Sources and budget analysis of ambient formaldehyde in the east-central area of the yangtze River Delta region, China

Abstract

Ambient formaldehyde (HCHO) is not only the intermediate product of volatile organic compounds (VOCs) oxidation but also the precursor of radicals and ozone (O3). In this study, sources, production, and destruction pathways of ambient HCHO were investigated based on online observation of ambient HCHO and offline measurement of VOCs in the east-central area of the Yangtze River Delta (YRD) region from August 31st to October 5th, 2021. The abundance and variation characteristics of HCHO were analyzed, and then the sources of HCHO were apportioned using the multiple linear regression method (MLR), positive matrix factorization (PMF) model, and the observation-based 0-dimension box model coupled with the master chemical mechanism (OBM-MCM). The results of MLR, PMF, and OBM-MCM suggested that secondary production was the largest contributor to HCHO concentration, especially for non-attainment days of O3 during which the average relative contribution of secondary production to HCHO reached 80%. The main production and destruction pathways of HCHO (budget analysis) and key precursors of HCHO production were explored using the OBM-MCM. The budget analysis results suggested that reactions of alkoxyl radicals with oxygen (O2) (i.e. CH3O + O2 and RO + O2) were the main production pathways for HCHO, while photolysis and reaction with OH radical were the main destruction pathways for HCHO. The production of HCHO was sensitive to isoprene, trans-2-butene, ethylene, cis-2-butene, 1,2,4-trimethylbenzene, m/p-xylene, styrene, 1,2,3-trimethylbenzene, propene, and 1,2,4-trimethylbenzene. These results obtained in this study are helpful for understanding sources and chemical transformation of ambient HCHO in the YRD region and providing scientific support for the prevention and control of HCHO.