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Methane Emissions From the Baltimore‐Washington Area Based on Airborne Observations: Comparison to Emissions Inventories
Author(s) -
Ren Xinrong,
Salmon Olivia E.,
Hansford Jonathan R.,
Ahn Doyeon,
Hall Dolly,
Benish Sarah E.,
Stratton Phillip R.,
He Hao,
Sahu Sayantan,
Grimes Courtney,
Heimburger Alexie M. F.,
Martin Cory R.,
Cohen Mark D.,
Stunder Barbara,
Salawitch Ross J.,
Ehrman Sheryl H.,
Shepson Paul B.,
Dickerson Russell R.
Publication year - 2018
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd028851
Subject(s) - greenhouse gas , environmental science , methane , emission inventory , radiative forcing , atmospheric sciences , carbon dioxide , population , carbon fibers , air quality index , meteorology , chemistry , geography , aerosol , ecology , demography , organic chemistry , sociology , geology , biology , materials science , composite number , composite material
Urban areas are responsible for a substantial fraction of anthropogenic emissions of greenhouse gases (GHGs) including methane (CH 4 ), with the second largest anthropogenic direct radiative forcing relative to carbon dioxide (CO 2 ). Quantification of urban CH 4 emissions is important for establishing GHG mitigation policies. Comparison of observation‐based and inventory‐based urban CH 4 emissions suggests possible improvements in estimating CH 4 source emissions in urban environments. In this study, we quantify CH 4 emissions from the Baltimore‐Washington area based on the mass balance aircraft flight experiments conducted in Winters 2015 and 2016. The field measurement‐based mean winter CH 4 emission rates from this area were 8.66 ± 4.17 kg/s in 2015 and 9.14 ± 4.49 kg/s in 2016, which are 2.8 times the 2012 average U.S. GHG Inventory‐based emission rate. The observed emission rate is 1.7 times that given in a population‐apportioned state of Maryland inventory. Methane emission rates inferred from carbon monoxide (CO) and CO 2 emission inventories and observed CH 4 /CO and CH 4 /CO 2 enhancement ratios are similar to those from the mass balance approach. The observed ethane‐to‐methane ratios, with a mean value of 3.3% in Winter 2015 and 4.3% in Winter 2016, indicate that the urban natural gas system could be responsible for ~40–60% of total CH 4 emissions from this area. Landfills also appear to be a major contributor, providing 25 ± 15% of the total emissions for the region. Our study suggests there are grounds to reexamine the CH 4 emissions estimates for the Baltimore‐Washington area and to conduct flights in other seasons.