Seasonality of biases between CMAQ and OMI tropospheric NO2 columns over the eastern and central U.S

We examine seasonal variations in biases between tropospheric NO2 columns from a regional chemical model (CMAQ) and the Ozone Monitoring Instrument (OMI) over the central and eastern U.S. The CMAQ columns are compared to OMI columns that were determined using a CMAQ-based air mass factor (AMF) as opposed to the climatological AMF that is in the standard product. This approach takes advantage of the higher spatial resolution of CMAQ. In general, the adjusted OMI columns are greater than the standard product. With US 2000 population data, we investigate Urban/Rural NO2 columns under different population thresholds. For 2006 we obtain similar results to other studies: CMAQ over-predicts in urban regions and underestimates in rural regions with percent biases largest during the summer. CMAQ has more high-bias regions than low-bias over all seasons, compared to either OMI standard or OMI adjusted columns. It also shows smaller model biases between CMAQ and OMI adjusted than the OMI standard product, with largest decreases in urban summer. In summary, we apply an adjustment to OMI standard tropospheric NO2 column taking account of regional CMAQ model profiles and compare the model column amounts with the OMI data. We will study the seasonal changes in tropospheric NO2 columns and CMAQ biases during the 2005 to 2008 time period.