Photochemical loss and source apportionment of atmospheric volatile organic compounds in a typical basin city of the Chengdu-Chongqing Economic Circle

Abstract

Volatile organic compounds (VOCs) are key precursors in ozone formation, and their photochemical losses during atmospheric transport critically influence pollution characterization and source apportionment. The Chengdu-Chongqing region experiences heightened ozone pollution during the summer months. In light of this, we conducted an in-depth analysis of the atmospheric concentrations and photochemical losses of 56 VOC species in Rongchang of Chongqing, a representative city within the Chengdu-Chongqing Economic Circle from June to September 2023. We employed a combination of Positive matrix factorization and backward trajectory analysis to comprehensively resolve emission sources. The results indicate that not considering photochemical losses could lead to substantial underestimations in VOC concentrations (TVOC, 20.87 %), ozone formation potential (OFP, 27.40 %) and hydroxyl radical loss (L_OH, 56.20 %). Positive matrix factorization (PMF) analysis, based on the initial and observed concentrations, revealed that the motor vehicle emissions are overestimated by 7.95 % if neglecting the photochemical losses. Conversely, the industrial emissions, natural emissions, fossil fuel combustion, and solvent use sources are underestimated by 70.49 %, 44.24 %, 13.02 %, and 25.07 %, respectively. Backward trajectory analysis identified that industrial emissions predominantly originated from southeastern Sichuan and southwestern Chongqing, while solvent use emissions were concentrated in the main urban area of Chongqing. This study quantifies the impact of photochemical reactions on the characterization of atmospheric VOCs and source apportionment in Chongqing. The results provide critical insights to inform more effective control strategies for VOC pollution in the Chengdu-Chongqing metropolitan area.