Year Round Particle Pollution

More than 44.3 million people (14%) 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.

In 2009-2011, many places made strong progress over 2008-2010, 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, especially in the eastern U.S.  Still, the science shows that annual particle levels need to be much lower, as shown in the EPA’s decision in December 2012 to strengthen the national air quality standards for fine particles for the first time in fifteen years.  

  • 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.
    Eighteen cities had lower year-round levels of particle pollution in 2009-2011, including 16 with their lowest levels recorded.2  
  • Bakersfield (CA) recorded its lowest levels ever in 2009-2011, but tied with Merced (CA) as cities with the worst year-round levels of particle pollution in the nation. Also on this list are fifteen other cities that reported their lowest levels of year-round particle pollution: Hanford (CA); Los Angeles; Visalia (CA); Pittsburgh; Cincinnati; Philadelphia; St. Louis; Louisville; Canton (OH); Cleveland; Indianapolis; Steubenville (OH); Wheeling (WV); Birmingham; and Dayton (OH). Fairbanks (AK) and Phoenix improved over the previous levels, but had reported cleaner air in the past.
  • Unfortunately, seven cities saw their year-round levels increase from previous reports.1 Top of that list is Merced, where year-round levels of particle pollution increased to their worst reading ever to tie Bakersfield for most polluted city. Other cities with worse annual levels were Fresno, Modesto (CA), El Centro (CA), Macon (GA), Allentown (PA), and Atlanta.

Thanks in part to legal action taken by the American Lung Association, EPA strengthened the long- outdated limits on year-round particle pollution in December, 2012. That crucial step will drive more protection from deadly particles.

» 25 Cities Most Polluted by Year-round Particle Pollution
» 25 Cleanest Cities for Year-round Particle Pollution


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.