The U.S. Environmental Protection Agency is holding public hearings in two cities to gather testimony on its proposed standard for soot, or fine particle air pollution.

The first is today in Philadelphia. A fitting place. According to the American Lung Association, this region ranks tenth in the nation when it comes to soot pollution.

Dozens of people signed up to speak, from the American Lung Association to the American Petroleum Institute, from the Moms Clean Air Force to the American Forest and Paper Association, Earthjustice to the National Cattlemen's Beef Association.

As often happens at these hearings, a consortium of environmental and health advocates gathered for a mid-day rally and stroller brigade, and not even the blistering heat -- and an air action day -- kept them away.

"On hot, humid days like today we are especially at risk from air pollution like soot which poses a serious threat to our children and people with asthma like my young nephew who I've seen first-hand deal with the challenges of not being able to breathe well. We're here today to show our support for stronger limits on soot pollution that will clean up our air and mean healthier families in Philadelphia," said Jackie Wilson, a volunteer with the Philadelphia Sierra Club, as quoted in a press release about the event.

Coal-fired power plants, diesel exhaust and petroleum refineries are significant sources of soot. The chemical-laden particles travel deep into the lungs and can exacerbate many health problems, causing heart attacks and strokes and initiating asthma attacks. Thousands of premature deaths a year are blamed on soot.

"Soot is so small that its very nature makes it one of the most dangerous forms of air pollution. It is easily inhaled where it can then enter the bloodstream and contribute to heart attacks, strokes and asthma attacks. Young children, like mine, are especially susceptible to soot as they breathe more rapidly and inhale more dangerous particulate matter," said Gretchen Alfonso, a mother of two from Pennsport who represents the Mom's Clean Air Force in Philadelphia.

However,  Howard Feldman, director of regulatory and scientific affairs for the American Petroleum Institute, testified that the EPA had not proved a cause and effect between soot and health effects. He also said that the current, less-restrictive standard, would continue to produce benefits. "Taken as a whole, the scientific studies cut in different directions…. There is no need to move the goalposts now," he said, according to an API press release.

Kevin M. Stewart, director of environmental health for the American Lung Association of the Mid-Atlantic, testified that "Opponents of improving air quality standards complain of purported undue costs to the economy. Yet not only does history show no evidence that setting strong pollution standards hurts jobs for the economy as a whole, but rather that failure to clean up air pollution imposes all sorts of costs on the economy in death, disease, disability, absenteeism, and lost work and productivity. Far from being a ―job-killer,‖ improving air quality is actually a great bargain, with benefits exceeding clean-up costs typically by a factor on the order of thirty to one."