Year Round Particle Pollution

More than 46.2 million people (14.7%) in the United States live in an area with unhealthful year-round levels of particle pollution.

These people live in areas where chronic levels are regularly a threat to their health. Even when levels are fairly low, exposure to particles over time can increase risk of hospitalization for asthma, damage to the lungs and, significantly, increase the risk of premature death.

What Is Year-Round Particle Pollution?

Particle pollution is a mix of very tiny solid and liquid particles in the air. "Year-round" refers to an annual average level that represents the concentration of particles day-in and day-out. To learn more, go to Health Risks.

In 2010-2012, many places made strong progress over 2009-2011. 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.

  • Among the 25 cities with the worst year-round levels of particle pollution, 18 had lower levels in 2010-2012, while five recorded higher annual levels and two cities maintained the same level.1 However, all of the most polluted cities continue to have year-round particle levels that violate health-based standards.
  • Fresno-Madera (CA) recorded higher annual particle levels and became the most polluted in the nation for year-round particle pollution. Four other saw their year-round levels increase from previous reports:2 El Paso-Las Cruces (TX-NM), Phoenix, Birmingham, and San Diego.
  • Thirteen cities improved to their lowest annual levels in this report: Visalia-Porterville-Hanford (CA), Los Angeles, Pittsburgh, Philadelphia, Cincinnati, Louisville, Cleveland, Wheeling (WV), Indianapolis, Columbus (OH), Dayton (OH), Johnstown (PA) and Bakersfield (CA), which had been the most polluted city for year round particle levels for 4 of the last 5 reports.
  • Three of the other most-polluted cities matched or maintained the lowest levels they had previously achieved, reflecting stalled progress toward healthier air. Atlanta improved to return to its lowest level as in previous reports, St. Louis maintained the same levels it had reached in the 2013 report, and Chicago maintained the same levels it had reached in both the 2012 and 2013 reports.
  • Four cities improved over the previous levels, but had reported cleaner air in the past: Modesto-Merced (CA), El Centro (CA), New York City and Macon (GA).

» 25 Most Ozone-Polluted Cities
» 25 Cleanest Cities for Ozone


1 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.

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

FACT: Nearly 27.8 million people live in counties that got an F for all three measures: ozone, year-round particle pollution and short-term particle pollution.

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