Professor John Balmes, close colleague and friend, and physician member of the California Air Resources Board:

PM 2.5 kills people. There has been little dispute that microscopic particulate matter in air pollution penetrates into the deepest parts of the lungs and contributes to the early deaths each year of thousands of people in the United States with heart and lung disease.

One recent study called PM 2.5 “the largest environmental risk factor worldwide,” responsible for many more deaths than alcohol use, physical inactivity or high sodium intake.

The Environmental Protection Agency’s own website says: “Numerous scientific studies have linked particle pollution exposure to a variety of problems, including: premature death in people with heart or lung disease, nonfatal heart attacks, irregular heartbeat, aggravated asthma, decreased lung function, increased respiratory symptoms.”

Which makes it deeply troubling that the very people at the helm of the Trump administration’s E.P.A. responsible for protecting public health and the environment are now pursuing a course that would make the air we breathe even more hazardous.