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Published May 16, 2019 | Published
Journal Article Open

Spatio-temporally Resolved Methane Fluxes From the Los Angeles Megacity


We combine sustained observations from a network of atmospheric monitoring stations with inverse modeling to uniquely obtain spatiotemporal (3‐km, 4‐day) estimates of methane emissions from the Los Angeles megacity and the broader South Coast Air Basin for 2015–2016. Our inversions use customized and validated high‐fidelity meteorological output from Weather Research Forecasting and Stochastic Time‐Inverted Lagrangian model for South Coast Air Basin and innovatively employ a model resolution matrix‐based metric to disentangle the spatiotemporal information content of observations as manifested through estimated fluxes. We partially track and constrain fluxes from the Aliso Canyon natural gas leak and detect closure of the Puente Hills landfill, with no prior information. Our annually aggregated fluxes and their uncertainty excluding the Aliso Canyon leak period lie within the uncertainty bounds of the fluxes reported by the previous studies. Spatially, major sources of CH_4 emissions in the basin were correlated with CH_4‐emitting infrastructure. Temporally, our findings show large seasonal variations in CH_4 fluxes with significantly higher fluxes in winter in comparison to summer months, which is consistent with natural gas demand and anticorrelated with air temperature. Overall, this is the first study that utilizes inversions to detect both enhancement (Aliso Canyon leak) and reduction (Puente Hills) in CH_4 fluxes due to the unintended events and policy decisions and thereby demonstrates the utility of inverse modeling for identifying variations in fluxes at fine spatiotemporal resolution.

Additional Information

Published 2019. This article is a U.S. Government work and is in the public domain in the USA. Received 1 DEC 2018; Accepted 29 MAR 2019; Accepted article online 8 APR 2019; Published online 13 MAY 2019. A portion of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). Additional support was provided by the National Institute of Standards and Technology (NIST) Greenhouse Gas and Climate Science Measurements program. Measurements at SBC were supported by the California Air Resourced Board project (11‐306) at LBNL, operating under U.S. Department of Energy (DOE) contract DE‐AC02‐05CH11231. The authors also acknowledge support from NASA's Carbon Monitoring System program and the Prototype Methane Monitoring System for California project. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. The views expressed in this article are those of the authors and do not represent the views or policies of the California Air Resources Board.

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