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4. An improved TROPOMI tropospheric NO<sub>2</sub> research product over Europe

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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5. An improved tropospheric NO2 column retrieval algorithm for TROPOMI over Europe

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, Myrto, Hendrick, François, Karagkiozidis, Dimitris, Lange, Kezia, Piters, Ankie J. M., Remmers, Julia, Richter, Andreas, Roozendael, Michel, Wagner, Thomas, Wenig, Mark, and Loyola, Diego G.

Abstract

Launched in October 2017, the TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel-5 Precursor provides the potential to monitor air quality over point sources across the globe with a spatial resolution as high as 5.5 km × 3.5 km (7 km × 3.5 km before 6 August 2019). The nitrogen dioxide (NO2) retrieval algorithm for the TROPOMI instrument consists of three steps: the spectral fitting of the slant column, the separation of stratospheric and tropospheric contributions, and the conversion of the slant column to a vertical column using an air mass factor (AMF) calculation. In this work, an improved tropospheric NO2 retrieval algorithm from TROPOMI measurements over Europe is presented. The stratospheric estimation is implemented using the STRatospheric Estimation Algorithm from Mainz (STREAM), which was developed as a verification algorithm for TROPOMI and does not require chemistry transport model data as input. A directionally dependent STREAM (DSTREAM) is developed to correct for the dependency of the stratospheric NO2 on the viewing geometry by up to 2 × 1014 molec/cm2. Applied to synthetic TROPOMI data, the uncertainty in the stratospheric column is 3.5 × 1014 molec/cm2 for polluted conditions. Applied to actual measurements, the smooth variation of stratospheric NO2 at low latitudes is conserved, and stronger stratospheric variation at higher latitudes are captured. For AMF calculation, the climatological surface albedo data is replaced by geometry-dependent effective Lambertian equivalent reflectivity (GE_LER) obtained directly from TROPOMI measurements with a high spatial resolution. Mesoscale-resolution a priori NO2 profiles are obtained from the regional POLYPHEMUS/DLR chemistry transport model with the TNO-MACC emission inventory. Based on the latest TROPOMI operational cloud parameters, a more realistic cloud treatment is provided by a clouds-as-layers (CAL) model, which treats the clouds as uniform layers of water droplets, instead of the clouds-as-reflecting-boundaries (CRB) model, in which clouds are simplified as Lambertian reflectors. For the error analysis, the tropospheric AMF uncertainty, which is the largest source of NO2 uncertainty for polluted scenarios, ranges between 20 % and 50 %, leading to a total uncertainty in the tropospheric NO2 column in the 30–60 % range. From a validation performed with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, the improved tropospheric NO2 data shows good correlations for nine European urban/suburban stations with an average correlation coefficient of 0.78. The implementation of the algorithm improvements leads to a decrease of the relative difference from −55.3 % to −34.7 % on average.

Published
2021

6. Ground-based validation of the Copernicus Sentinel-5P TROPOMI NO2 measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

