Year-round Particle Pollution
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. Learn more about year-round particle pollution.
Eighteen of the 25 cities with the highest year-round particle pollution reduced their levels, including 12 that reached or matched their lowest levels ever in 2014-2016. The 11 most polluted remain the only metropolitan areas in the nation that fail to meet the official U.S. national limits on annual fine particle pollution. However, all 25 failed to meet the more protective standards established by the World Health Organization.
Twelve of 25 most-polluted cities reached or tied their lowest average levels of particle pollution: Fresno-Madera, CA; Modesto-Merced, CA; Cleveland; Philadelphia; Indianapolis; Detroit; Houston; Cincinnati; Johnstown-Somerset, PA; Louisville; Knoxville, TN; and Little Rock, AR.
Six others improved over the 2017 report: Visalia-Porterfield-Hanford, CA; Bakersfield, CA; El Centro, CA; San Jose-San Francisco; San Luis Obispo, CA; and Atlanta.
Fairbanks, AK, moved to the most-polluted city for the first time. Previously ranked as #17 most polluted, Fairbanks' improved monitoring in the borough now identifies that this problem is more severe than previously known. Six other cities in the 25 most polluted had higher particle levels year-round: Los Angeles; Pittsburgh; Lancaster, PA; Birmingham, AL; Harrisburg-York-Lebanon, PA; and Las Vegas.
Eleven of 25 most-polluted cities reached or tied their lowest average levels of particle pollution.
Regional differences. Long-ranked on the short-term particle list, Fairbanks' new placement atop the year-round list shows the impact of sustained use of its chief source of particle pollution—burning of wood and other solid fuels to heat homes. They are making steps to change out old, dirty stoves for cleaner ones. Fairbanks is in a unique situation where wood- and solid-fuel-burning comprise the biggest sources and where the presence of snow can create weather inversions that trap particles in place.
Eight of the top 11 most-polluted cities are in California, including several in the Central Valley, where particles produced by agricultural production and transportation can easily be trapped by the physical terrain. Progress there is due to the aggressive work of the state and local officials.
A large concentration of cities with high levels also exists in the states lining the Great Lakes, especially Pennsylvania, Ohio, Indiana, and Michigan. (If it had data, possibly Illinois would be in that list). While all these cities have levels that meet the national air quality standard in the U.S., all have levels above the limit recommended by the World Health Organization. Much of their high particle levels likely come from coal-fired power plants, which line the region, as well as diesel emissions from transportation sources including heavy-duty trucks, rail and marine fleets using the Lakes for transport. Others in Kentucky, Tennessee, Georgia and Arkansas also had particles from power plants as a significant source.
Data remain missing on particle pollution in all of Illinois as it has since our 2014 report covering 2010-2012 data. That means that large cities, including Chicago and St. Louis (which is missing suburban counties in Illinois), have not known how much particulate matter they are breathing for four years. Data are now missing from all of Mississippi and two large counties in California: Los Angeles County and San Bernardino County. The new information on the extremely high levels in Fairbanks shows how important these data are to protecting health.
- Hamra GB, Guha N, Cohen A, Laden F, Raaschou-Nielsen O, Samet JM, Vineis P, Forastiere F, Saldiva P, Yorifuji T, Loomis D. Outdoor particulate matter exposure and lung cancer: A systematic review and meta-analysis. Environ Health Perspect. 2014; 122: 906-911.