Analysis of non-methane hydrocarbon data from a monitoring station affected by oil and gas development in the Eagle Ford shale, Texas

Abstract

Within the last decade, unconventional oil and gas exploration in the US has become a new source of atmospheric hydrocarbons. Although a geographically dispersed source, field measurements in and downwind of a number of shale basins demonstrate the impact exploration activities have on ambient levels of hydrocarbons. Due to concerns related to ozone production, regulatory agencies are adding monitoring stations to better understand the potential influence of emissions from areas with increased oil and gas related activities. The Eagle Ford shale in south Texas is a rapidly developing shale play producing both oil and natural gas, providing 10% and 5% of US domestic oil and gas production, respectively, in 2013. We analyzed the first year of measurements from a newly established monitoring site at its central north edge. The data reveal median ethane mixing ratios-used as a marker for oil and gas exploration related emissions-at five times its typical clean air background. Ethane mixing ratios above ten times the background occurred regularly. Saturated hydrocarbons with likely origin in oil and gas exploration explain half of the data set's variability. They dominate OH radical reactivity at levels both similar to other shale areas and similar to Houston's ship channel area a decade ago. Air advecting slowly across the shale area from east-southeast and southwest directions shows the most elevated hydrocarbon concentrations, and evidence is presented linking elevated alkene abundances to flaring in the shale area. A case study is presented linking high emissions from an upwind facility to hydrocarbon plumes observed at the monitor.

Source apportionment of non-methane hydrocarbons, NOx and H2S data from a central monitoring station in the Eagle Ford shale, Texas

“…Both of these aspects are more relevant in oil producing shale areas, such as the Eagle Ford shale in Texas, as compared to mostly gas producing shale areas, such as the Marcellus shale. This is because in the latter, the dominant hydrocarbon emissions consist of methane and ethane (Vinciguerra et al, 2015), which have low atmospheric reactivity, while a suite of NMHCs is emitted in the former areas (Helmig et al, 2014;Schade and Roest, 2016). In addition, flaring in oil producing shale areas (Elvidge et al, 2016) is a significant source of NO x (AACOG Natural Resources Department, 2014), but flaring is rare in gas producing shale areas.…”

“…VOC measurements at the Karnes City site are performed in the same manner as at TCEQ's Floresville monitoring site (Figure 1; Schade and Roest, 2016) at the northern edge of the shale area. TCEQ's Standard Operating Procedure for VOC precursor analysis (TCEQ, 2005) is available through their Field Operations Division.…”

“…TCEQ's Standard Operating Procedure for VOC precursor analysis (TCEQ, 2005) is available through their Field Operations Division. As summarized previously (Schade and Roest, 2016), an automated GC dual FID system is used to hourly process a 40 min, 600 mL volume gas sample trapped onto a cooled adsorbent, rapidly thermally desorbed onto two chromatographic columns separating short-chained and long-chained NMHCs, respectively. Here, we reiterate two features of this widely deployed NMHCs analysis system in Texas: (i) the use of a Nafion™ dryer to remove water vapor from the sample stream, and (ii) the lack of ozone removal from the air sample before preconcentration.…”

“…the exploration of oil and gas from shales using horizontal drilling, slickwater mixtures, and hydraulic fracturing, is a relatively new source of air pollutants to the lower atmosphere. The rapid development of UOG in several United States shale areas has not only increased domestic oil and gas production (Energy Information Administration, 2015), but has also caused an increase in methane and nonmethane hydrocarbon (NMHC) emissions to the atmosphere (Petron et al, 2012;Gilman et al, 2013;Karion et al, 2013;LaFranchi et al, 2013;Miller et al, 2013;Peischl et al, 2013;Swarthout et al, 2013;Edwards et al, 2014;Helmig et al, 2014;Macey et al, 2014;Petron et al, 2014;Thompson et al, 2014;Zavala-Araiza et al, 2014;Karion et al, 2015;Lan et al, 2015;Lavoie et al, 2015;Smith et al, 2015;Townsend-Small et al, 2015;Yacovitch et al, 2015;Yuan et al, 2015;Zavala-Araiza et al, 2015a;Zavala-Araiza et al, 2015b;Zimmerle et al, 2015;Allen, 2016;Eisele et al, 2016;Franco et al, 2016;Helmig et al, 2016;Kort et al, 2016;Lyon et al, 2016;Marrero et al, 2016;Olaguer et al, 2016;Prenni et al, 2016;Schade and Roest, 2016;Turner et al, 2016).…”

Quantifying alkane emissions in the Eagle Ford Shale using boundary layer enhancement

“…Alkanes dominate atmospheric OH radical reactivity at a TCEQ monitoring site north of the EFS (Schade and Roest, 2016) and the emission estimates for these short-chain alkanes are needed to assess the potential air quality impacts from the EFS. We focus on ethane as a tracer for oil and gas emissions as it is the second-most abundant compound in natural gas (Xiao et al, 2008) and, unlike methane, it is not emitted by microbial sources in significant quantities (Simpson et al, 2012).…”