Validation of Sentinel-5P TROPOMI tropospheric NO2 products by comparison with NO2 measurements from airborne imaging, ground-based stationary, and mobile car DOAS measurements during the S5P-VAL-DE-Ruhr campaign

Airborne imaging differential optical absorption spectroscopy (DOAS), ground-based stationary and car DOAS measurements were conducted during the S5P-VAL-DE-Ruhr campaign in September 2020. The campaign area is located in the Rhine-Ruhr region of North Rhine-Westphalia, Western Germany, which is a pollution hotspot in Europe comprising urban and large industrial emitters. The measurements are used to validate space-borne NO2 tropospheric vertical column density data products from the Sentinel-5 Precursor (S5P) TROPOspheric Monitoring Instrument (TROPOMI). Seven flights were performed with the airborne imaging DOAS instrument for measurements of atmospheric pollution (AirMAP), providing measurements which were used to create continuous maps of NO2 in the layer below the aircraft. These flights cover many S5P ground pixels within an area of 30 km x 35 km and were accompanied by ground-based stationary measurements and three mobile car DOAS instruments. Stationary measurements were conducted by two Pandora, two zenith-sky and two MAX-DOAS instruments distributed over three target areas. Ground-based stationary and car DOAS measurements are used to evaluate the AirMAP tropospheric NO2 vertical column densities and show high Pearson correlation coefficients of 0.87 and 0.89 and slopes of 0.93 &plusmn; 0.09 and 0.98 &plusmn; 0.02 for the stationary and car DOAS, respectively. Having a spatial resolution of about 100 m x 30 m, the AirMAP tropospheric NO2 vertical column density (VCD) data creates a link between the ground-based and the TROPOMI measurements with a resolution of 3.5 km x 5.5 km and is therefore well suited to validate the TROPOMI tropospheric NO2 VCD. The measurements on the seven flight days show strong NO2 variability, which is dependent on the different target areas, the weekday, and the meteorological conditions. The AirMAP campaign dataset is compared to the TROPOMI NO2 operational off-line (OFFL) V01.03.02 data product, the reprocessed NO2 data, using the V02.03.01 of the official L2 processor, provided by the Product Algorithm Laboratory (PAL), and several scientific TROPOMI NO2 data products. The TROPOMI data products and the AirMAP data are highly correlated with correlation coefficients between 0.72 and 0.87, and slopes of 0.38 &plusmn; 0.02 to 1.02 &plusmn; 0.07. On average, TROPOMI tropospheric NO2 VCDs are lower than the AirMAP NO2 results. The slope increased from 0.38 &plusmn; 0.02 for the operational OFFL V01.03.02 product to 0.83 &plusmn; 0.06 after the improvements in the retrieval of the PAL V02.03.01 product were implemented. Different auxiliary data, such as spatially higher resolved a priori NO2 vertical profiles, surface reflectivity and the cloud treatment, are investigated using scientific TROPOMI tropospheric NO2 VCD data products to evaluate their impact on the operational TROPOMI NO2 VCD data product. The comparison of the AirMAP campaign dataset to the scientific data products shows that the choice of surface reflectivity data base has a minor impact on the tropospheric NO2 VCD retrieval in the campaign region and season. In comparison, the replacement of the a priori NO2 profile in combination with the improvements in the retrieval of the PAL V02.03.01 product regarding cloud heights has a major impact on the tropospheric NO2 VCD retrieval and increases the slope from 0.88 &plusmn; 0.06 to 1.00 &plusmn; 0.07. This study demonstrates that the underestimation of the TROPOMI tropospheric NO2 VCD product with respect to the validation dataset has been and can be further significantly improved.</p

OMEGA - OSIRIS Mapping of Emission-line Galaxies in A901/2: I. Survey description, data analysis, and star formation and AGN activity in the highest density regions

