As local, federal, and international policies targeting the quality of the air we breathe continue to evolve, questions arise of how effective existing policies have been in improving human health. For example, how many lives have been saved by tough air pollution policies? How many illnesses have been caused by lax policies?

Annual mean levels of fine particulate matter (PM2.5) pollution declined in the United States between 1990 (left) and 2010 (right), leading to thousands of lives saved, according to researcher Jason West.