Abstract
Abstract. In recent years, satellite remote sensing has been increasingly used in the long-term observation of ozone (O3) precursors and its formation regime. In this work, formaldehyde (HCHO) data from Ozone Monitoring Instrument (OMI) were used to analyze the temporal and spatial distribution of HCHO vertical column densities (VCDs) in Shanghai from 2010 to 2019. HCHO VCDs exhibited the highest value in summer and the lowest in winter, the high VCD being concentrated in western Shanghai. Temperature largely influences HCHO by affecting the biogenic emissions and photochemical reactions, and industry was the major anthropogenic source. The satellite-observed formaldehyde-to-nitrogen dioxide ratio (FNRSAT) reflects that the O3 formation regime had significant seasonal characteristics and gradually manifested as a transitional ozone formation regime dominating in Shanghai. The uneven distribution in space was mainly reflected in the higher FNRSAT and surface O3 concentration in suburban areas. To compensate for the shortcoming of FNRSAT that it can only characterize O3 formation around satellite overpass time, correction of FNRSAT was implemented with hourly surface FNR and O3 data. After correction, the O3 formation regime showed the trend moving towards being VOC-limited in both time and space, and the regime indicated by FNRSAT can better reflect O3 formation for a day. This study can help us better understand HCHO characteristics and O3 formation regimes in Shanghai and also provide a method to improve FNRSAT for characterizing O3 formation in a day, which will be significant for developing O3 prevention and control strategies.
Highlights
Formaldehyde (HCHO) is an important trace gas in the atmosphere
HCHO vertical column densities (VCDs) decreased from the highest value of 12.78 × 1015 molec. cm−2 in 2010 to the lowest value of 10.37 × 1015 molec. cm−2 in 2012, rebounded from 2012 to 2014, and fluctuated slightly in the following years (Fig. 1a)
The HCHO VCDs varied with the season, with the maxima and minima corresponding to the respective summer (June, July, and August) and winter (December, January, and February) and moderate levels in spring (March, April, and May) and autumn (September, October, and November) (Fig. 1c)
Summary
Formaldehyde (HCHO) is an important trace gas in the atmosphere. It has an irritating effect on human eyes, skin, and respiratory mucosa and can cause cancer in high concentration Atmospheric HCHO is an intermediate product of almost all volatile organic compound (VOC) oxidation, it can be indicative of the overall VOC level (Chan et al, 2019). HCHO can be emitted through anthropogenic sources, biogenic sources, and biomass combustion. Anthropogenic sources like transportation, power, industry, and residential emissions increase the amount of HCHO by emitting VOCs into the atmosphere (Wang et al, 2017). Biogenic volatile organic compounds (BVOCs) are important sources of HCHO. The removal of HCHO is mainly through photolysis, reaction with OH radicals, and the deposition (Ling et al, 2016; Xing et al, 2020)
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