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Estimating methane emissions in California's urban and rural regions using multitower observations
Author(s) -
Jeong Seongeun,
Newman Sally,
Zhang Jingsong,
Andrews Arlyn E.,
Bianco Laura,
Bagley Justin,
Cui Xinguang,
Graven Heather,
Kim Jooil,
Salameh Peter,
LaFranchi Brian W.,
Priest Chad,
CamposPineda Mixtli,
Novakovskaia Elena,
Sloop Christopher D.,
Michelsen Hope A.,
Bambha Ray P.,
Weiss Ray F.,
Keeling Ralph,
Fischer Marc L.
Publication year - 2016
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd025404
Subject(s) - environmental science , emission inventory , methane emissions , atmospheric sciences , methane , trace gas , greenhouse gas , climatology , meteorology , air quality index , geography , geology , chemistry , oceanography , organic chemistry
We present an analysis of methane (CH 4 ) emissions using atmospheric observations from 13 sites in California during June 2013 to May 2014. A hierarchical Bayesian inversion method is used to estimate CH 4 emissions for spatial regions (0.3° pixels for major regions) by comparing measured CH 4 mixing ratios with transport model (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) predictions based on seasonally varying California‐specific CH 4 prior emission models. The transport model is assessed using a combination of meteorological and carbon monoxide (CO) measurements coupled with the gridded California Air Resources Board (CARB) CO emission inventory. The hierarchical Bayesian inversion suggests that state annual anthropogenic CH 4 emissions are 2.42 ± 0.49 Tg CH 4 /yr (at 95% confidence), higher (1.2–1.8 times) than the current CARB inventory (1.64 Tg CH 4 /yr in 2013). It should be noted that undiagnosed sources of errors or uncaptured errors in the model‐measurement mismatch covariance may increase these uncertainty bounds beyond that indicated here. The CH 4 emissions from the Central Valley and urban regions (San Francisco Bay and South Coast Air Basins) account for ~58% and 26% of the total posterior emissions, respectively. This study suggests that the livestock sector is likely the major contributor to the state total CH 4 emissions, in agreement with CARB's inventory. Attribution to source sectors for subregions of California using additional trace gas species would further improve the quantification of California's CH 4 emissions and mitigation efforts toward the California Global Warming Solutions Act of 2006 (Assembly Bill 32).