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Title: Top-down methane emissions estimates for the San Francisco Bay Area from 1990 to 2012

Methane is a potent greenhouse gas (GHG) that is now included in both California State and San Francisco Bay Area (SFBA) bottom-up emission inventories as part of California's effort to reduce anthropogenic GHG emissions. Here we provide a top-down estimate of methane (CH 4) emissions from the SFBA by combining atmospheric measurements with the comparatively better estimated emission inventory for carbon monoxide (CO). Local enhancements of CH 4 and CO are estimated using measurements from 14 air quality sites in the SFBA combined together with global background measurements. Mean annual CH 4 emissions are estimated from the product of Bay Area Air Quality Management District (BAAQMD) emission inventory CO and the slope of ambient local CH 4 to CO. The resulting top-down estimates of CH 4 emissions are found to decrease slightly from 1990 to 2012, with a mean value of 240 ± 60 GgCH 4 yr⁻¹ (at 95% confidence) in the most recent (2009–2012) period, and correspond to reasonably a constant factor of 1.5–2.0 (at 95% confidence) times larger than the BAAQMD CH 4 emission inventory. However, we note that uncertainty in these emission estimates is dominated by the variation in CH 4:CO enhancement ratios across the observing sitesmore » and we expect the estimates could represent a lower-limit on CH 4 emissions because BAAQMD monitoring sites focus on urban air quality and may be biased toward CO rather than CH 4 sources.« less
Authors:
ORCiD logo [1] ;  [2]
  1. Bay Area Quality Management District, San Francisco, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Atmospheric Environment (1994)
Additional Journal Information:
Journal Name: Atmospheric Environment (1994); Journal Volume: 107; Journal Issue: C; Journal ID: ISSN 1352-2310
Publisher:
Elsevier
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; methane emissions; emissions inventory; greenhouse gas; inventory verification; top-down estimates
OSTI Identifier:
1208641