Source Partitioning of Methane Emissions and its Seasonality in the U.S. Midwest. Issue 2 (28th February 2018)

• Record Type: Journal Article
• Authors: Chen, Zichong; Griffis, Timothy J.; Baker, John M.; Millet, Dylan B.; Wood, Jeffrey D.; Dlugokencky, Edward J.; Andrews, Arlyn E.; Sweeney, Colm; Hu, Cheng; Kolka, Randall K.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 2(2018)
• Page Start: 646
• Page End: 659
• Publication Date: 2018-02-28
• Subjects: methane source partitioning -- Bayesian inversion -- aerodynamic flux -- wetland emissions; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1002/2017JG004356
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: The methane (CH4 ) budget and its source partitioning are poorly constrained in the Midwestern United States. We used tall tower (185 m) aerodynamic flux measurements and atmospheric scale factor Bayesian inversions to constrain the monthly budget and to partition the total budget into natural (e.g., wetlands) and anthropogenic (e.g., livestock, waste, and natural gas) sources for the period June 2016 to September 2017. Aerodynamic flux observations indicated that the landscape was a CH4 source with a mean annual CH4 flux of +13.7 ± 0.34 nmol m −2 s −1 and was rarely a net sink. The scale factor Bayesian inversion analyses revealed a mean annual source of +12.3 ± 2.1 nmol m −2 s −1 . Flux partitioning revealed that the anthropogenic source (7.8 ± 1.6 Tg CH4 yr −1 ) was 1.5 times greater than the bottom‐up gridded United States Environmental Protection Agency inventory, in which livestock and oil/gas sources were underestimated by 1.8‐fold and 1.3‐fold, respectively. Wetland emissions (4.0 ± 1.2 Tg CH4 yr −1 ) were the second largest source, accounting for 34% of the total budget. The temporal variability of total CH4 emissions was dominated by wetlands with peak emissions occurring in August. In contrast, emissions from oil/gas and other anthropogenic sources showed relatively weak seasonality. Key Points: The optimized total anthropogenic emissions were 1.5× higher than the a priori bottom‐up inventory estimates Livestock and wetland sources represented 41% and 34% of total methane emissions, respectively The temporal variability of the regional emissions was dominated by wetlands with peak emissions occurring in August