Atmospheric Implications of Large C₂‐C₅ Alkane Emissions From the U.S. Oil and Gas Industry

Abstract

Emissions of C2‐C5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. We use a nested GEOS‐Chem simulation driven by updated 2011NEI emissions with aircraft, surface, and column observations to (1) examine spatial patterns in the emissions and observed atmospheric abundances of C2‐C5 alkanes over the United States and (2) estimate the contribution of emissions from the U.S. oil and gas industry to these patterns. The oil and gas sector in the updated 2011NEI contributes over 80% of the total U.S. emissions of ethane (C2H6) and propane (C3H8), and emissions of these species are largest in the central United States. Observed mixing ratios of C2‐C5 alkanes show enhancements over the central United States below 2 km. A nested GEOS‐Chem simulation underpredicts observed C3H8 mixing ratios in the boundary layer over several U.S. regions, and the relative underprediction is not consistent, suggesting C3H8 emissions should receive more attention moving forward. Our decision to consider only C4‐C5 alkane emissions as a single lumped species produces a geographic distribution similar to observations. Due to the increasing importance of oil and gas emissions in the United States, we recommend continued support of existing long‐term measurements of C2‐C5 alkanes. We suggest additional monitoring of C2‐C5 alkanes downwind of northeastern Colorado, Wyoming, and western North Dakota to capture changes in these regions. The atmospheric chemistry modeling community should also evaluate whether chemical mechanisms that lump larger alkanes are sufficient to understand air quality issues in regions with large emissions of these species.

Seasonality and Source Apportionment of Nonmethane Volatile Organic Compounds at Boulder Reservoir, Colorado, Between 2017 and 2019

“…Franco et al., 2016; Helmig et al., 2016), thus comparing data from Boulder Reservoir to older data needs to be done in this context. However, it is clear that propane abundances in the NRFMA are largely higher than many other U.S. areas (Tzompa‐Sosa et al., 2019), with some notable exceptions including the Marcellus Shale natural gas producing region (Swarthout et al., 2015).…”

Impacts of Emissions of C2‐C5 Alkanes From the U.S. Oil and Gas Sector on Ozone and Other Secondary Species

“…We estimate the contribution of C 2 ‐C 5 alkane emissions from the oil and gas sector to the hemispheric O 3 burden using two 2° × 2.5° global simulations (baseline and OG‐off). Tzompa‐Sosa et al (2019) estimated that the oil and gas industry is the largest anthropogenic source of C 2 H 6 (90%) and C 3 H 8 (84%), and this sector is the third largest source for C 4 ‐C 5 alkanes (26%) in the United States. The global tropospheric contribution of C 2 ‐C 5 alkane emissions from the U.S. oil and gas sector to the O 3 burden is 0.5 Tg for the year 2011, which represents 0.17% of the global tropospheric O 3 burden.…”

“…Our simulations use GEOS‐Chem model version 10‐01 (Bey et al, 2001) driven by off‐line GEOS‐5 assimilated meteorological fields with 47 vertical levels. The U.S. anthropogenic emissions correspond to a model‐ready version of the 2011 NEI (National Emission Inventory) that is part of the EPA 2011v6.3 emissions modeling platform (U.S. EPA, 2016; https://www.epa.gov/air-emissions-modeling/2011-version-63-technical-support-document), which was modified and implemented into GEOS‐Chem by Tzompa‐Sosa et al (2019). NO x (NO x = NO + NO 2 ) emission fluxes correspond to a total of 3.7 Tg N (nitrogen) for the year 2011.…”

“…U.S. total emissions of C 4 ‐C 5 alkanes are estimated as 36% of the total paraffin emissions. A detailed description of this calculation can be found in Tzompa‐Sosa et al (2019). Figures S1–S4 show the changes in spatial distribution of NO and C 4 ‐C 5 alkanes emissions.…”

“…Gilman et al, 2013; Goetz et al, 2017; Helmig et al, 2014; Katzenstein et al, 2003; Pétron et al, 2012; Thompson et al, 2014; Warneke et al, 2014). Emissions of C 2 ‐C 5 alkanes from the oil and gas sector have resulted in enhanced abundances of these species throughout the Northern Hemisphere troposphere with particularly large enhancements over the central and eastern United States (Tzompa‐Sosa et al, 2019). However, despite the high emission rates of C 2 ‐C 5 alkanes, relatively few studies have examined the contribution of these species to ozone (O 3 ) production at the surface (Edwards et al, 2013; Field et al, 2015; Helmig et al, 2016; Kort et al, 2016; McDuffie et al, 2016; Rappenglück et al, 2014; Tan, 2012).…”