Short Term Particle Pollution

More than 44.1 million people in the United States live in an area with too many days with unhealthful levels of particle pollution.

What Is Short-Term Particle Pollution?

Particle pollution can be harmful even if it is inhaled over just a few hours or days, even if the year-round averages are low. "Short-term levels" refers to just such spikes. These represent levels averaged over a 24-hour period. Those days or weeks of high levels can be dangerous, even deadly. To learn more, go to Health Risks.

More than 14 percent of Americans live in 50 counties that experienced too many days with unhealthy spikes in particle pollution, a decrease from the last report. Short-term spikes in particle pollution can last from hours to several days and can increase the risk of heart attacks, strokes and emergency room visits for asthma and cardiovascular disease, and most importantly, can increase the risk of early death

Progress continued in most cities in the long-term trend for fewer days with high particle pollution, but not all.1 Two thirds of the most–polluted metros recorded fewer unhealthy days on average than in 2009-2011. Although year-round average levels for particles are steadily dropping, the trend for short-term spikes in high particle counts can vary from year. Spikes often occur in the winter, as has happened in Fairbanks (AK) and Salt Lake City in recent winters. In some cities, these spikes come from increased burning of wood and other fuels in the winter for heat, often in highly-polluting indoor wood stoves or outdoor wood boilers.

Sixteen cities most polluted by short-term particle pollution had fewer high particle days on average in 2010-2012 compared to 2009-2011 and seven had their fewest days on average ever in the history of the report.

  • Although one of the seven measuring their fewest ever unhealthy days on average, Fresno-Madera (CA) moved up to rank as the most polluted for short-term particle levels. Other cities reporting their fewest unhealthy days are: Pittsburgh, Salt Lake City, Harrisburg (PA), San Diego, Sacramento (CA) and Bakersfield (CA).2
  • Nine other metropolitan areas also had fewer days of unhealthy particle pollution in 2009-2011 than in the last report: Visalia-Porterfield-Hanford (CA), Los Angeles, Modesto-Merced (CA), Fairbanks (AK), Logan (UT), Davenport (IA), Seattle, Green Bay (WI) and South Bend (IN).
  • Nine metropolitan areas suffered additional high particle days compare to last year's report, including San Francisco, Chicago, Phoenix, Indianapolis, New York City and Lancaster (PA). Three cities had their worst average number of days ever – El Paso-Las Cruces (TX-NM), Missoula (MT), and Yakima (WA).

» 25 Cities Most Polluted by Short-Term Particle Pollution
» 25 Cleanest Cities for Short-Term Particle Pollution


1 These trends are based on prior available data. Not all cities had counties with complete annual averages posted for all prior years.

2 Note that the full metropolitan areas often include multiple counties, incorporated cities and counties in adjacent states, as the Office of Management and Budget defines them. Not all counties in any metro area will have monitors.

FACT: Steps you can take to improve air quality will also help fight climate change. Drive less. Don’t burn wood or trash. Use less electricity. Make sure your school system requires clean buses.

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