Author

Verhoelst, Tijl, Compernolle, Steven, Pinardi, Gaia, Lambert, Jean Christopher, Eskes, Henk J., Eichmann, Kai Uwe, Fjæraa, Ann Mari, Granville, José, Niemeijer, Sander, Cede, Alexander, Tiefengraber, Martin, Hendrick, François, Pazmiño, Andrea, Bais, Alkiviadis, Bazureau, Ariane, Boersma, K.F., Bognar, Kristof, Dehn, Angelika, Donner, Sebastian, Elokhov, Aleksandr, Gebetsberger, Manuel, Goutail, Florence, Grutter De La Mora, Michel, Gruzdev, Aleksandr, Gratsea, Myrto, Hansen, Georg H., Irie, Hitoshi, Jepsen, Nis, Kanaya, Yugo, Karagkiozidis, Dimitris, Kivi, Rigel, Kreher, Karin, Levelt, Pieternel F., Liu, Cheng, Müller, Moritz, Navarro Comas, Monica, Piters, Ankie J.M., Pommereau, Jean Pierre, Portafaix, Thierry, Prados-Roman, Cristina, Puentedura, Olga, Querel, Richard, Remmers, Julia, Richter, Andreas, Rimmer, John, Cárdenas, Claudia Rivera, De Miguel, Lidia Saavedra, Sinyakov, Valery P., Stremme, Wolfgang, Strong, Kimberly, Van Roozendael, Michel, Veefkind, J.P., Wagner, Thomas, Wittrock, Folkard, Yela González, Margarita, Zehner, Claus, Verhoelst, T. [0000-0003-0163-9984], Compernolle, S. [0000-0003-0872-0961], Pinardi, G. [0000-0001-5428-916X], Eskes, H. [0000-0002-8743-4455], Bais, A. [0000-0003-3899-2001], Folkert Boersma, K. [0000-0002-4591-7635], Bognar, K. [0000-0003-4619-2020], Donner, S. [0000-0001-8868-167X], Elokhov, A. [0000-0003-4725-9186], Grutter de la Mora, M. [0000-0001-9800-5878], Gruzdev, A. [0000-0003-3224-1012], Karagkiozidis, D. [0000-0002-3595-0538], Kivi, R. [0000-0001-8828-2759], Liu, C. [0000-0002-3759-9219], Müller, M. [0000-0001-5284-5425], Pommereau, J. P. [0000-0002-8285-9526], Prados Roman, C. [0000-0001-8332-0226], Puentedura, O. [0000-0002-4286-1867], Querel, R. [0000-0001-8792-2486], Richter, A. [0000-0003-3339-212X], Rivera Cárdenas, C. [0000-0002-8617-265X], Stremme, W. [0000-0003-0791-3833], Strong, K. [0000-0001-9947-1053], Pepijn Veefkind, J. [0000-0003-0336-6406], European Space Agency (ESA), French Institut National des Sciences de l'Univers (INSU), Centre National D'Etudes Spatiales (CNES), Centre National de la Recherche Scientifique (CNRS), Institut polaire français Paul Emile Victor (IPEV), and Belgian Science Policy Office (BELSPO)

Subjects
Meteorologie en Luchtkwaliteit, WIMEK, Meteorology and Air Quality, Copernicus Sentinel 5P, Life Science, Pandonia global networks
Abstract

