A spring time case study of tropospheric ozone column enhancements over North America using a regional model and satellite data

We examine the variability of tropospheric ozone columns (TCOs) using a regional 3-D chemical transport model, the Tropospheric Emission Spectrometer (TES) measurements and the Aura derived tropospheric ozone residuals (TORs) for spring 2005. 2D interpolation and PV/Geopotential height mapping techniques have been applied to MLS profiles to derive the Ozone Monitoring Instrument (OMI)/MLS tropospheric column residuals. Two six-day periods in March have been selected to study the periodic TCO enhancements in two regions, one centered around the Baja peninsula (Mexico) and the west coast of California, the other centered around Florida. Thirteen day back trajectories and daily maps of carbon monoxide (CO) and ozone from GEOS-CHEM have been integrated to investigate the influence of cross-pacific transport on the high tropospheric ozone columns in the first region. Meteorological fields indicate that the high TCO values centered over California, Mexico are associated with strong and deep sinking motion. The correlation between TCO values and the surface ozone from EPA ground network measurements are used to investigate possible TCO enhancements in this region associated with the increase of the surface ozone. Correlations with geopotential height and wind fields, however, suggest that the high ozone at this time over the southeastern USA is more likely to be associated with the advection of ozone from high TCO areas and not with local surface ozone enhancement.