Fig. 1: Seasonal cycles of excess ratio and CH4 emissions.
From: Decadal decrease in Los Angeles methane emissions is much smaller than bottom-up estimates
a Monthly ratio of excess XCH4 to excess XCO2, i.e. XCH4,xs/XCO2,xs, from 2011 to 2020 calculated from CLARS-FTS observations. Data for September 2020 are not available due to instrument shutdown during wildfires. As a comparison, the corresponding excess ratios derived using NOAA’s Mt. Wilson Observatory (MWO) flask measurements averaged over 2011–2020 are shown in black; (b) Monthly CH4 emissions in the LA basin from 2011 to 2020 are estimated based on the CO2 emissions from ODIAC and the derived monthly XCH4,xs/XCO2,ff excess ratio after correcting for the biogenic flux contribution. The error bars represent the estimation uncertainty (1σ) of the monthly values.
