Resolving Urban to Rural CH4 Emissions Across California with Multi-site Observations

Methane emissions are included in California's commitment (Assembly Bill 32) to return total greenhouse gas emissions to 1990 levels by 2020. We will present atmospheric inversion estimates of California's total CH4 emissions for summer 2012, using data from more than a dozen tower sites covering urban and rural areas of California's South Coast Air Basin, Central Valley, San Francisco Bay Area, and North Coast. We use Bayesian inversions to estimate the CH4 emissions from discrete regions of California by combining the local measurements, background CH4 , two 0.1 degree prior model emission maps (one specific to California and one global), and predicted atmospheric transport from WRF-STILT. We quantify site-specific model-measurement uncertainties due to transport using meteorological data from a network of atmospheric profilers and in-situ sensors, due to background using oceanic and aircraft observations, and the prior emissions using the spread results obtained with the two different maps and a prior-free model. We expect the results of this study will significantly improve upon existing work in providing a regionally specific separation of emission from the urban and rural CH4 sources.