This paper reports on consolidated ground-based validation results of the atmospheric NO2 data produced operationally since April 2018 by the TROPOspheric Monitoring Instrument (TROPOMI) on board of the ESA/EU Copernicus Sentinel-5 Precursor (S5P) satellite. Tropospheric, stratospheric, and total NO2 column data from S5P are compared to correlative measurements collected from, respectively, 19 Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), 26 Network for the Detection of Atmospheric Composition Change (NDACC) Zenith-Scattered-Light DOAS (ZSL-DOAS), and 25 Pandonia Global Network (PGN)/Pandora instruments distributed globally. The validation methodology gives special care to minimizing mismatch errors due to imperfect spatio-temporal co-location of the satellite and correlative data, e.g. by using tailored observation operators to account for differences in smoothing and in sampling of atmospheric structures and variability and photochemical modelling to reduce diurnal cycle effects. Compared to the ground-based measurements, S5P data show, on average, (i) a negative bias for the tropospheric column data, of typically −23 % to −37 % in clean to slightly polluted conditions but reaching values as high as −51 % over highly polluted areas; (ii) a slight negative median difference for the stratospheric column data, of about −0.2 Pmolec cm−2, i.e. approx. −2 % in summer to −15 % in winter; and (iii) a bias ranging from zero to −50 % for the total column data, found to depend on the amplitude of the total NO2 column, with small to slightly positive bias values for columns below 6 Pmolec cm−2 and negative values above. The dispersion between S5P and correlative measurements contains mostly random components, which remain within mission requirements for the stratospheric column data (0.5 Pmolec cm−2) but exceed those for the tropospheric column data (0.7 Pmolec cm−2). While a part of the biases and dispersion may be due to representativeness differences such as different area averaging and measurement times, it is known that errors in the S5P tropospheric columns exist due to shortcomings in the (horizontally coarse) a priori profile representation in the TM5-MP chemical transport model used in the S5P retrieval and, to a lesser extent, to the treatment of cloud effects and aerosols. Although considerable differences (up to 2 Pmolec cm−2 and more) are observed at single ground-pixel level, the near-real-time (NRTI) and offline (OFFL) versions of the S5P NO2 operational data processor provide similar NO2 column values and validation results when globally averaged, with the NRTI values being on average 0.79 % larger than the OFFL values. This research has been supported by the ESA/ESRIN (grant no. 4000117151/16/I-LG) and the BELSPO/ESA ProDEx (TROVA-E2 (PEA grant no. 4000116692)). Part of the reported work was carried out in the framework of the Copernicus Sentinel-5 Precursor Mission Performance Centre (S5P MPC), contracted by the European Space Agency and supported by the Belgian Federal Science Policy Office (BELSPO), the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), the Netherlands Space Office (NSO), and the German Aerospace Centre (DLR). Part of this work was carried out also in the framework of the S5P Validation Team (S5PVT) AO projects NIDFORVAL (ID no. 28607, PI Gaia Pinardi, BIRA-IASB) and CESAR (ID no. 28596, PI Arnoud Apituley, KNMI). The authors express special thanks to Ann Mari Fjæraa, José Granville, Sander Niemeijer, and Olivier Rasson for post-processing of the network and satellite data and for their dedication to the S5P operational validation. The LATMOS real-time processing facility is acknowledged for fast delivery of ZSL-DOAS SAOZ data. Fast delivery of MAX-DOAS data tailored to the S5P validation was organized through the S5PVT AO project NIDFORVAL. The authors are grateful to ESA/ESRIN for supporting the ESA Validation Data Centre (EVDC) established at NILU and for running the Fiducial Reference Measurements (FRM) programme and in particular the FRM4DOAS and Pandonia projects. The PGN is a bilateral project between NASA and ESA, and the NASA funding for the PGN is provided through the NASA Tropospheric Composition Program and Goddard Space Flight Center Pandora project. The MAX-DOAS, ZSL-DOAS, and PGN instrument PIs and staff at the stations are thanked warmly for their sustained effort on maintaining high-quality measurements and for valuable scientific discussions. Aleksandr Elokhov and Aleksandr Gruzdev acknowledge national funding from RFBR through the project 20-95-00274. IUP Bremen acknowledges DLR Bonn for funding received through project 50EE1709A. The SAOZ network acknowledges funding from the French Institut National des Sciences de l'Univers (INSU) of the Centre National de la Recherche Scientifique (CNRS), Centre National d'Etudes Spatiales (CNES), and Institut polaire français Paul Emile Victor (IPEV). Work done by Hitoshi Irie was supported by the Environment Research and Technology Development Fund (2-1901) of the Environmental Restoration and Conservation Agency of Japan, JSPS KAKENHI (grant nos. JP19H04235 and JP17K00529), the JAXA 2nd Research Announcement on the Earth Observations (grant no. 19RT000351), and JST CREST (grant no. JPMJCR15K4). The University of Toronto ZSL-DOAS measurements at Eureka were made at the Polar Environment Atmospheric Research Laboratory (PEARL) by the Canadian Network for the Detection of Atmospheric Change (CANDAC), with support from the Canadian Space Agency (AVATARS project), the Natural Sciences and Engineering Research Council (PAHA project), and Environment and Climate Change Canada. Peerreview

Published
2021

8. Evaluation of the LOTOS-EUROS NO<sub>2</sub> simulations using ground-based measurements and S5P/TROPOMI observations over Greece

Author

Skoulidou, Ioanna, primary, Koukouli, Maria-Elissavet, additional, Manders, Astrid, additional, Segers, Arjo, additional, Karagkiozidis, Dimitris, additional, Gratsea, Myrto, additional, Balis, Dimitris, additional, Bais, Alkiviadis, additional, Gerasopoulos, Evangelos, additional, Stavrakou, Trisevgeni, additional, van Geffen, Jos, additional, Eskes, Henk, additional, and Richter, Andreas, additional

Published
2021
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9. An improved TROPOMI tropospheric NO2 research product over Europe

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, Myrto, Hendrick, François, Karagkiozidis, Dimitris, Lange, Kezia, Piters, Ankie J. M., Remmers, Julia, Richter, Andreas, Van Roozendael, Michel, Wagner, Thomas, Wenig, Mark, and Loyola, Diego G.

