Abstract
Oil and natural gas operations have continued to expand and move closer to densely populated areas, contributing to growing public concerns regarding exposure to hazardous air pollutants. During the Barnett Shale Coordinated Campaign in October, 2013, ground-based whole air samples collected downwind of oil and gas sites revealed enhancements in several potentially toxic volatile organic compounds (VOCs) when compared to background values. Molar emissions ratios relative to methane were determined for hexane, benzene, toluene, ethylbenzene, and xylene (BTEX compounds). Using methane leak rates measured from the Picarro mobile flux plane (MFP) system and a Barnett Shale regional methane emissions inventory, the rates of emission of these toxic gases were calculated. Benzene emissions ranged between 51 ± 4 and 60 ± 4 kg h-1. Hexane, the most abundantly emitted pollutant, ranged from 642 ± 45 to 1070 ± 340 kg h-1. While observed hydrocarbon enhancements fall below federal workplace standards, results may indicate a link between emissions from oil and natural gas operations and concerns about exposure to hazardous air pollutants. The larger public health risks associated with the production and distribution of natural gas are of particular importance and warrant further investigation, particularly as the use of natural gas increases in the United States and internationally.
Highlights
In recent years the development of energy from unconventional oil and natural gas (ONG) sources has grown substantially and has been hailed by some as an effective CO2 mitigation strategy.[1]
Oil and natural gas (ONG) sample locations included natural gas well pads (n = 31), some of which housed separators, condensate tanks, or compressors in addition to the well heads; conventional oil wells (n = 12); compressor stations (n = 10); distribution city gates and storage facilities (n = 5); and gathering and processing facilities (n = 3)
For each of the ONG sources sampled in this study, volatile organic compounds (VOCs) were enhanced from 2 to nearly 50 times over background (Table 1)
Summary
In recent years the development of energy from unconventional oil and natural gas (ONG) sources has grown substantially and has been hailed by some as an effective CO2 mitigation strategy.[1]. In a second approach for estimating the regional C6H6 flux, CH4 emission rates are taken from the spatially resolved emissions inventory developed for the entire Barnett Shale.[29] Background corrected VOC mixing ratios were used to determine source-specific molar ratios relative to CH4, as was previously done to estimate regional ethane emissions.[31] Average molar ratios (Table S3) help to lessen biases that arise from sampling only those ONG sites with larger leak rates These “fat-tail” sites (including well pads, compressors, and processing facilities) contribute roughly 20% of ONG emissions hin−1t,heofrewghioicnh.2967O%vecroamll,ethferoBmartnheetrtmSohgaleeneicmsiotsur7c2e,s3,0o0rk4g8C,4H004 kg CH4 h−1.
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