Validation and Interpretation of OMI Tropospheric NO2 Observations During INTEX- B

Abstract

We present first results from an intercomparison of OMI tropospheric NO2 columns with collocated NO2 profiles measured on board the DC8 aircraft during the first phase of the INTEX-B campaign in March 2006. We find that cloud-free OMI and DC8 tropospheric NO2 columns observed over scenes ranging from strongly polluted (Mexican mainland, Houston) to remote (Gulf of Mexico) are highly consistent, with OMI columns showing no significant bias relative to the independent aircraft measurements. We interpret our results using the GEOS-Chem chemistry-transport model with improved emissions for Northern Mexico. For the first time, we use the OMI NO2 data to check national best estimates of bottom- up emissions from NEI99 (USA) and BRAVO (Mexico). We find that NEI99 emissions over the United States are 30% too high to properly simulate the OMI observations. Furthermore, we present comparisons between NO2 simulations from the high-resolution (12 x 12 km2) regional chemical-transport model CMAQ and OMI observed NO2 (13 x 24 km2) over the Houston area to investigate to what extent the spatial resolution of emissions can be usefully constrained with OMI data.