Subjects
ddc
Published
2020

10. Supplementary material to "An improved tropospheric NO<sub>2</sub> column retrieval algorithm for TROPOMI over Europe"

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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11. An improved tropospheric NO2 column retrieval algorithm for TROPOMI over Europe

Author

Liu, Song, primary, Valks, Pieter, additional, Pinardi, Gaia, additional, Xu, Jian, additional, Chan, Ka Lok, additional, Argyrouli, Athina, additional, Lutz, Ronny, additional, Beirle, Steffen, additional, Khorsandi, Ehsan, additional, Baier, Frank, additional, Huijnen, Vincent, additional, Bais, Alkiviadis, additional, Donner, Sebastian, additional, Dörner, Steffen, additional, Gratsea, Myrto, additional, Hendrick, François, additional, Karagkiozidis, Dimitris, additional, Lange, Kezia, additional, Piters, Ankie J. M., additional, Remmers, Julia, additional, Richter, Andreas, additional, Van Roozendael, Michel, additional, Wagner, Thomas, additional, Wenig, Mark, additional, and Loyola, Diego G., additional

Published
2021
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12. Retrieval and evaluation of tropospheric-aerosol extinction profiles using multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements over Athens, Greece

Author

Gratsea, Myrto, primary, Bösch, Tim, additional, Kokkalis, Panagiotis, additional, Richter, Andreas, additional, Vrekoussis, Mihalis, additional, Kazadzis, Stelios, additional, Tsekeri, Alexandra, additional, Papayannis, Alexandros, additional, Mylonaki, Maria, additional, Amiridis, Vassilis, additional, Mihalopoulos, Nikos, additional, and Gerasopoulos, Evangelos, additional

Published
2021
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13. Ground-based validation of the Copernicus Sentinel-5p TROPOMI NO2 measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

Author

Verhoelst, Tiji, Compernolle, Steven, Pinardi, Gala, Lambert, Jean-Christopher, Eskes, Henk J., Eichmann, Kai-Uwe, Fjæraa, Ann Mari, Granville, José, Niemeijer, Sander, Cede, Alexander, Tiefengraber, Martin, Hendrick, François, Pazmino, Andrea, Bais, Alkiviadis, Bazureau, Ariane, Boersma, Klaas Folkert, Bognar, Kristof, Dehn, Angelika, Donner, Sebastian, Elokhov, Aleksandr, Gebetsberger, Manuel, Goutail, Florence, Grutter de la Mora, Michel, Gruzdev, Aleksandr, Gratsea, Myrto, Hansen, Georg, Irie, Hitoshi, Jepsen, Nis, Kanaya, Yugo, Karagkiozidis, Dimitris, Kivi, Rigel, Kreher, Karin, Levelt, Pieternel F., Liu, Cheng, Müller, Moritz, Navarro-Comas, Monica, Piters, Ankie J. M., Pommereau, Jean-Pierre, Portafaix, Thierry, Puentedura, Olga, Querel, Richard, Remmers, Julia, Richter, Andreas, Rimmer, John, Rivera Cárdenas, Claudia, Saavedra De Miguel, Lidia, Sinyakov, Valery P., Strong, Kimberley, Van Roozendaël, Michel, Veefkind, Pepijn J., Wagner, Thomas, Wittrock, Folkard, Yela-González, Margarita, Zehner, Claus, Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique (BIRA-IASB), Royal Netherlands Meteorological Institute (KNMI), Institut für Umweltphysik [Bremen] (IUP), Universität Bremen, Norsk Institutt for Luftforskning (NILU), Science [&] Technology Corporation [Delft] (S [&] T), NASA Goddard Space Flight Center (GSFC), Institute of Meteorology and Geophysics [Innsbruck], University of Innsbruck, STRATO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Laboratory of Atmospheric Physics [Thessaloniki], Aristotle University of Thessaloniki, Meteorology and Air Quality Group, Wageningen University and Research [Wageningen] (WUR), Department of Physics [Toronto], University of Toronto, European Space Research Institute (ESRIN), European Space Agency (ESA), Max-Planck-Institut für Chemie (MPIC), Max-Planck-Gesellschaft, A.M.Obukhov Institute of Atmospheric Physics (IAP), Russian Academy of Sciences [Moscow] (RAS), Centro de Ciencias de la Atmosfera [Mexico], Universidad Nacional Autónoma de México (UNAM), National Observatory of Athens (NOA), Center for Environmental Remote Sensing [Chiba] (CEReS), Chiba University, Danish Meteorological Institute (DMI), Research Institute for Global Change (RIGC), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Space and Earth Observation Centre [Sodankylä], Finnish Meteorological Institute (FMI), BK Scientific GmbH, Delft University of Technology (TU Delft), Department of Precision Machinery and Precision Instrumentation [Hefei], University of Science and Technology of China [Hefei] (USTC), Instituto Nacional de Técnica Aeroespacial (INTA), Laboratoire de l'Atmosphère et des Cyclones (LACy), Météo France-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), National Institute of Water and Atmospheric Research [Lauder] (NIWA), University of Manchester [Manchester], Kyrgyz National University, Institute of Environmental Physics [Bremen] (IUP), and University of Bremen

