The facts overwhelmingly document that the total amount of air pollutants going into Pennsylvania's air fell substantially between 2008 and 2011. And this good news happened, mainly because of gas displacing coal to make electricity and because of more coal plants being retrofitted with modern pollution controls. More renewable energy and energy efficiency also helped.
While gas is contributing to a net decrease in 5 key air pollutants (sulfur dioxide, soot, carbon monoxide, nitrogen oxides, and volatile organic compounds), gas production itself does emit air pollutants. See table in:
http://thebreakthrough.org/index.php/programs/energy-and-climate/deadly-air-pollution-declines-thanks-to-gas-boom/. Using Pennsylvania Department of Environmental Protection data in the table in the linked to story, I calculated the portion of the statewide total air emissions from point sources for the 5 pollutants in the table for which gas production itself is responsible.
For sulfur dioxide, as of 2011, gas production was responsible for essentially 0% of the statewide total from point sources, since producing gas emitted 122 tons of sulfur dioxide out of a statewide total of 353,480 tons.
For soot, natural gas production emitted in 2011 3% of the statewide total from point sources. It is important to note that soot also is pumped into the air from transportation sources and so gas production emitted less than 3% of the total soot discharged into our air.
For carbon monoxide, natural gas production accounted for 8% of the statewide total from point sources.
For nitrogen oxides, natural gas production was responsible for 9% of the statewide total from point sources.
And for volatile organic compounds, natural gas production emitted 14% of the statewide total from point sources.
Two further points should be made. Gas production is concentrated in particular counties. As a result, in some counties gas production likely emits more volatile organic compounds or nitrogen oxides than any other point source.
Most importantly, air pollutants from gas production can be slashed by up to 90% by requiring the installation of the best available pollution controls at compressor stations, green completions, not using diesel to operate engines, and excellent maintenance programs. Regulators and the gas industry itself should implement these available pollution control measures and cut further the environmental footprint of gas.