Quantifying Emissions of CO and NO _x Using Observations From MOPITT, OMI, TES, and OSIRIS

We use the GEOS-Chem four-dimensional variational data assimilation system to estimate emissions of carbon monoxide (CO) and nitrogen oxides (NO _x ) in November 2009 and July 2010. We assimilated CO retrievals from The Measurements of Pollution In The Troposphere (MOPITT), ozone (O ₃ ) retrievals from the Tropospheric Emission Spectrometer (TES) and the Optical Spectrograph and InfraRed Imager System (OSIRIS), and NO ₂ columns from the Ozone Monitoring Instrument (OMI). By assimilating data for multiple chemical species with the four-dimensional variational scheme we obtain a consistent chemical state over the assimilation period. The modeled O ₃ bias was reduced to less than 3.5 ppbv everywhere, relative to independent aircraft O ₃ data, except in the high-latitude upper troposphere and lower stratosphere. We found that in November, the CO and NO _x emission estimates obtained with the multiple species assimilation were generally comparable to those inferred from assimilating only MOPITT or OMI data, respectively, whereas in July the differences were larger. For the main anthropogenic source regions, the inferred North American and European emissions responded most strongly to the multispecies information in the assimilation. In July, North American and European CO emission estimates differed by 31% and 65% relative to the MOPITT-only estimates, respectively. We also found large differences for the North American and European NO _x emission estimates, which differed by 27% and 16% relative to the OMI-only estimates, respectively. Our results highlight the potential benefit of exploiting the additional constraints offered by multispecies chemical data assimilation.