Subjects
[SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere
Abstract

This paper reports on consolidated ground-based validation results of the atmospheric NO2 data produced operationally since April 2018 by the TROPOMI instrument on board of the ESA/EU Copernicus Sentinel-5 Precursor (S5p) satellite. Tropospheric, stratospheric, and total NO2 column data from S5p are compared to correlative measurements collected from, respectively, 19 Multi-Axis DOAS (MAX-DOAS), 26 NDACC Zenith-Scattered-Light DOAS (ZSL-DOAS), and 25 PGN/Pandora instruments distributed globally. The validation methodology gives special care to minimizing mismatch errors due to imperfect spatio-temporal co-location of the satellite and correlative data, e.g., by using tailored observation operators to account for differences in smoothing and in sampling of atmospheric structures and variability, and photochemical modelling to reduce diurnal cycle effects. Compared to the ground-based measurements, S5p data show, on an average: (i) a negative bias for the tropospheric column data, of typically −23 to −37 % in clean to slightly polluted conditions, but reaching values as high as −51 % over highly polluted areas; (ii) a slight negative bias for the stratospheric column data, of about −0.2 Pmolec/cm2, i.e. approx. −2 % in summer to −15 % in winter; and (iii) a bias ranging from zero to −50 % for the total column data, found to depend on the amplitude of the total NO2 column, with small to slightly positive bias values for columns below 6 Pmolec/cm2 and negative values above. The dispersion between S5p and correlative measurements contains mostly random components, which remain within mission requirements for the stratospheric column data (0.5 Pmolec/cm2), but exceed those for the tropospheric column data (0.7 Pmolec/cm2). While a part of the biases and dispersion may be due to representativeness differences, it is known that errors in the S5p tropospheric columns exist due to shortcomings in the (horizontally coarse) a-priori profile representation in the TM5-MP chemistry transport model used in the S5p retrieval, and to a lesser extent, to the treatment of cloud effects. Although considerable differences (up to 2 Pmolec/cm2 and more) are observed at single ground-pixel level, the near-real-time (NRTI) and off-line (OFFL) versions of the S5p NO2 operational data processor provide similar NO2 column values and validation results when globally averaged, with the NRTI values being on average 0.79 % larger than the OFFL values.

Published
2020

14. Supplementary material to "Evaluation of the LOTOS-EUROS NO2 simulations using ground-based measurements and S5P/TROPOMI observations over Greece"

Author

Skoulidou, Ioanna, primary, Koukouli, Maria-Elissavet, additional, Manders, Astrid, additional, Segers, Arjo, additional, Karagkiozidis, Dimitris, additional, Gratsea, Myrto, additional, Balis, Dimitris, additional, Bais, Alkiviadis, additional, Gerasopoulos, Evangelos, additional, Stavrakou, Trisevgeni, additional, van Geffen, Jos, additional, Eskes, Henk, additional, and Richter, Andreas, additional

