New data shows that air quality across the United States is dropping after many years of improvement. Over the last two years, the U.S. had more polluted air days than just a few years earlier, official data showed. The information was collected by the Environmental Protection Agency, or EPA, and examined by the Associated Press. Climate experts say it is too early to know whether the recorded drops are the beginning of a long-term situation. But health officials say it is troubling to see the changes following years of progress. In 2017 and 2018, there were 15 percent more unhealthy air days than in the previous four years, the data shows. The 2013-2016 period saw the fewest number of unhealthy air days the U.S. had ever had since at least 1980. Air quality is affected by a complex mix of conditions, both natural and man-made.