We present an overview of and first results from the OMEGA (OSIRIS Mapping of Emission-line Galaxies in the multicluster system A901/2) survey. The ultimate goal of this project is to study star formation and active galactic nucleus (AGN) activity across a broad range of environments at a single redshift. Using the tuneable-filter mode of the Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) instrument on Gran Telescopio Canarias, we target Hα and [NII] emission lines over an ∼0.5×0.5 deg2 region containing the z∼0.167 multicluster system A901/2. In this paper, we describe the design of the survey, the observations and the data analysis techniques developed. We then present early results from two OSIRIS pointings centred on the cores of the A901a and A902 clusters. AGN and star-forming (SF) objects are identified using the [NII]/Hα versus WHα diagnostic diagram. The AGN hosts are brighter, more massive, and possess earlier type morphologies than SF galaxies. Both populations tend to be located towards the outskirts of the high-density regions we study. The typical Hα luminosity of these sources is significantly lower than that of field galaxies at similar redshifts, but greater than that found for A1689, a rich cluster at z∼0.2. The Hα luminosities of our objects translate into star formation rates (SFRs) between ∼0.02 and 6 Myr−1. Comparing the relationship between stellar mass and Hα-derived SFR with that found in the field indicates a suppression of star formation in the cores of the clusters. These findings agree with previous investigations of this multicluster structure, based on other star formation indicators, and demonstrate the power of tuneable filters for this kind of study

Pan-Atlantic connectivity of marine biogeochemical and ecological processes and the impact of anthropogenic pressures, SO287, 11.12.2021 - 11.01.2022, Las Palmas (Spain) - Guayaquil (Ecuador)

The transit of RV SONNE from Las Palmas (departure: 11.12.2021) to Guayaquil, Ecuador (arrival: 11.01.2022) is directly related to the international collaborative project SO287-CONNECT of GEOMAR in cooperation with Hereon and the University of Bremen, supported by the German Federal Ministry of Education and Research (BMBF) between October 15 2021 and January 15 2024. The research expedition was conducted to decipher the coupling of biogeochemical and ecological processes and their influence on atmospheric chemistry along the transport pathway of water from the upwelling zones off Africa into the Sargasso Sea and further to the Caribbean and the equatorial Pacific. Nutrient-rich water rises from the deep and promotes the growth of plant and animal microorganisms, and fish at the ocean surface off West Africa. The North Equatorial Current water carries the water from the upwelling, which contains large amounts of organic material across the Atlantic to the Caribbean, supporting bacterial activity along the way. But how the nutritious remnants of algae and other substances are processed on their long journey, biochemically transformed, decomposed into nutrients and respired to carbon dioxide, has so far only been partially investigated. Air, seawater and particles were sampled in order to provide new details about the large cycles of carbon and nitrogen, but also of many other elements such as oxygen, iodine, bromine and sulfur. Inorganic and organic bromine and iodine compounds are generally emitted naturally from the ocean into the atmosphere, promote cloud formation and affect climate, and some even reach the stratosphere where they contribute to ozone depletion. We measured how much of these compounds are released from the ocean, and at what locations and how they are transformed in the ocean and in the atmosphere. Sargassum algae, which have become a nuisance on beaches in the western and eastern Atlantic, support life and contribute to carbon cycling in the middle of the Atlantic, the Sargasso Sea and in the Caribbean, while their contribution to halogen cycling and marine bromine and iodine emissions was previously unknown. We investigated the influence of various natural parameters such as temperature and solar radiation on the biogeochemical transformation processes in order to understand the influence of climate change on these processes in incubation experiments with seawater and algae. We investigated how anthropogenic signals such as shipping traffic influence the nitrogen and sulphur cycle in the ocean, as well as the impact of nitrogen oxides from ship exhaust and sulphurous, acidic and dirty water from purification systems on organisms and biochemical processes. Plastic debris was sampled from the surface waters to investigate its contribution to global biogeochemical transformation processes. The working hypotheses of the research program were: Bioavailability of dissolved organic carbon in surface waters decreases along the productivity gradient and transport pathway from the Eastern to the Western Tropical North Atlantic. Nutrient gradients from East to West constrain the microbial utilization of organic matter- contributing to an accumulation of C-rich organic matter due to a) limited mineralization and b) enhanced exudation- also leading to gel-like particles accumulation in the western tropical North Atlantic and Sargasso Sea. Tropospheric and stratospheric ozone are strongly impacted by biogeochemical and ecological processes occurring around and in the NA gyre system related to marine iodine and bromine cycles. The long-range transport of natural and anthropogenic organic matter in water and of gases and aerosols in the air impact carbon-export, biogeochemical cycles in the water column, and the release of gases and particles from the ocean significantly. 4 SONNE -Berichte, SO287, Las Palmas - Guayaquil, 11.12.2021 - 11.01.202 The data and samples obtained specifically target carbon, nutrient and halogen cycling, the composition of phytoplankton, bacteria, the transport and sequestration of macro algae and the air-sea exchange processes of climate relevant gases and aerosols. The influence of ecological and transport processes, as well as anthropogenic impacts on the North Atlantic gyre system, specifically in the Sargasso Sea and the influence of ship emissions throughout the Atlantic towards the west and into the Pacific will be investigated with the data

Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV¿visible spectrometers during CINDI-2

40 pags., 22 figs., 13 tabs.In September 2016, 36 spectrometers from 24 institutes measured a number of key atmospheric pollutants for a period of 17¿d during the Second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2) that took place at Cabauw, the Netherlands (51.97¿¿N, 4.93¿¿E). We report on the outcome of the formal semi-blind intercomparison exercise, which was held under the umbrella of the Network for the Detection of Atmospheric Composition Change (NDACC) and the European Space Agency (ESA). The three major goals of CINDI-2 were (1) to characterise and better understand the differences between a large number of multi-axis differential optical absorption spectroscopy (MAX-DOAS) and zenith-sky DOAS instruments and analysis methods, (2) to define a robust methodology for performance assessment of all participating instruments, and (3) to contribute to a harmonisation of the measurement settings and retrieval methods. This, in turn, creates the capability to produce consistent high-quality ground-based data sets, which are an essential requirement to generate reliable long-term measurement time series suitable for trend analysis and satellite data validation. The data products investigated during the semi-blind intercomparison are slant columns of nitrogen dioxide (NO2), the oxygen collision complex (O4) and ozone (O3) measured in the UV and visible wavelength region, formaldehyde (HCHO) in the UV spectral region, and NO2 in an additional (smaller) wavelength range in the visible region. The campaign design and implementation processes are discussed in detail including the measurement protocol, calibration procedures and slant column retrieval settings. Strong emphasis was put on the careful alignment and synchronisation of the measurement systems, resulting in a unique set of measurements made under highly comparable air mass conditions. The CINDI-2 data sets were investigated using a regression analysis of the slant columns measured by each instrument and for each of the target data products. The slope and intercept of the regression analysis respectively quantify the mean systematic bias and offset of the individual data sets against the selected reference (which is obtained from the median of either all data sets or a subset), and the rms error provides an estimate of the measurement noise or dispersion. These three criteria are examined and for each of the parameters and each of the data products, performance thresholds are set and applied to all the measurements. The approach presented here has been developed based on heritage from previous intercomparison exercises. It introduces a quantitative assessment of the consistency between all the participating instruments for the MAX-DOAS and zenith-sky DOAS techniques.CINDI-2 received funding from the Netherlands Space Office (NSO). Funding for this study was provided by ESA through the CINDI-2 (ESA contract no. 4000118533/16/ISbo) and FRM4DOAS (ESA contract no. 4000118181/16/I-EF) projects and partly within the EU 7th Framework Programme QA4ECV project (grant agreement no. 607405). The BOKU MAX-DOAS instrument was funded and the participation of Stefan F. Schreier was supported by the Austrian Science Fund (FWF): I 2296-N29. The participation of the University of Toronto team was supported by the Canadian Space Agency (through the AVATARS project) and the Natural Sciences and Engineering Research Council (through the PAHA project). The instrument was primarily funded by the Canada Foundation for Innovation and is usually operated at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network for the Detection of Atmospheric Change (CANDAC). Funding for CISC was provided by the UVAS (“Ultraviolet and Visible Atmospheric Sounder”) projects SEOSAT/INGENIO, ESP2015-71299- R, MINECO-FEDER and UE. The activities of the IUP-Heidelberg were supported by the DFG project RAPSODI (grant no. PL 193/17-1). SAOZ and Mini-SAOZ instruments are supported by the Centre National de la Recherche Scientifique (CNRS) and the Centre National d’Etudes Spatiales (CNES). INTA recognises support from the National funding projects HELADO (CTM2013-41311-P) and AVATAR (CGL2014-55230-R). AMOIAP recognises support from the Russian Science Foundation (grant no. 16-17-10275) and the Russian Foundation for Basic Research (grant nos. 16-05- 01062 and 18-35-00682). Ka L. Chan received transnational access funding from ACTRIS-2 (H2020 grant agreement no. 654109). Rainer Volkamer recognises funding from NASA’s Atmospheric Composition Program (NASA-16-NUP2016-0001) and the US National Science Foundation (award AGS-1620530). Henning Finkenzeller is the recipient of a NASA graduate fellowship. Mihalis Vrekoussis recognises support from the University of Bremen and the DFG Research Center/Cluster of Excellence “The Ocean in the Earth System-MARUM”. Financial support through the University of Bremen Institutional Strategy in the framework of the DFG Excellence Initiative is gratefully appreciated for Anja Schönhardt. Pandora instrument deployment was supported by Luftblick through the ESA Pandonia Project and NASA Pandora Project at the Goddard Space Flight Center under NASA Headquarters’ Tropospheric Composition Program. The article processing charges for this open-access publication were covered by BK Scientific