Published
2020
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15. Evaluation of the LOTOS-EUROS NO2 simulations using ground-based measurements and S5P/TROPOMI observations over Greece

Author

Skoulidou, Ioanna, primary, Koukouli, Maria-Elissavet, additional, Manders, Astrid, additional, Segers, Arjo, additional, Karagkiozidis, Dimitris, additional, Gratsea, Myrto, additional, Balis, Dimitris, additional, Bais, Alkiviadis, additional, Gerasopoulos, Evangelos, additional, Stavrakou, Trisevgeni, additional, van Geffen, Jos, additional, Eskes, Henk, additional, and Richter, Andreas, additional

Published
2020
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17. Ground-based validation of the Copernicus Sentinel-5p TROPOMI NO2 measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

Author

Verhoelst, Tijl, primary, Compernolle, Steven, additional, Pinardi, Gaia, additional, Lambert, Jean-Christopher, additional, Eskes, Henk J., additional, Eichmann, Kai-Uwe, additional, Fjæraa, Ann Mari, additional, Granville, José, additional, Niemeijer, Sander, additional, Cede, Alexander, additional, Tiefengraber, Martin, additional, Hendrick, François, additional, Pazmiño, Andrea, additional, Bais, Alkiviadis, additional, Bazureau, Ariane, additional, Boersma, K. Folkert, additional, Bognar, Kristof, additional, Dehn, Angelika, additional, Donner, Sebastian, additional, Elokhov, Aleksandr, additional, Gebetsberger, Manuel, additional, Goutail, Florence, additional, Grutter de la Mora, Michel, additional, Gruzdev, Aleksandr, additional, Gratsea, Myrto, additional, Hansen, Georg H., additional, Irie, Hitoshi, additional, Jepsen, Nis, additional, Kanaya, Yugo, additional, Karagkiozidis, Dimitris, additional, Kivi, Rigel, additional, Kreher, Karin, additional, Levelt, Pieternel F., additional, Liu, Cheng, additional, Müller, Moritz, additional, Navarro Comas, Monica, additional, Piters, Ankie J. M., additional, Pommereau, Jean-Pierre, additional, Portafaix, Thierry, additional, Puentedura, Olga, additional, Querel, Richard, additional, Remmers, Julia, additional, Richter, Andreas, additional, Rimmer, John, additional, Rivera Cárdenas, Claudia, additional, Saavedra de Miguel, Lidia, additional, Sinyakov, Valery P., additional, Strong, Kimberley, additional, Van Roozendael, Michel, additional, Veefkind, J. Pepijn, additional, Wagner, Thomas, additional, Wittrock, Folkard, additional, Yela González, Margarita, additional, and Zehner, Claus, additional

Published
2020
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18. Retrieval and evaluation of tropospheric aerosol extinction profiles using MAX-DOAS measurements over Athens, Greece

Author

Gratsea, Myrto, primary, Bösch, Tim, additional, Kokkalis, Panos, additional, Richter, Andreas, additional, Vrekoussis, Mihalis, additional, Kazadzis, Stelios, additional, Tsekeri, Alexandra, additional, Papayannis, Alexandros, additional, Mylonaki, Maria, additional, Amiridis, Vassilis, additional, Mihalopoulos, Nikos, additional, and Gerasopoulos, Evangelos, additional

Published
2020
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19. An improved tropospheric NO2 column retrieval algorithm for TROPOMI over Europe.

Author

Liu, Song, Valks, Pieter, Pinardi, Gaia, Xu, Jian, Chan, Ka Lok, Argyrouli, Athina, Lutz, Ronny, Beirle, Steffen, Khorsandi, Ehsan, Baier, Frank, Huijnen, Vincent, Bais, Alkiviadis, Donner, Sebastian, Dörner, Steffen, Gratsea, Myrto, Hendrick, François, Karagkiozidis, Dimitris, Lange, Kezia, Piters, Ankie J. M., and Remmers, Julia

Subjects
AIR quality monitoring, EMISSION inventories, WATER vapor, AIR masses, OPTICAL spectroscopy, NITROGEN dioxide, CHEMICAL models
Abstract

