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.
Fifteen 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 2013-2015. The 10 most polluted remain the only metropolitan areas in the nation that fail to meet the official national limits on annual fine particle pollution.
Eight of the 25 cities suffered higher annual particle pollution levels, including Visalia-Porterville-Hanford, CA, the city that ranked as the most polluted for year-round levels. In addition to Visalia, 3 other California cities –Bakersfield; San Jose-San Francisco; and San Luis Obispo – and 2 other cities in the western states-- Medford-Grants Pass, OR, and Fairbanks, AK had worse year-round levels. The two remaining cities with higher year-round average levels were in the east: Johnstown-Somerset, PA and New York City metro area. San Luis Obispo reached its worst level ever.
Two cities in the list of the 25 most polluted maintained the same level as in the 2016 report: Cleveland and Houston.
Twelve cities improved to their lowest levels of year-round particle pollution.
Regional differences. Much of the eastern and middle parts of the country have improved significantly since the report first started to track these fine particles. Much of that improvement came from reducing emissions from coal-fired power plants, as well as benefiting from nationwide cleanup of diesel engines. However, the western states’ burden of so much wildfire smoke and high inversions seems to have moved from just being a short-term problem to adding to the burden year-round. Cities in California’s San Joaquin valley were hit hard, as were other locations where particle pollution is usually limited to the short spikes, including Fairbanks, AK, and Medford-Grants Pass, OR.
Data remain missing in all of Illinois, most of Tennessee and parts of Maine. That means that millions of people, including in large cities Chicago, Memphis and St. Louis (which is missing suburban counties in Illinois), cannot know how much particulate matter they are breathing.