Detailierte Analyse von MAX-DOAS Messungen in Bremen : räumliche und zeitliche Verteilung von Aerosolen, Formaldehyd und Stickstoffdioxid

In this thesis, spatial and temporal tropospheric inhomogeneities in the distribution of nitrogen dioxide (NO2), formaldehyde (HCHO) and aerosols are investigated. The analysis was done on a three years dataset (2015 - 2017) of ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Bremen. MAX-DOAS measurements were investigated in three different azimuthal viewing directions in order to analyse lateral changes in the distribution of NO2 and HCHO in Bremen. A clear seasonality was found and explained by anthropogenic and biogenic emissions for NO2 and HCHO, respectively. While no significant azimuthal variability for HCHO was found, NO2 differs strongly for the westerly and southerly directions due to lateral inhomogeneities and a more frequent pointing towards the sun which has a strong impact on the results. In order to localize possible dominant emission sources of NO2 within the area of Bremen, the onion peeling approach was successfully applied by usage of the three fitting windows in the ultra-violet (UV) and visible (vis) spectral range. Strong emitters could be identified having a large impact on average NO2 results. A major challenge for the analysis of trace gases in the troposphere is the usually insufficient knowledge of aerosols, which might have a large impact on spectroscopic measurements. The novel MAX-DOAS profiling algorithm BOREAS was developed and its accuracy is validated with the help of synthetic data as well as ancillary measurements of the CINDI-2 field campaign (Cabauw, the Netherlands, 2016). In contrast to other algorithms, BOREASa aerosol information are retrieved by minimizing the difference of O4 optical depths of measurements and forward modelling calculations. The resulting aerosol extinction coefficient profiles were used for the retrieval of vertical trace gas concentration profiles. In this thesis, several retrieval modes and various ways of improving the regularization between measurement and a priori constraints as well as the selection of proper a priori profiles by use of a priori pre-scaling were investigated. The BOREAS algorithm was finally applied to the full MAX-DOAS dataset, and three years of aerosol and trace gas vertical profiles from the measurement location Bremen are presented and discussed with the help of in-situ as well as AERONET measurements. Seasonal, weekday and diurnal cycles for aerosols and NO2 were found which could be attributed to near surface emissions mainly from traffic and power plants. The seasonal cycle of HCHO is found to be dominated by biogenic emissions in summer, in addition to a smaller fraction of anthropogenic emissions in winter. While NO2 and aerosols are mainly focussed in layers close to the surface, larger HCHO concentrations could also be observed in the complete planetary boundary layer showing the need for the analysis of vertical concentration profiles of trace gases in the troposphere

