Sentinel-5 Precursor (S-5P)

The S-5P mission is the first of the Sentinel series missions dedicated to the atmospheric composition monitoring. The instrument on board is the TROPOspheric Monitoring Instrument (TROPOMI) equipped with four spectrometers covering the UV-VIS-NIR-SWIR part of the solar spectrum. Within this spectrum, a number of trace gases (e.g., O3, SO2, HCHO, NO2, CO, CH4) and atmospheric components (i.e., aerosols and clouds) can be retrieved. The cloud retrieval algorithm called ROCINN (Retrieval of Cloud Information using Neural Network) makes use of the absorption of O2 A-band molecule in the near infrared band. The precise retrieval of the cloud properties prior to the computation of trace gas concentrations is fundamental for the accuracy of the latter. The high spatial resolution of TROPOMI is advantageous compared to previous missions (e.g., GOME2) because it will increase the frequency of cloud free pixels and this will allow the computation of tropospheric trace gases for larger areas.

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The gas retrievals especially the tropospheric products are affected by the presence of clouds. Even though O3 is mainly located in the stratosphere at altitudes of about 20-30 km, very frequently, we observe increased concentrations of O3 in the troposphere due to stratosphere-troposphere-exchange (STE) processes. The STE is more evident in the tropics where the tropopause occurs at very high altitudes (e.g., 18 km). The tropospheric O3 around the Equator is shown at the left panel of Figure 2. Ozone could also be a pollutant when it is produced close to the ground level through photochemical reactions. Another indicator of air quality and proxy for volatile organic compound emissions is the formaldehyde (HCHO). The global distribution of HCHO is depicted in the global map presented in the middle panel of the Figure. Sulphur dioxide (SO2) has an anthropogenic source but very frequently is released in the atmosphere due to volcanic activity (i.e., during a volcanic eruption or out-gassing process). An eruption of volcano Agung in Bali at 25 November 2017 has been identified by the increased SO2 concentration shown in the bottom panel of the Figure.


  • Loyola, D. G.; Gimeno García, S.; Lutz, R.; Argyrouli, A.; Romahn, F.; Spurr, R. J. D.; Pedergnana, M.; Doicu, A.; Molina García, V.; Schüssler, O.: The Operational Cloud Retrieval Algorithms from TROPOMI on board Sentinel-5 Precursor. Atmospheric Measurement Techniques 11 (1), 2018, 409--427 mehr…