Tropospheric trace gas retrievals from TROPOMI/Sentinel-5P

Abstract

This presentation focuses on tropospheric NO2 and ozone products from TROPOMI/Sentinel-5P as developed at the Remote Sensing Technology institute of the German Aerospace Center (DLR). We present an overview of the retrieval algorithms and show examples of air quality applications. The retrieval of tropospheric NO2 columns from TROPOMI uses an Differential Optical Absorption Spectroscopy (DOAS) algorithm with air mass factor conversions calculated using the LIDORT model. First, total NO2 slant column densities are determined using the DOAS method in the visible wavelength region (405-465 nm). Then the STRatospheric Estimation Algorithm from Mainz (STREAM) is applied to separate the stratospheric and tropospheric contribution. Finally, the tropospheric slant column is converted into a vertical column using a tropospheric AMF based on a priori NO2 profiles from the TM5-MP chemistry transport model. A cloud correction is applied based on TROPOMI cloud properties as derived by the OCRA and ROCINN algorithms. The tropospheric ozone columns are derived from total columns from TROPOMI and stratospheric columns based on 4D-Var assimilation of Aura MLS ozone profiles. The total ozone columns are determined from TROPOMI with a two step DOAS approach, consisting of a slant column retrieval in the UV wavelength region around 330 nm, and an iterative AMF-calculation using the LIDORT model. MLS profiles are assimilated by the Belgian Assimilation System for Chemical ObsErvations (BASCOE) and are delivered with a time frequency of 3 hours. BASCOE stratospheric columns are interpolated linearly in time and space to TROPOMI total column locations before subtraction. To avoid potential errors we only use cloud free TROPOMI data. The use of one and a half year of Sentinel-5P measurements for air quality applications will be illustrated for Europe and China. Furthermore, we show comparisons of the TROPOMI NO2 data with ground-based MAX-DOAS and GOME-2 satellite measurements; the tropospheric ozone columns from TROPOMI are compared to ozone sonde data and OMPS satellite measurements.