U.S. Environmental Protection Agency (EPA) has just proposed updates to its national air quality standards for harmful fine particle pollution, including soot (known as PM2.5). These microscopic particles can penetrate deep into the lungs and have been potentially linked to a wide range of serious health effects, including premature death, heart attacks, and strokes, as well as acute bronchitis and aggravated asthma among children. A federal court ruling required EPA to update the standard based on best available science. The current proposal, which meets that requirement, builds on steps already taken by the EPA to slash dangerous pollution in communities across the country. Thanks to these steps, 99 percent of U.S. counties are projected to meet the proposed standard without any additional action.