Impacts of Marcellus Shale Natural Gas Production on Regional Air Quality

Natural gas is a clean burning alternative to other fossil fuels, producing lower carbon dioxide (CO₂) emissions during combustion. Gas deposits located within shale rock or tight sand formations are difficult to access using conventional drilling techniques. However, horizontal drilling coupled with hydraulic fracturing is now widely used to enhance natural gas extraction. Potential environmental impacts of these practices are currently being assessed because of the rapid expansion of natural gas production in the U.S. Natural gas production has contributed to the deterioration of air quality in several regions, such as in Wyoming and Utah, that were near or downwind of natural gas basins. We conducted a field campaign in southwestern Pennsylvania on 16-18 June 2012 to investigate the impact of gas production operations in the Marcellus Shale on regional air quality. A total of 235 whole air samples were collected in 2-liter electropolished stainless- steel canisters throughout southwestern Pennsylvania in a regular grid pattern that covered an area of approximately 8500 square km. Day and night samples were collected at each grid point and additional samples were collected near active wells, flaring wells, fluid retention reservoirs, transmission pipelines, and a processing plant to assess the influence of different stages of the gas production operation on emissions. The samples were analyzed at Appalachian State University for methane (CH₄), CO₂, C₂-C₁₀ nonmethane hydrocarbons (NMHCs), C₁-C₂ halocarbons, C₁-C₅ alkyl nitrates and selected reduced sulfur compounds. In-situ measurements of ozone (O₃), CH₄, CO₂, nitric oxide (NO), total reactive nitrogen (NO_y), formaldehyde (HCHO), and a range of volatile organic compounds (VOCs) were carried out at an upwind site and a site near active gas wells using a mobile lab. Emissions associated with gas production were observed throughout the study region. Elevated mixing ratios of CH₄ and CO₂ were observed in the southwest and northeast portions of the study area indicating multiple emission sources. We also present comparisons of VOC fingerprints observed in the Marcellus Shale to our previous observations of natural gas emissions from the Denver-Julesburg Basin in northeast Colorado to identify tracers for these different natural gas sources.