Detailed analysis of MAX-DOAS measurements in Bremen : spatial and temporal distribution of aerosols, formaldehyde and nitrogen dioxide

In this thesis, spatial and temporal tropospheric inhomogeneities in the distribution of nitrogen dioxide (NO2), formaldehyde (HCHO) and aerosols are investigated. The analysis was done on a three years dataset (2015 - 2017) of ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Bremen. MAX-DOAS measurements were investigated in three different azimuthal viewing directions in order to analyse lateral changes in the distribution of NO2 and HCHO in Bremen. A clear seasonality was found and explained by anthropogenic and biogenic emissions for NO2 and HCHO, respectively. While no significant azimuthal variability for HCHO was found, NO2 differs strongly for the westerly and southerly directions due to lateral inhomogeneities and a more frequent pointing towards the sun which has a strong impact on the results. In order to localize possible dominant emission sources of NO2 within the area of Bremen, the onion peeling approach was successfully applied by usage of the three fitting windows in the ultra-violet (UV) and visible (vis) spectral range. Strong emitters could be identified having a large impact on average NO2 results. A major challenge for the analysis of trace gases in the troposphere is the usually insufficient knowledge of aerosols, which might have a large impact on spectroscopic measurements. The novel MAX-DOAS profiling algorithm BOREAS was developed and its accuracy is validated with the help of synthetic data as well as ancillary measurements of the CINDI-2 field campaign (Cabauw, the Netherlands, 2016). In contrast to other algorithms, BOREASa aerosol information are retrieved by minimizing the difference of O4 optical depths of measurements and forward modelling calculations. The resulting aerosol extinction coefficient profiles were used for the retrieval of vertical trace gas concentration profiles. In this thesis, several retrieval modes and various ways of improving the regularization between measurement and a priori constraints as well as the selection of proper a priori profiles by use of a priori pre-scaling were investigated. The BOREAS algorithm was finally applied to the full MAX-DOAS dataset, and three years of aerosol and trace gas vertical profiles from the measurement location Bremen are presented and discussed with the help of in-situ as well as AERONET measurements. Seasonal, weekday and diurnal cycles for aerosols and NO2 were found which could be attributed to near surface emissions mainly from traffic and power plants. The seasonal cycle of HCHO is found to be dominated by biogenic emissions in summer, in addition to a smaller fraction of anthropogenic emissions in winter. While NO2 and aerosols are mainly focussed in layers close to the surface, larger HCHO concentrations could also be observed in the complete planetary boundary layer showing the need for the analysis of vertical concentration profiles of trace gases in the troposphere

