Notably, the large wildfires of 2018 aren't included in this data, said Nolen, who has worked on State of the Air every year for the past 20 years. A new study released Wednesday shows things aren't getting better.
The new report looked at levels of ozone, annual and short-term particle pollution (the latter of which lingers for 24 hours). The report noted that wildfires impact air quality.
The annual "State of the Air" report tracks Americans' exposure to unhealthful levels of ozone or particle pollution, both of which can be deadly. The New York-Newark metro area remained the 10th worst in the nation for ozone, while the Philadelphia-Reading-Camden area was the 21st worst, three spots worse than last year's report.
"Denver residents should be aware that we're breathing unhealthy air, placing our health and lives at risk", said American Lung Association director of advocacy JoAnna Strother.
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California claimed seven of the top 10 most ozone-polluted cities, with Los Angeles topping the list for the 19th time. "The American Lung Association calls on the Administration and Congress to protect and prioritize Americans' health by taking urgent action to fight air pollution and address climate change".
Lehigh County got a D for ozone; its particle results were incomplete. Those with the lowest pollution levels were primarily along the northern California coast, and lesser populated areas near the OR border. Because ground-level ozone is formed by chemical reactions between precursor pollutants in the presence of heat and sunlight, a higher number of hot, sunny days means unhealthier levels of ozone. California dominated the list of most-polluted cities. Ozone attacks the lungs - some people describe ozone pollution as "sunburn for the lungs". Climate change poses many threats to human health, including worsened air quality and extreme weather events.
Only six cities qualified for Cleanest US Cities: Bangor, Maine; Burlington-South Burlington, Vermont; Honolulu, Hawaii; Lincoln-Beatrice, Nebraska; Palm Bay-Melbourne-Titusville, Florida; and Wilmington, North Carolina.