Long-term tropospheric ozone from SCIAMACHY+OMPS and effects of the upper limit definition of the column

About 10% of the total amount of ozone resides in the troposphere, which acts as a potent greenhouse gas. Anthropogenic emissions and biomass burning are the main sources of ozone in the troposphere, and overexposure to this pollutant causes health problems and damages vegetation.

A combination of space-borne limb and nadir measurements in the UV-visible spectral range (so-called limb-nadir matching, LNM) provides valuable information on tropospheric ozone. This study uses data from the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) (2002-2012) and Ozone Mapping and Profiler Suite on board of Suomi National Polar-Orbiting Partnership (OMPS/NPP, since 2012). Both instruments observe the atmosphere in both limb and nadir geometry. Tropospheric ozone columns are retrieved globally by subtracting the stratospheric ozone column calculated from limb observations from the total ozone column derived from the nadir measurements.

Tropospheric ozone retrievals use different upper altitude limits to calculate the tropospheric ozone column. In the case of the LNM technique, the upper limit is defined by the thermal and/or dynamical tropopause. The Convective Clouds Differential technique (CCD) calculates the tropospheric ozone column up to 270 hPa. Phase II of the Tropospheric Ozone Assessment Report (TOAR-II) uses different pressure levels for different latitudes as an upper limit for the tropospheric column.

After updating and improving the SCIAMACHY-LNM and the OMPS/NPP-LNM datasets, we obtained a long-term dataset of tropospheric ozone (2002-2023) by merging them. Here, we present this new long-term LNM tropospheric ozone column dataset, which has been converted to the different definitions of column heights as prescribed in TOAR II. The datasets are validated using ozonesondes, and the results for the different column definitions are evaluated and discussed.