Tropospheric ozone determined from Aura OMI and MLS: Evaluation of measurements and comparison with the Global Modeling Initiative’s Chemical Transport Model

Ozone measurements from the OMI and MLS instruments onboard the Aura satellite
are used for deriving global distributions of tropospheric column ozone (TCO). TCO is
determined using the tropospheric ozone residual method which involves subtracting
measurements of MLS stratospheric column ozone (SCO) from OMI total column ozone after
adjusting for inter-calibration differences of the two instruments using the convective-cloud
differential method. The derived TCO field, which covers one complete year of mostly
continuous daily measurements from late August 2004 through August 2005, is used for studying
the regional and global pollution on a time scale of a few days to months. The seasonal and
zonal characteristics of the observed TCO fields are also compared with TCO fields derived from
the Global Modeling Initiative’s Chemical Transport Model. The model and observations show
interesting similarities with respect to zonal and seasonal variations. However, there are notable
differences, particularly over the vast region of the Saharan desert.