Atmospheric and air quality implications of C2-C5 alkane emissions from the oil and gas sector
Date
2018
Authors
Tzompa Sosa, Zitely Asafay, author
Fischer, Emily, advisor
Kreidenweis, Sonia M., committee member
Pierce, Jeffrey, committee member
Jathar, Shantanu, committee member
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Abstract
Emissions of C2-C5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. This dissertation quantifies the role of the oil and gas sector on light alkane emissions and abundances at local, regional, and global scales. First, we present an updated global ethane (C2H6) emission inventory based on 2010 satellite-derived CH4 fluxes with adjusted C2H6 emissions over the U.S. from the National Emission Inventory (NEI 2011). We contrast our global 2010 C2H6 emission inventory with one developed for 2001. The C2H6 difference between global anthropogenic emissions is subtle (7.9 versus 7.2 Tg yr-1), but the spatial distribution of the emissions is distinct. In the 2010 C2H6 inventory, fossil fuel sources in the Northern Hemisphere represent half of global C2H6 emissions and 95% of global fossil fuel emissions. Over the U.S., un-adjusted NEI 2011 C2H6 emissions produce mixing ratios that are 14-50 % of those observed by aircraft observations (2008-2014). When the NEI 2011 C2H6 emission totals are scaled by a factor of 1.4, the GEOS-Chem model largely reproduces a regional suite of observations, with the exception of the central U.S., where it continues to under- predict observed mixing ratios in the lower troposphere. Second, we use a nested GEOS-Chem simulation driven by updated 2011NEI emissions with aircraft, surface and column observations to 1) document spatial patterns in the emissions and observed atmospheric abundances of C2-C5 alkanes over the U.S., 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 >80% of the total U.S. emissions of C2H6 and propane (C3H8), and emissions of these species are largest in the central U.S. Observed mixing ratios of C2-C5 alkanes show enhancements over the central U.S. 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 U.S., 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 ≤ C6 alkanes are sufficient to understand air quality issues in regions with large emissions of these species. Finally, we investigate the contribution of C2-C5 alkane emissions from the U.S. oil and gas industry to O3 abundances at regional and global scales. Emissions of C2-C5 alkanes from the oil and gas sector make the largest contribution to ozone (O3) production over the central U.S. compared to other regions. The Colorado Front Range is the 8-hour O3 non-attainment area with the highest summertime daytime average O3 enhancement attributed to the U.S. oil and gas sector. The global tropospheric contribution of C2-C5 alkane emissions from the U.S. oil and gas sector to the O3 burden is 0.5 Tg for the year 2011, which represents 0.27% of the Northern Hemisphere tropospheric O3 burden.
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Rights Access
Subject
atmospheric impacts
oil and gas
propane
ethane
alkanes
ozone