The air quality in the United States is dramatically declining, leaving about 150 million people -- nearly half of America's population -- breathing unhealthy, heavily polluted air, according to the newly released "State of the Air" 2020 report by the American Lung Association. The “State of the Air” 2020 found that, in 2016-2018, more cities had high days of ozone and short-term particle pollution compared to 2015-2017 and many cities measured increased levels of year-round particle pollution. 2020 marks the 50th anniversary of the Clean Air Act, the landmark law that has driven dramatic improvements in air quality over its history. This is critical because far too many communities reported air pollution that still threatens health, and climate change impacts continue to threaten to progress. Further, harmful revisions and setbacks to key protections currently in place or required under the Act threaten to make air quality even worse in parts of the country. “State of the Air” 2020 shows that we must not take the Clean Air Act for granted. The “State of the Air” 2020 report shows that too many cities across the nation increased the number of days when particle pollution, often called “soot,” soared to often record-breaking levels. More cities suffered from higher numbers of days when ground-level ozone, also known as “smog,” reached unhealthy levels. Many cities saw their year-round levels of particle pollution increase as well.