Combing OMI and MLS to Improve Tropospheric Ozone Retrievals for Air Quality Applications

OMI and MLS, both measuring ozone profiles, are two of the four instruments on board the EOS AURA satellite. MLS measures ozone profiles at a vertical resolution of about 3 km from 0.1 mb to 200 mb but with a limited spatial coverage. OMI measures ozone profiles from the stratosphere to the troposphere at very high spatial resolution but with a much coarser vertical resolution especially in the troposphere. So combing MLS and OMI data can improve the separation of stratospheric ozone from tropospheric ozone. In this study, we first use zonal MLS data combined with climatological ozone profiles in the troposphere to correct for across-track dependent biases (-2%-5%) in OMI level 1b radiance. We then use MLS data as a priori information in the stratosphere to retrieve ozone profiles from corrected OMI radiances using the optimal estimation technique. The combined retrievals are compared MLS retrievals and OMI retrievals that do not use MLS information. The inclusion of MLS data in OMI retrievals reduces the uncertainty in both stratospheric column ozone and tropospheric column ozone compared to using either instrument alone and improves the identification of tropospheric ozone due to pollution.