The "State of the Air" 2019 found that, in 2015-2017, more cities had high days of ozone and short-term particle pollution compared to 2014-2016 and many cities measured increased levels of year-round particle pollution.
The "State of the Air" 2019 report adds to the evidence that a changing climate is making it harder to protect human health. The three years covered in this report ranked as the hottest years on record globally. High ozone days and spikes in particle pollution zoomed, putting millions more people at risk and adding challenges to the work cities are doing across the nation to clean up.
The 2019 report—the 20th annual release—uses the most recent quality-assured air pollution data, collected by the federal, state and local governments and tribes in 2015, 2016 and 2017. The "State of the Air" 2019 report looks at levels of ozone and particle pollution found in official monitoring sites across the United States in 2015, 2016 and 2017. For comparison, the "State of the Air" 2018report covered data from 2014, 2015 and 2016.1 The report uses the most current quality-assured nationwide data available for these analyses.
The report examines particle pollution (PM2.5) in two separate ways: averaged year-round (annual average) and short-term levels (24-hour). For both ozone and short-term particle pollution, the analysis uses a weighted average number of days that allows recognition of places with higher levels of pollution. For the year-round particle pollution rankings, the report uses averages calculated and reported by the U.S. Environmental Protection Agency (EPA).
The "State of the Air" 2019 found that ozone and short-term particle pollution worsened in many cities in 2015-2017, compared to 2014-2016. Even levels of year-round particle pollution increased in some cities.
Cleanest U.S. Cities
Six cities ranked on all three cleanest cities lists for ozone, year-round particle pollution and short-term particle pollution. They had zero high ozone or high particle pollution days and were among the 25 cities with the lowest year-round particle levels. Four have repeated their ranking on this list, but two join this list for the first time in years. Listed alphabetically below, these six cities are:
Eight other cities ranked among the cleanest cities for both year-round and short-term levels of particle pollution. That means they had no days in the unhealthy level for short-term particle pollution and were on the list of the cleanest cities for year-round particle pollution. Listed alphabetically below, they are:
Nineteen other cities ranked among the cleanest for ozone and short-term particle pollution. That means they had no days in the unhealthy level for ozone or for short-term particle pollution. Listed alphabetically below, they are:
Four cities ranked on both lists for ozone and year-round particle pollution levels. These cities had no days in the unhealthy level for ozone pollution and were on the list of the cleanest cities for year-round particle pollution. Listed alphabetically below, they are: