A coalition of public health and environmental groups filed suit last week against the U.S. Environmental Protection Agency for failing to toughen the national standard for particulate matter pollution to a level that could prevent thousands of premature deaths every year.

Earthjustice, a nonprofit public-interest law firm, filed the suit on behalf of the American Lung Association, Environmental Defense and the National Parks Conservation Association. It's a response to the EPA's October decision to reject the advice of its own scientific advisory panel and staff scientists, who called for strengthening the existing standard of 15 micrograms per cubic meter for fine particulate matter to a more protective standard between 13 and 14 micrograms per cubic meter.

The current standard was set in 1997. The Clean Air Act requires the EPA to review air quality standards every five years and revise them based on the latest scientific information.

Scientists estimate that particulate pollution is responsible for tens of thousands of premature deaths nationwide every year by aggravating respiratory illnesses such as asthma, bronchitis, emphysema, and pneumonia. The pollution is also linked to premature deaths from other causes, such as lung cancer and heart disease.

Over 20 million people across the South live in areas where the air fails to meet federal health standards, according to the Southern Environmental Law Center. Particulate pollution also takes a heavy toll on the region's economy, SELC notes:

The Great Smoky Mountains National Park and the Shenandoah National Park continue to be ranked as the two most polluted parks in the country due to air pollution, leading to decreased visibility from the Park's ridges. The result is a heavy financial burden -- as much as $320 million annually in lost sales and tax benefits, and over 4,000 jobs -- for the mountain communities depending on tourism revenue from these parks.

"Anyone who questions the need to lower particulate matter pollution standards should take a hike in Great Smoky Mountains or Sequoia national parks in August," says Mark Wenzler, director of NPCA's Clean Air Program. "You will likely encounter a haze so thick you can barely see the next ridge. Imagine what that pollution is doing to your lungs."