Physicians for Social Responsibility-Los Angeles and Sierra Club, represented by Earthjustice, have filed a lawsuit in U.S. District Court for the Central District of California in Los Angeles against the U.S. Environmental Protection Agency (EPA) for its failure to act on the South Coast Air Quality Management District’s plan to reduce particulate matter, or soot.

A decision on whether to approve the plan, in part or in full, should have been completed by August 13, 2014. The agency’s inaction has left a heavily polluted region without guidance on how to meet federal protections for soot. The California Air Resources Board submitted the South Coast’s 2012 Air Quality Management Plan for review under the EPA’s 2006 standard on February 13, 2013.

Soot is one of the most dangerous forms of air pollution, consisting of tiny particles from dirty sources like diesel exhaust, agricultural activities, heavy industry, and power plants. These tiny particles are easily inhaled deep into the lungs and absorbed into the bloodstream where they cause a host of illnesses. According to the Environmental Protection Agency, breathing in fine particulate matter has been linked to premature death, heart attacks, irregular heartbeat, aggravated asthma, decreased lung function and increased respiratory symptoms. What’s worse is that children and elderly are at increased risk.