There was an average of 20 days per year between 2013 and 2015 when the air was considered unhealthy because of particle pollution, the recent data showed.
Janice Nolen, the lead author of the ALA report, told Business Insider that local problems like auto traffic can make cities' ozone or particle problems worse, but that the overall issue is a national one.
For particle pollution, the association has data only for Lackawanna and Monroe counties in Northeast Pennsylvania. California's Visalia-Porterville-Hanford was an area where levels worsened and has the dubious title as the most-polluted city for year-round particle pollution. Summit and Stark counties each had one day, which ranked the region 49 among 186 metropolitan areas in the country, according to the report. In Hillsborough County, the number of unhealthy ozone days dropped from eight to four. Particulate pollution, which includes matter such as dirt, dust, and soot, can often have similar root causes, including manufacturing, construction, and automobile use. It is harmful to children, seniors and those with asthma and other lung diseases.
Kent County and Sussex County received A's for their measure of daily fine particle pollution.
It has no unhealthy ozone days and one of the lowest year-round particle pollution levels.
The 2017 State of the Air report put San Luis Obispo County on the map, but not for a good reason.
"The Clean Air Act must remain intact and in force", Nolen said.
The most notable national findings of the 18th annual report were lower overall ozone levels and year-round particle levels, the report said.
Dawn Mullally, director of air quality at the ALA's Colorado chapter, said while some 125 million Americans continue to experience unsafe levels of air pollution, it's clear that rules limiting toxic emissions are paying off.
Approximately 125 million Americans live in areas where they are exposed to dangerously high levels of air pollution, a considerable decline from the year before.
"The air is cleaner, but not clean enough to protect people from increased risks of premature death, asthma attacks and lung cancer that research shows comes from breathing these pollutants", Bryan said in a statement. President Donald Trump has proposed cuts to federal climate science funding and has deregulated industries that are a major source of risky emissions.
"Even though this is the third year in a row where New Castle County did improve its ozone levels to the best ever, it still averaged about six days a year when the ozone levels were in the unhealthful range for people in those sensitive groups", said Stewart.
He said the Clean Air Act is responsible for the improvements we're seeing in air quality in DE and nationwide.
In California and nationwide, the number of unhealthy days for ozone has decreased, thanks, says the Lung Association, to the success of the federal Clean Air Act as well as state and local air pollution control programs that clean up major sources of emissions.