Preprints
https://doi.org/10.5194/amt-2022-319
https://doi.org/10.5194/amt-2022-319
 
02 Dec 2022
02 Dec 2022
Status: this preprint is currently under review for the journal AMT.

Evaluating the effects of columnar NO2 on the accuracy of aerosol optical properties retrievals

Theano Drosoglou1, Ioannis-Panagiotis Raptis1,2, Massimo Valeri3, Stefano Casadio3, Francesca Barnaba4, Marcos Herreras-Giralda5, Anton Lopatin5, Oleg Dubovik6, Gabriele Brizzi7, Fabrizio Niro7, Monica Campanelli4, and Stelios Kazadzis8 Theano Drosoglou et al.
  • 1Institute for Environmental Research and Sustainable Development, National Observatory of Athens (IERSD/NOA), 15236 Athens, Greece
  • 2Laboratory of Climatology and Atmospheric Environment, Sector of Geography and Climatology, Department of Geology and Environment, National and Kapodistrian University of Athens, Athens, GR-15784, Greece
  • 3Serco Italia S.p.A., Frascati, Rome, Italy
  • 4National Research Council, Institute of Atmospheric Sciences and Climate, CNR- ISAC, National Research Council, Rome, Italy
  • 5GRASP SAS, Remote Sensing Developments, 59260 Lezennes, France
  • 6Univ. Lille, CNRS, UMR 8518 - LOA - Laboratoire d’Optique Atmosphérique, Lille, France
  • 7ESA-ESRIN, Frascati, Rome, Italy
  • 8Physicalisch-Meteorologisches Observatorium Davos, World Radiation Center, CH-7260 Davos, Switzerland

Abstract. We aim to evaluate the NO2 absorption effect in aerosol properties derived from sun-sky radiometers as well as the possible retrieval algorithm improvements by using more accurate characterization of NO2 optical depth. For this purpose, we employ multiannual (2017–2022) records of Aerosol Optical Depth (AOD), Ångström Exponent (AE) and Single Scattering Albedo (SSA) collected by sun photometers at an urban and a suburban site in the Rome area (Italy) in the framework of both the AERONET and SKYNET networks. The uncertainties introduced in the retrievals by the NO2 absorption are investigated using high-frequency observations of total NO2 derived from co-located Pandora spectroradiometer systems as well as space-borne NO2 products from the Tropospheric Monitoring Instrument (TROPOMI). The correction is useful for lower AODs (< 0.3), where the majority of observations is found, especially under high NO2 pollution events. The analysis does not reveal any significant impact of the NO2 correction on the derived aerosol temporal trends for the very limited data sets used in this study. However, the effect is expected to become more evident for trends derived from larger data sets as well as in the case of an important NO2 trend. In addition, the comparisons of the NO2-modified ground-based AOD data with satellite retrievals from the Deep Blue (DB) algorithm of the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) resulted in a slight improvement in the agreement of about 0.003 and 0.006 for AERONET and SKYNET, respectively. Finally, the uncertainty in assumptions of NO2 seem to have a non-negligible impact on the retrieved values of SSA at 440 nm leading to an average positive bias of 0.02 (2.5 %) in both locations for high NO2 loadings (> 0.9 DU).

Theano Drosoglou et al.

Status: open (until 11 Feb 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-319', Anonymous Referee #1, 19 Jan 2023 reply
  • RC2: 'Comment on amt-2022-319', Anonymous Referee #2, 29 Jan 2023 reply

Theano Drosoglou et al.

Theano Drosoglou et al.

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Short summary
Aerosol optical properties derived from sun-photometers depend on the optical depth of trace gases absorbing solar radiation at specific spectral ranges. Various networks use satellite-based climatologies to account for this or neglect their effect. In this work, we evaluate the effect of NO2 absorption in aerosol retrievals from AERONET and SKYNET over two stations in Rome, Italy, with relatively high NO2 spatiotemporal variations, using NO2 data from the Pandora network and the TROPOMI sensor.