Search

NASA's Orbiting Carbon Observatories (OCO‐2 and OCO‐3) provide measurements of column‐averaged carbon dioxide concentrations (XCO2) with sufficient spatial resolution and precision to constrain bottom‐up estimates of CO2 fluxes at regional scales. We use Bayesian inversion methods assimilating satellite retrievals to improve estimates of CO2 fluxes in the South Coast Air Basin (SoCAB) which surrounds Los Angeles, and in the San Francisco Bay Area Air Basin (SFBA). We study 2020 to understand the impact of the COVID‐19 lockdowns and an active wildfire season. Our results indicated that a 50% (30%) reduction in CO2 emissions relative to 2015 during the COVID‐19 lockdown period was consistent with OCO measurements for SFBA (SoCAB). We find that posterior wildfire emissions differed significantly from the prior at the scale of individual wildfires, though with large uncertainties, and that wildfire emissions in SFBA are significant, attributing 72% of the region's CO2 emissions during August 2020 to wildfires. Plain Language Summary: Satellites can measure variations in carbon dioxide concentrations over urban areas. These measurements can be combined with models of the atmosphere to validate estimates of carbon dioxide emissions. We use this approach to better understand emissions in and around San Francisco and Los Angeles, the two major cities in California. We study the year 2020 to see how emissions changed in response to COVID‐19 lockdowns and to observe emissions from wildfires. The satellite measurements combined with the atmospheric model provide us with updated emission estimates that more closely match the measurements and provide greater certainty than our initial estimate of emissions. We also observe reduced emissions during lockdowns in both cities, updated emissions at the scale of individual wildfires, and large emissions from wildfires during peak wildfire season in the San Francisco Bay Area. Key Points: Satellite measurements can be used to validate emission inventories of CO2 within urban areas of CaliforniaChanges in CO2 emissions due to COVID‐19 lockdowns and wildfires in 2020 are captured by satellitesDuring August 2020, wildfires were responsible for 72% of CO2 emissions in the Bay Area [ABSTRACT FROM AUTHOR]