Launched in October 2017, the TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel-5 Precursor provides the potential to monitor air quality over point sources across the globe with a spatial resolution as high as 5.5 km × 3.5 km (7 km × 3.5 km before 6 August 2019). The nitrogen dioxide (NO2) retrieval algorithm for the TROPOMI instrument consists of three steps: the spectral fitting of the slant column, the separation of stratospheric and tropospheric contributions, and the conversion of the slant column to a vertical column using an air mass factor (AMF) calculation. In this work, an improved tropospheric NO2 retrieval algorithm from TROPOMI measurements over Europe is presented. The stratospheric estimation is implemented using the STRatospheric Estimation Algorithm from Mainz (STREAM), which was developed as a verification algorithm for TROPOMI and does not require chemistry transport model data as input. A directionally dependent STREAM (DSTREAM) is developed to correct for the dependency of the stratospheric NO2 on the viewing geometry by up to 2 × 1014 molec/cm2. Applied to synthetic TROPOMI data, the uncertainty in the stratospheric column is 3.5 × 1014 molec/cm2 for polluted conditions. Applied to actual measurements, the smooth variation of stratospheric NO2 at low latitudes is conserved, and stronger stratospheric variation at higher latitudes are captured. For AMF calculation, the climatological surface albedo data is replaced by geometry-dependent effective Lambertian equivalent reflectivity (GE_LER) obtained directly from TROPOMI measurements with a high spatial resolution. Mesoscale-resolution a priori NO2 profiles are obtained from the regional POLYPHEMUS/DLR chemistry transport model with the TNO-MACC emission inventory. Based on the latest TROPOMI operational cloud parameters, a more realistic cloud treatment is provided by a clouds-as-layers (CAL) model, which treats the clouds as uniform layers of water droplets, instead of the clouds-as-reflecting-boundaries (CRB) model, in which clouds are simplified as Lambertian reflectors. For the error analysis, the tropospheric AMF uncertainty, which is the largest source of NO2 uncertainty for polluted scenarios, ranges between 20 % and 50 %, leading to a total uncertainty in the tropospheric NO2 column in the 30-60 % range. From a validation performed with ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, the improved tropospheric NO2 data shows good correlations for nine European urban/suburban stations with an average correlation coefficient of 0.78. The implementation of the algorithm improvements leads to a decrease of the relative difference from −55.3 % to −34.7 % on average. [ABSTRACT FROM AUTHOR]

Published
2021
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20. Evaluation of the LOTOS-EUROS NO2 simulations using ground-based measurements and S5P/TROPOMI observations over Greece.

Author

Skoulidou, Ioanna, Koukouli, Maria-Elissavet, Manders, Astrid, Segers, Arjo, Karagkiozidis, Dimitris, Gratsea, Myrto, Balis, Dimitris, Bais, Alkiviadis, Gerasopoulos, Evangelos, Stavrakou, Trisevgeni, Geffen, Jos van, Eskes, Henk, and Richter, Andreas

Abstract

The evaluation of chemical transport models, CTMs, is essential for the assessment of their performance regarding the physical and chemical parameterizations used. While regional CTMs have been widely used and evaluated over Europe, their validation over Greece is limited. In this study, we investigate the performance of the LOTOS-EUROS v2.2.001 regional chemical transport model in simulating nitrogen dioxide, NO2, over Greece from June to December 2018. In-situ NO2 measurements obtained from the National Air Pollution Monitoring Network are compared with surface simulations over the two major cities of Greece, Athens and Thessaloniki. The model reproduces well the spatial variability of the measured NO2 with a spatial correlation coefficient of 0.85 for the period between June and December 2018. About half of the 14 air quality monitoring stations show a good temporal correlation to the simulations, higher than 0.6, during daytime (12–15 p.m. local time), while the corresponding biases are negative. Most stations show stronger negative biases during winter than in summer. Furthermore, the simulated tropospheric NO2 columns are evaluated against ground-based MAX-DOAS NO2 measurements and space-borne Sentinel 5-Precursor TROPOMI tropospheric NO2 observations in July and December 2018. LOTOS-EUROS captures better the NO2 temporal variability in December (0.61 and 0.81) than in July (0.50 and 0.21) when compared to the corresponding measurements of the MAX-DOAS instruments in Thessaloniki and the rural azimuth viewing direction in Athens respectively. The urban azimuth viewing direction in Athens region however shows a better correlation in July than in December (0.41 and 0.19, respectively). LOTOS-EUROS NO2 columns over Athens and Thessaloniki agree well with the TROPOMI observations showing higher spatial correlation in July (0.95 and 0.82, respectively) than in December (0.82 and 0.66, respectively) while the relative temporal correlations are higher during winter. Overall, the comparison of the simulations with the TROPOMI observations shows a model underestimation in summer and an overestimation in winter both in Athens and Thessaloniki. Updated emissions for the simulations and model improvements when extreme values of boundary layer height are encountered are further suggested. [ABSTRACT FROM AUTHOR]

