OMI-observed HCHO in Shanghai, China, during 2010–2019 and ozone sensitivity inferred by an improved HCHO ∕ NO<sub>2</sub> ratio

Abstract. In recent years, satellite remote sensing has been increasingly used in the long-term observation of ozone (O3) precursors and its formation regime. this work, formaldehyde (HCHO) data from Ozone Monitoring Instrument (OMI) were to analyze temporal spatial distribution HCHO vertical column densities (VCDs) Shanghai 2010 2019. VCDs exhibited highest value summer lowest winter, high VCD being concentrated western Shanghai. Temperature largely influences by affecting biogenic emissions photochemical reactions, industry was major anthropogenic source. The satellite-observed formaldehyde-to-nitrogen dioxide ratio (FNRSAT) reflects that O3 regime had significant seasonal characteristics gradually manifested as a transitional dominating uneven space mainly reflected higher FNRSAT surface concentration suburban areas. To compensate for shortcoming it can only characterize around overpass time, correction implemented with hourly FNR data. After correction, showed trend moving towards VOC-limited both time space, indicated better reflect day. This study help us understand regimes also provide method improve characterizing day, which will be developing prevention control strategies.