"Emission factors used to paint a broad picture of air quality often underestimate pollution, evidence shows"
"Engineer Jim Southerland was hired by the U.S. Environmental Protection Agency in 1971 to join the nascent war on air pollution. He came to relish the task, investigating orange clouds from an ammunition plant in Tennessee and taking air samples from strip mines in Wyoming. Among his proudest accomplishments: helping the agency develop a set of numbers called emission factors — values that enable regulators to estimate atmospheric discharges from power plants, oil refineries, chemical plants and other industrial operations.
By the time Southerland left the EPA in 1996, he was “frustrated and ticked off,” he says, because the numbers he had helped develop were being misused. The original aim had been to paint a broad-brush picture of pollution. Instead, the numbers — meant to represent average emissions from industrial activities — were incorporated into permits stipulating how much pollution individual facilities could release. This happened despite EPA warnings that about half of these sites would discharge more than the models predicted. “These factors were not intended for permits,” says Southerland, now retired and living in Cary, North Carolina.
The number of emission factors used by the EPA since Southerland’s time has proliferated and stands at 22,693. The agency itself admits most are unreliable: It rates about 62 percent as “below average” or “poor.” Nearly 22 percent aren’t rated at all. About 17 percent earned grades of “average” or better, and only one in six has ever been updated. There is a slew of common problems, such as poor accounting for emissions from aging equipment."