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Andreas

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Authored

S5P/TROPOMI: The first year in orbit

Abstract (2018) - Joris Pepijn Veefkind, Ilse Aben, Angelika Dehn, Quintus Kleipool, Jochen Landgraf, Diego G. Loyola, Andreas Richter, Michel van Roozendael, Pieternel Felicitas Levelt

On 13 October 2017 the European Sentinel 5 Precursor was successfully launched, with on board the TROPOMI (TROPOspheric Monitoring Instrument). TROPOMI is an imaging spectrometer developed by The Netherlands and ESA for monitoring the atmospheric composition, for air quality climate and ozone layer monitoring. The launch of TROPOMI marks the start of operational atmospheric composition measurements from space within the European Copernicus programme, the largest Earth observation programme in the world. After one month of instrument checkout, the first light of TROPOMI was received in November 2017. During the commissioning phase the TROPOMI instrument settings were optimized. This included an increase in the spatial sampling from 7x7 to 3.5x7 km2(across track x along track), for most of the TROPOMI spectral bands. The S5P commissioning phase was completed half a year after launch and on 30 April 2018 the routine operations were started. The first batch of data products was publicly released on 11 July 2018. By the time of the AGU fall meeting, almost all the data products must have been released. TROPOMI has provided very exciting results during its first year in orbit. Very remarkable are the plumes of short-lived gases like NO2, which can extend several tens of kilometers from the source. These plumes were predicted by air quality models; however it requires the spatial resolution of TROPOMI to see them from space. Also, the CO maps have attracted a lot of attention. Because of the high sensitivity for the entire vertical column, both the sources as well as the transport of CO are clearly visible in the TROPOMI data. The high spatial resolution of the TROPOMI data also poses new challenges. More than for the previous satellite sensors, the need for accurate modelling of the surface reflectance becomes clear. Also, the 3D effects of clouds are now more prominent. All these aspects are also important for the upcoming geostationary missions within the CEOS air quality constellation. In this presentation an overview will be given of the status of the mission, including the in-orbit calibration and the data products. Specific results will be highlighted that illustrate the new capabilities of TROPOMI and also the challenges that need to be addressed in future updates of the data products.@en

Contributed

Aerosols correction of the OMI tropospheric NO2 retrievals over cloud-free scenes

Different methodologies based on the O2-O2 477 nm band

Abstract (2016) - J.J. Chimot, T. Vlemmix, j. Pepijn Veefkind, Pieternel Felicitas Levelt, Andreas Richter

Numerous studies have drawn attention to the complexities related to the retrievals of tropospheric NO2 columns derived from satellite UltraViolet-Visible (UV-Vis) measurements in the presence of aerosols. Correction for aerosol effects will remain a challenge for the next generation of air quality satellite instruments such as TROPOMI on Sentinel-5 Precursor, Sentinel-4 and Sentinel-5. The Ozone Monitoring Instrument (OMI) instrument has provided daily global measurements of tropospheric NO2 for more than a decade. However, aerosols are not explicitly taken into account in the current operational OMI tropospheric NO2 retrieval chain (DOMINO v2 [Boersma et al., 2011]). Our study analyses 2 approaches for an operational aerosol correction, based on the use of the O2-O2 477 nm band. The 1st approach is the cloud-model based aerosol correction, also named “implicit aerosol correction”, and already used in the operational chain. The OMI O2-O2 cloud retrieval algorithm, based on the Differential Optical Absorption Spectroscopy (DOAS) approach, is applied both to cloudy and to cloud-free scenes with aerosols present. Perturbation of the OMI cloud retrievals over scenes dominated by aerosols has been observed in recent studies led by [Castellanos et al., 2015; Lin et al., 2015; Lin et al., 2014]. We investigated the causes of these perturbations by: (1) confronting the OMI tropospheric NO2, clouds and MODIS AQUA aerosol products; (2) characterizing the key drivers of the aerosol net effects, compared to a signal from clouds, in the UV-Vis spectra. This study has focused on large industrialised areas like East-China, over cloud-free scenes. One of the key findings is the limitation due to the coarse sampling of the employed cloud Look-Up Table (LUT) to convert the results of the applied DOAS fit into effective cloud fraction and pressure. This leads to an underestimation of tropospheric NO2 amount in cases of particles located at elevated altitude. A higher sampling of the variation of O2-O2 SCD and continuum reflectance as a function of effective cloud parameters in case of low effective cloud fraction values is requested for applying an aerosol correction. The updates of the OMI O2-O2 cloud algorithm, based on the scheduled new OMI cloud LUT, will be presented in terms of impacts of the effective cloud retrievals and reduced biases of tropospheric NO2 columns over cloud-free scenes dominated by aerosols in China. A 2nd approach is investigated, assuming a more explicit aerosol correction. Previous analyses pointed out that the O2-O2 spectra contain information about aerosols: the continuum reflectance is primarily constrained by the Aerosol Optical thickness (AOT) while the O2-O2 Slant Column Density (SCD) mostly results from the combination of AOT and aerosols altitude. We have developed a first prototype algorithm allowing to retrieve information about AOT and aerosol altitude from the O2-O2 DOAS fit. We will discuss preliminary sensitivities and the potential accuracy of the associated explicit aerosol correction, without the use of effective cloud parameters. @en