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. Global mapping of satellite tropospheric NO2 vertical columndensity (VCD), a key gas in air quality monitoring, requires accurateretrievals over complex urban and industrialized areas and under anyatmospheric conditions. The high abundance of aerosol particles in regionsdominated by anthropogenic fossil fuel combustion, e.g. megacities, and/orbiomass-burning episodes, affects the space-borne spectral measurement.Minimizing the tropospheric NO2 VCD biases caused by aerosolscattering and absorption effects is one of the main retrieval challengesfrom air quality satellite instruments. In this study, the reference OzoneMonitoring Instrument (OMI) DOMINO-v2 product was reprocessed over cloud-freescenes, by applying new aerosol correction parameters retrieved from the477 nm O2−O2 band, over eastern China and South America for 2 years(2006–2007). These new parameters are based on two different and separatealgorithms developed during the last 2 years in view of an improved use ofthe OMI 477 nm O2−O2 band: the updated OMCLDO2 algorithm, which derives improved effective cloudparameters, the aerosol neural network (NN), which retrieves explicit aerosolparameters by assuming a more physical aerosol model. The OMI aerosol NN is a step ahead of OMCLDO2 because it primarily estimates anexplicit aerosol layer height (ALH), and secondly an aerosol opticalthickness τ for cloud-free observations. Overall, it was found that allthe considered aerosol correction parameters reduce the biases identified inDOMINO-v2 over scenes in China with high aerosol abundance dominated by finescattering and weakly absorbing particles, e.g. from[ - 20 % : - 40 % ] to[ 0 %:20 % ] in summertime. The use of the retrieved OMI aerosolparameters leads in general to a more explicit aerosol correction and highertropospheric NO2 VCD values, in the range of [ 0 %:40 % ], thanfrom the implicit correction with the updated OMCLDO2. This number overallrepresents an estimation of the aerosol correction strategy uncertaintynowadays for tropospheric NO2 VCD retrieval from space-borne visiblemeasurements. The explicit aerosol correction theoretically includes a morerealistic consideration of aerosol multiple scattering and absorptioneffects, especially over scenes dominated by strongly absorbing particles,where the correction based on OMCLDO2 seems to remain insufficient. However,the use of ALH and τ from the OMI NN aerosol algorithm is not astraightforward operation and future studies are required to identify theoptimal methodology. For that purpose, several elements are recommended inthis paper. Overall, we demonstrate the possibility of applying a more explicitaerosol correction by considering aerosol parameters directly derived fromthe 477 nm O2−O2 spectral band, measured by the same satelliteinstrument. Such an approach can, in theory, easily be transposed to thenew-generation of space-borne instruments (e.g. TROPOMI on board Sentinel-5Precursor), enabling a fast reprocessing of tropospheric NO2 dataover cloud-free scenes (cloudy pixels need to be filtered out), as well asfor other trace gas retrievals (e.g. SO2 , HCHO ).

atmospheric measurement techniques

Minimizing aerosol effects on the OMI tropospheric NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; retrieval – An improved use of the 477 nm O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; − O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; band and an estimation of the aerosol correction uncertainty