Estimating Emission Ratios of Nitrogen Dioxide, Carbon Monoxide and Carbon Dioxide using Satellite Observations

Abstract:

Enhancement ratios of atmospheric trace gases in a pollution plume provide information on the plume composition and the underlying emissions. These enhancement ratios between atmospheric constituents can be calculated using measurements taken downwind of sources of air pollutants and greenhouse gases. We apply this technique to 25 large cities around the world using co-located measurements from three satellite instruments: the Orbiting Carbon Observatory-2 (OCO-2), the Orbiting Carbon Observatory-3 (OCO-3) onboard the International Space Station (ISS) and the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 Precursor (S5P). From these satellite measurements, we calculate NO2:CO, NO2:CO2 and CO:CO2 enhancement ratios and compare them with emission ratios from several global inventories, including the Emissions Database for Global Atmospheric Research (EDGAR), MACC/CityZEN (MACCity), the Fossil Fuel Data Assimilation System (FFDAS), and the Open-source Data Inventory for Anthropogenic CO2 (ODIAC). Initial results of ratios derived from satellite measurements were found to be in good agreement with previous studies measuring CO:CO2 ratios in California's South Coast Air Basin and with other studies which use TROPOMI observations to measure NO2:CO ratios. In the North American and European cities we studied, we find enhancement ratios of NO2:CO are significantly lower than those derived using fluxes from the EDGAR and MACCity global emissions inventories. Comparisons with the calculated NO2:CO2 and CO:CO2 ratios suggest that these global inventories may underestimate emissions of CO and that EDGAR may overestimate emissions of NO2 in the North American and European cities that were investigated.