Pennsylvania's shale gas industry was responsible for about 4 percent of the total air pollution emitted by all industrial facilities in 2011, according to a first-ever inventory taken by state environmental regulators.
Drillers and other companies involved in the extraction, processing and transportation of natural gas from the Marcellus Shale accounted for nearly 9 percent of the nitrogen oxides and nearly 14 percent of the volatile organic compounds emitted from all so-called "point" sources of pollution statewide, according to the Department of Environmental Protection tally.
Under federal law, DEP is required to report statewide air emissions to the U.S. Environmental Protection Agency every three years; 2011 was the first year in which DEP required the shale gas industry to report emissions.
The survey does not take emissions from cars and trucks — the single largest source of air pollution — into account. Nevertheless, it provides an initial snapshot of air pollution caused by drilling rigs, fracking operations, compressor stations and other elements of natural gas production in Pennsylvania's vast Marcellus Shale formation.
The industry produced 16,542 tons of nitrogen oxides and 2,720 tons of volatile organic compounds in 2011, according to the report. By comparison, power plants were a far bigger source of air pollution, contributing 142,749 tons of nitrogen oxides and far greater amounts of soot, carbon monoxide and other pollutants.
Nitrogen oxides are produced during combustion — primary culprits are vehicle exhaust and electrical power plants — and can worsen respiratory conditions like bronchitis and asthma. They also combine with VOCs to form unhealthy ground-level ozone, or smog.
The drilling industry pointed to the numbers as evidence it is having a small impact on air pollution. But some environmentalists expressed concern Friday.
Kevin Stewart, a member of the DEP advisory committee, said he's concerned that shale gas will result in an increasing amount of air pollution as more wells are drilled and fracked and more processing plants, pipelines and compressor stations are built.