Published
2020
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21. Retrieval and evaluation of tropospheric aerosol extinction profiles using MAX-DOAS measurements over Athens, Greece.

Author

Gratsea, Myrto, Bösch, Tim, Kokkalis, Panos, Richter, Andreas, Vrekoussis, Mihalis, Kazadzis, Stelios, Tsekeri, Alexandra, Papayannis, Alexandros, Mylonaki, Maria, Amiridis, Vassilis, Mihalopoulos, Nikos, and Gerasopoulos, Evangelos

Subjects
*TROPOSPHERIC aerosols, *URBAN pollution, *OPTICAL spectroscopy, *BIOLOGICAL extinction, *OPTICAL depth (Astrophysics), *LIGHT absorption
Abstract

In this study, we report on the retrieval of aerosol extinction profiles from ground-based scattered sunlight multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements, carried out at Athens, Greece. It is the first time that aerosol profiles are retrieved from MAX-DOAS measurements in Athens. The reported aerosol vertical distributions at 477 nm are derived from the oxygen dimer (O4) differential slant column density observations at different elevation angles by applying the BOREAS retrieval algorithm. Four case studies have been selected for validation purposes; the retrieved aerosol profiles and the corresponding aerosol optical depths (AODs) from the MAX-DOAS are compared with lidar extinction profiles and with sun photometric measurements (AERONET observations), respectively. Despite the different approach of each method regarding the retrieval of the aerosol information, the comparison with the lidar measurements at 532 nm reveals a very good agreement in terms of vertical distribution, with r > 0.85 in all cases. The AODs from the MAX-DOAS and the sun-photometer (the latter at 500 nm) show a satisfactory correlation (with r ≈ 0.6 in three out of the four cases). The comparison indicates that the MAX-DOAS systematically underestimates the AOD in the cases of large particles (small Ångström exponent) and for measurements at small relative azimuthal angles between the viewing direction and the Sun. Better agreement is achieved in the morning, at large relative azimuthal angles. Overall, the aerosol profiles retrieved from MAX-DOAS measurements are of good quality; thus, new perspectives are opened up for assessing urban aerosol pollution on a long term-basis in Athens from continuous and uninterrupted MAX-DOAS measurements. [ABSTRACT FROM AUTHOR]

Published
2020
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22. GARRLiC and LIRIC: strengths and limitations for the characterization of dust and marine particles along with their mixtures

Author

Tsekeri, Alexandra, primary, Lopatin, Anton, additional, Amiridis, Vassilis, additional, Marinou, Eleni, additional, Igloffstein, Julia, additional, Siomos, Nikolaos, additional, Solomos, Stavros, additional, Kokkalis, Panagiotis, additional, Engelmann, Ronny, additional, Baars, Holger, additional, Gratsea, Myrto, additional, Raptis, Panagiotis I., additional, Binietoglou, Ioannis, additional, Mihalopoulos, Nikolaos, additional, Kalivitis, Nikolaos, additional, Kouvarakis, Giorgos, additional, Bartsotas, Nikolaos, additional, Kallos, George, additional, Basart, Sara, additional, Schuettemeyer, Dirk, additional, Wandinger, Ulla, additional, Ansmann, Albert, additional, Chaikovsky, Anatoli P., additional, and Dubovik, Oleg, additional

Published
2017
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