Short-term Particle Pollution
What Are "Short-term Levels" of 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. Learn more about short-term particle pollution.
Twenty cities among the 25 most-polluted cities experienced fewer days when particle pollution levels spiked, a positive turnaround from the 2017 report when eight had reached their highest number of episodes ever.
One city that did better in 2014-2016 is Bakersfield, CA, which retains its ranking as the most polluted city for particle pollution spikes. Bakersfield has held this position for all but two years since the 2010 report, covering data from 2006-2008.
Four of the 20 cities improved to their fewest days ever on average of high particles in 2014-2016: Fresno- Madera, CA; Salt Lake City; Logan, UT; and Eugene, OR. Also improving over the 2017 report were: San Jose-San Francisco; Los Angeles; Phoenix; Denver; Visalia-Porterfield, CA; Fairbanks, AK; Modesto-Merced, CA; Missoula, MT; Lancaster, PA; Anchorage, AK; South Bend, IN; Yakima, WA; Sacramento, CA; Reno-Carson City, NV; and Harrisburg-York-Lebanon, PA.
Four cities suffered more spikes in particles in 2014-2016: El Centro, CA; Pittsburgh; Seattle; and Salinas, CA. One city—Indianapolis—remained the same.
Regional differences. Western states, especially California, but also Utah, Montana, Arizona, Colorado and Washington have multiple or large cities on this list. Some reflect ongoing experiences with emissions from high emitting sources trapped by weather inversions that do not allow them to blow away, including, for example, Bakersfield, Visalia, Fresno and Modesto-Merced. Others, like some in California and Missoula, MT, reflect increased wildfires built from the ongoing low rainfall and climate impacts. Several include areas with high use of wood-burning or solid-fuel-burning stoves, including two cities in Alaska—Fairbanks and Anchorage—as well as Logan, UT, and Eugene, OR.
In the eastern states, most of the cities listed here are cities with high year-round levels as well, with three cities in Pennsylvania and two in Indiana on this list. Weather patterns here, too, may have helped build up particles to unhealthy short-term levels.
Data remain missing for Illinois and Mississippi here as well. Most of the other states have at least some data.