Over the past decade, significant development in shale gas extraction technologies has led to a massive increase in oil and gas production within the Barnett Shale region in North Texas. This region abuts a fast-growing Dallas-Fort Worth urban area with increasing air quality concerns. Air quality information for 2011-2015 from two urban and three non-urban monitoring sites within the Barnett Shale region were analyzed to identify the spatial and temporal trends of volatile organic compounds (VOC) concentrations. The non-urban sites had higher mean concentrations of total non-methane organic compounds (TNMOC) at 123.6 ppb-C than 77.06 ppb-C at the urban sites. Alkanes, which includes ethane, propane and n-butane, were the dominant VOC group at all five monitoring sites, with 88% of TNMOC at urban sites and 95% at the non-urban sites. Alkenes, alkynes and aromatics composition at urban sites accounted for 3.96%, 0.72% and 4.72% of TNMOC, and at the non-urban sites these were 1.55%, 0.43% and 1.94%, respectively. Seasonal variations were noted in the VOC profiles with high concentrations during the winter months and low during summer months. The alkane/TNMOC ratio also showed a similar seasonal pattern, with a median value of 0.8 at the urban sites and 0.9 at non-urban sites. Alkene/TNMOC ratios were highest during the summer months, while alkyne/TNMOC ratios were highest during spring and low in winter, due to the influence of localized urban emissions. Higher concentrations of isoprene were measured at one of the urban sites as a result of biogenic emissions from nearby urban forests. Spatial and temporal analysis of measured VOC concentrations at ambient air monitoring stations in North Texas revealed strong influence of source regions with high oil and gas activities in close proximity.
Keywords: Air quality; Barnett Shale; North Texas; Shale gas; VOC.
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