Emissions, Topography, and Variation in XCO2 above the Southern California megacity

Abstract:

California’s South Coast Air Basin (SCB) (composed Orange and parts of Los Angeles, Riverside, and San Bernardino counties), is home to approximately 17 million people and accounts for about half a percent of global anthropogenic carbon emissions. The SCB has been a focus site of efforts to evaluate the ability of top-down methods to diagnose emissions from the world’s megacities using measurements of CO2 from both in situ and remote sensing. The topography within the SCB is, however, rather unique. Debris flow from the rapidly ascending San Gabriel Mountains that bound the north of the basin has produced sharp topographic relief with mean surface elevation sloping from the ocean at the southwest to nearly 500 m at the foothills of the mountains only 50 km to the northeast. Several valleys cut through the basin producing even more complex circulation. Using remote sensing observations of the total column mean CO2 mixing ratio (XCO2) made from ground-based spectrometers and from space (OCO-2) together with high-resolution WRF simulations coupled to the building-level Hestia-LA CO2 emission product, we examine how gradients in XCO2 are driven by both emissions and transport though the complex topographic tapestry of the SCB.