FDR4ATMOS (Task B): FDR Long time series for spectral imagers

The Fundamental Data Record for ATMOSpheric Composition (FDR4ATMOS) project is part of the ESA Long Term Data Preservation (LTDP) programme. A Fundamental Data Record (FDR) is a long-term record of selected Earth observation Level 1 parameters (radiance, irradiance, reflectance), possibly multi-instrument, which provides improvements of performance with respect to the individual mission data sets. The aim of task B of the project is to be a pathfinder for future harmonisation of spectrally highly resolved data from other instruments, starting with 2 well known instruments GOME-1 and SCIAMACHY and the spectral ranges for the retrieval of SO2, O3 (UV), NO2 (VIS) and cloud properties (NIR). The FDR will contain harmonised irradiances and reflectances with associated uncertainties. The GOME-1 and SCIAMACHY instruments together span 17 years of spectrally highly resolved data essential for air quality, climate, ozone trend and UV radiation applications. We plan to generate harmonised data sets that allows to directly use it in long-term trend analysis, independently of the instrument. Since this was never done for highly resolved spectrometers, new methods have to be developed that e.g. take into account the different observation geometries for the Earth measurements: GOME-1 and SCIAMACHY had different orbits with a local descending node crossing time of 10:30 and 10:00 respectively resulting in different solar zenith angles. The spatial resolution also differs with GOME-1 having a resolution 40 × 320 km^2 and SCIAMACHY a resolution of 32 × 233 km^2 to 26 × 30 km^2, depending on the spectral range and orbit phase. Since the retrieval of atmospheric trace gas content and other parameters depends on the relative structures of the spectrum, any harmonisation must keep these structures and at the same time take care of broader band differences between the instruments. The data will also contain uncertainties that are based on metrological principles. For that purpose, we reviewed the error sources and error correlations of the original Level 1 data. These uncertainties will flow into the error propagation, leading to final uncertainties of the FDR. The resulting algorithms will be implemented into a processing system using the DLR developed GCAPS framework (Generic Calibration and Processing System). The purpose is to keep the methods and the implementation as generic as possible to be able to easily transfer the methodology to other wavelength ranges and to other instruments (e.g. GOME-2 and Sentinel-5p) for a future extension of the time series. Starting with the solar irradiance as the simpler problem (compared to the Earth radiance measurements) we investigated different methods for the harmonisation and will present the results in the paper. We will also describe the overall validation concept and the status of the harmonisation of the reflectances

The Status of the FDR4ATMOS Project

The Fundamental Data Record for ATMOSpheric Composition (FDR4ATMOS) project is part of the ESA Long Term Data Preservation (LTDP) programme and has two objectives: First, update the SCIAMACHY processing chain for better Ozone total column data: After the full re-processing of the SCIAMACHY mission with the updated processor versions, the validation showed that the total Ozone column drifted downward by nearly 2% over the mission lifetime. This drift is likely caused by changes in the degradation correction in the Level 1 processor, that led to subtle changes in the spectral structures. These are misinterpreted as an atmospheric signature. FDR4ATMOS updated the Level 0-1 processor accordingly and a full mission re-processing hast started. In an addition to the original plan, we also incorporated lunar data in the SCIAMACHYLevel 1b product. The instrument performed regular lunar observations buiding up a unique 10 year data set of lunar spectra from the UV to the SWIR with moderately high spectral resolution. In the project we calibrated these data. The results show an agreement within the error with other lunar data (e.g. ROLO). The second objective of the FDR4ATMOS project is to develop a cross-instrument Level 1 product for GOME-1 and SCIAMACHY for the UV, VIS and NIR spectral range, with focus on the spectral windows used for O3, SO2, NO2 total column retrieval and the determination of cloud properties. FDR4ATMOS aims to build a Fundamental Data Record (FDR) of Level 1 products, i.e. radiances and reflectances. The GOME-1 and SCIAMACHY instruments together span 17 years of spectrally highly resolved data essential for air quality, climate, ozone trend and UV radiation applications. We plan to generate harmonised data sets that allows to directly use it in long-term trend analysis, independently of the instrument. Since this was never done for highly resolved spectrometers, new methods have to be developed that e.g. take into account the different observation geometries and observation times of the instrument without impacting the spectral structures that are used for the retrieval of the atmospheric species. The resulting algorithms and the processor should also be as generic as possible to be able to easily transfer the methodology to other instruments (e.g. GOME-2 and Sentinel-5p) for a future extension of the time series. We will present the current status of the project, including results for the updated SCIAMACHY processor, the uncertainty analyses and will report the status of the data analysis for the harmonisation of data