Abstract
Abstract. Satellite measurements of atmospheric trace gases have proved to be an invaluable tool for monitoring the Earth system. When these measurements are to be used for assessing tropospheric emissions and pollution, as for example in the case of nadir measurements of nitrogen dioxide (NO2), it is necessary to separate the stratospheric from the tropospheric signal. The SCIAMACHY instrument offers the unique opportunity to combine its measurements in limb- and nadir-viewing geometries into a tropospheric data product, using the limb measurements of the stratospheric NO2 abundances to correct the nadir measurements' total columns. In this manuscript, we present a novel approach to limb/nadir matching, calculating one stratospheric NO2 value from limb measurements for every single nadir measurement, abandoning global coverage for the sake of spatial accuracy. For comparison, modelled stratospheric NO2 columns from the Oslo CTM2 are also evaluated for stratospheric correction. Our study shows that stratospheric NO2 columns from SCIAMACHY limb measurements very well reflect stratospheric conditions. The zonal variability of the stratospheric NO2 field is captured by our matching algorithm, and the quality of the resulting tropospheric NO2 columns improves considerably. Both stratospheric datasets need to be adjusted to the level of the nadir measurements, because a time- and latitude-dependent bias to the measured nadir columns can be observed over clean regions. After this offset is removed, the two datasets agree remarkably well, and both stratospheric correction methods provide a significant improvement to the retrieval of tropospheric NO2 columns from the SCIAMACHY instrument.
Highlights
Hydrology and tunity to combine its measurements in limb- and nadirviewing geometries into a tropospheric data product, using the limb measurements of the stratospheric NO2 abundances to correct the nadir measurements’ total columns.In this manuscript, we present a novel approach to limb/nadir matching, calculating one stratospheric NO2 value from limb measurements for every single nadir measurement, abandoning global coverage for the sake of spatial accuracy
SCIAMACHY limb measurements and Oslo CTM2 simulations for the 2003–2007 time period, for the latitudes between 60◦ S and eral, our findings show that clouds cannot vertical column densities (VCD)
We implemented the direct limb/nadir matching method to correct for the stratospheric contribution to total slant columns of NO2 retrieved using the DOAS technique from SCIAMACHY nadir measurements
Summary
Hydrology and tunity to combine its measurements in limb- and nadirviewing geometries into a tropospheric data product, using the limb measurements of the stratospheric NO2 abundances to correct the nadir measurements’ total columns. In this manuscript, we present a novel approach to limb/nadir matching, calculating one stratospheric NO2 value from limb measurements for every single nadir measurement, abandoning global coverage for the sake of spatial accuracy. The zonal variability of the stratospheric NO2 field is captured by our matching algorithm, and the quality of the resulting tropospheric NO2 columns improves considerably Both stratospheric datasets need to be adjusted to the level of the nadir measurements, because a time- and latitude-dependent bias to the measured nadir columns can be observed over clean regions. Since the mid-1990s, the Global Ozone Monitoring Experiment (GOME, Burrows et al, 1999), the SCanning Imaging Absorption spectroMeter for Atmospheric 1999; BCuHrraorwtosgraepthYaOl.(,ScC1eI9Aa9M5n, ASCanHcdiYe,rneBfcoevreeenncsemsantnheerteianl).,, the Ozone Monitoring Instrument (OMI, Levelt et al., 2006), and GOME’s successor GOME-2 (Callies et al., 2000) have been launched in the class of nadir-viewing
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