Estimating methane and nitrous oxide emissions in California using multi-tower observations and hierarchical Bayesian inversion

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Seongeun Jeong1, Ying Hsu2, Sally Newman3, Jingsong Zhang4, Arlyn E Andrews5, Laura Bianco6, Justin Bagley1, Xinguang Cui1, Heather D Graven7, Jooil Kim8, Peter Salameh9, Brian W LaFranchi10, Chad Priest4, Mixtli Campos-Pineda4, Elena Novakovskaia11, Christopher Sloop12, Hope A Michelsen10, Ray Bambha10, Ray F Weiss13, Ralph F Keeling14 and Marc Laurenz Fischer15, (1)Lawrence Berkeley National Lab, Berkeley, CA, United States, (2)CAL/EPA (Air Resources Board), Sacramento, CA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)University of California, Riverside, Riverside, United States, (5)NOAA Earth System Research Lab, Boulder, CO, United States, (6)NOAA Boulder, Boulder, CO, United States, (7)Imperial College London, London, United Kingdom, (8)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (9)Scripps Institution of Oceanography, Carlsbad, CA, United States, (10)Sandia National Laboratories, Albuquerque, NM, United States, (11)George Mason University Fairfax, Fairfax, VA, United States, (12)Earth Networks Inc., Germantown, MD, United States, (13)Scripps Institution of Oceanography, La Jolla, CA, United States, (14)University of California San Diego, La Jolla, CA, United States, (15)Lawrence Berkeley National Laboratory, Berkeley, CA, United States
We present an analysis of annual state total methane (CH4) and nitrous oxide (N2O) emissions from California using atmospheric observations from thirteen sites (six sites for N2O) in California during June 2013 – May 2014. A hierarchical Bayesian inversion (HBI) method is used to estimate CH4 and N2O emissions for spatial regions (0.3 degree pixels) by comparing measured mixing ratios with transport model (WRF-STILT) predictions. Using the multi-site measurements across California, the HBI analysis constrains a significant portion of expected emissions for both CH4 and N2O in the Central Valley and southern California. Based on the HBI analysis, we estimate a likely range of the state’s annual CH4 emissions is 2.4 – 2.7 Tg CH4/yr (at 68% confidence), which is 1.4 - 1.6 times the total estimated by the California Air Resources Board (CARB). Similarly, we estimate the state’s annual N2O emissions to be 77 – 95 Gg N2O/yr (at 68% confidence), which are 1.6 – 2.0 times CARB’s state total. These results suggest that the combined total of CH4 and N2O emissions from the HBI analysis would comprise 18 – 21% of state total greenhouse gas (GHG) emissions, higher than 12% estimated in the current state inventory. Additionally, we expand previous evaluations of possible systematic bias in annual emission estimates due to transport model error by comparing measured and predicted carbon monoxide (CO) for four of the sites. These results highlight the need for multiple independent methods to estimate non-CO2 GHG emissions, and offer insight into opportunities for non-CO2 GHG emission mitigation efforts towards achieving California’s GHG emission goals.