SO^sub 2^ emissions and lifetimes: Estimates from inverse modeling using in situ and global, space-based (SCIAMACHY and OMI) observations

Top-down constraints on global sulfur dioxide (SO2) emissions are inferred through inverse modeling using SO2 column observations from two satellite instruments (SCIAMACHY and OMI). The authors first evaluated the SO2 column observations with surface SO2 measurements by applying local scaling factors from a global chemical transport model (GEOS-Chem) to SO2 columns retrieved from the satellite instruments. The resulting annual mean surface SO2 mixing ratios for 2006 exhibit a significant spatial correlation with coincident in situ measurements from monitoring networks throughout the US and Canada. The author evaluate the GEOS-Chem simulation of the SO2 lifetime with that inferred from in situ measurements to verify the applicability of GEOS-Chem for inversion of SO2 columns to emissions. Their global estimate for annual land surface anthropogenic SO2 emissions closely agrees with the bottom-up emissions in the GEOS-Chem model and exhibits consistency in global distributions with the bottom-up emissions. However, there are significant regional differences.