Unconventional extraction of natural gas has been increasingly examined as a source of methane, a potent greenhouse gas.  However, unconventional shale gas extraction is also an energy- and water-intensive process that can generate significant emissions of reactive nitrogen (N), mainly nitrogen oxides (NO = NO + NO₂) and ammonia (NH₃).  In this study, we examine through modeling and rare empirical observations from a research wellpad, the influence of shale gas extraction on regional and local air quality, respectively and the potential impact of these emissions to critical loads of atmospheric N deposition. 

The Marcellus Shale is Devonian rock formation found in Maryland, New York, Ohio, Pennsylvania, and West Virginia that is producing roughly 430,000 m³ of natural gas per day (U.S. EIA, 2016).  NO_x and NH₃ emissions can originate from wellpad development, vehicular traffic to the wellpad site, and large diesel generators used to power drilling rigs, pumps, and compressor stations.  Existing studies on reactive N emissions from Marcellus employ either:  1) literature-based emission factors to model NO_x emissions or 2) measure relative changes in ambient air concentrations in areas of shale gas extraction.  Here in this study, we use natural stable isotope tracers associated with fossil fuel combustion to examine the fluxes and relative extent of NO₂ and NH₃ emissions across a wellpad and road transect.  Using a spatially explicit model, we assess the potential impact of Marcellus shale NO_x emissions to regions of Pennsylvania recovering from historically high rates of atmospheric deposition.