The U.S. Environmental Protection Agency is proposing to tighten the air-quality standards for a type of air pollution sometimes called soot, and federal regulators are in Philadelphia Tuesday to hear opinions and comments from the public.

Oil and gas companies and clean air advocates are debating the "national ambient air quality standards for particulate matter" -- an official term for soot or pollution particles in the air.

Howard Feldman, the director of regulatory and scientific affairs for the trade group American Petroleum Institute, says the question before the EPA is: "What levels are considered to be acceptable, and what levels are considered to be unacceptable?"

Kevin Stewart with the American Lung Association of the Mid-Atlantic said the U.S. Clean Air Act requires the EPA to consider a completely different question: "Is the air quality healthful or not?"

Micrograms per cubic meter is a measure of the concentration of fine particles in the air. The EPA proposal would lower the standard to 12 or 13, down from 15.

Many areas across the Philadelphia region are below 15 now, but Stewart says health research show that standard is too weak to safeguard health.

"We might be telling people, according to the current standards, that we are meeting the air quality standards, which are supposed to be health-based standards. But when you look at all the science that's been amassed over the last decade or two, we are not meeting public health needs," Stewart said.

Industry groups are skeptical

Feldman is not convinced by the science.

"There's health evidence that cuts both ways. Right now, we don't think it is so compelling that EPA is required to tighten the standard right now," he said.

State and city officials are watching the EPA's deliberations closely; when a new standard is set, local governments have to come up with strategies to comply.

Feldman said it's important to remember that air-quality has improved steadily in recent decades.

"While air quality is improving, it's important to keep improving," said Kim Teplitzky, a spokeswoman with the Sierra Club. "Pollution gets in people's lungs and gathers there and can cause a whole host of problems that impacts people in their day-to-day lives."

Feldman said Pennsylvania refineries and other oil and gas companies worry that tougher air-quality standards would mean more counties would fail the standard.

"Non-attainment is not a good designation for jobs, job growth and the economy," Feldman said. "Some people say, 'Non-attainment means non-investment.'"

Questioning statistics, consequences

Air pollution expert Julie Goodman, a consultant for the American Petroleum Institute, is also set to testify at the EPA hearing.

A toxicologist with the Cambridge, Mass., environmental consulting firm Gradient, Goodman says the EPA's proposal to lower the standard relies too heavily on statistical studies "that look for relationships between measured air quality and a number of possible health metrics, such as hospital admissions," and did not fully consider other kinds of evidence.

The American Lung Association is hoping for tougher standards for both annual and daily levels of fine particles. Stewart said the change would save lives across Delaware, New Jersey, Pennsylvania, and West Virginia, according to the association's estimates. "They would prevent on the order of 5,000 premature deaths, 350 heart attacks, 3,500 hospitalizations and emergency department visits, 4,500 cases of acute bronchitis, 200,000 cases of aggravated asthma, and 400,000 days of missed work or school," he said in his written testimony.