ozone pollution, as it has for all but one of the 16 reports.

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 — Nearly 24 million people in the United States live in counties with unhealthful year-round levels of 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. More than 41 million people in the United States live where they suffered too many days with unhealthful levels of particle pollution.
  • Cleanest Cities — Only six cities made the cleanest list in all three categories, but several were among the cleanest in two.
  • People at Risk — More than four out of ten 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?

  1. A complete discussion of the sources of data and the methodology is included in Methodology.
Did You Know?

Did You Know?Particles are smaller than 1/30th the diameter of a human hair. When you inhale them, they are small enough to get past the body’s natural defenses.

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