The importance of photochemical loss to source analysis and ozone formation potential: Implications from in-situ observations of volatile organic compounds (VOCs) in Guangzhou, China

Abstract

The chemical loss of volatile organic compounds (VOCs) is influenced by atmospheric and is closely related to the photochemical formation of ozone (O3). Therefore, research on the atmospheric chemical transformation of VOCs is essential to understand their contribution to O3 formation. This study collected data on photochemical-related atmospheric components and meteorological factors in spring at a typical comprehensive observation platform in Guangzhou, China. The photochemical age method was used to evaluate the loss of VOCs due to atmospheric photochemical transformation and to analyze the contribution of such transformation to the source apportionment of VOCs and to the ozone formation potential (OFP). The results show that the mean photochemical loss of total volatile organic compounds (TVOCs) during the observation period was 4.1 ppbv, accounting for approximately 15% of the initial TVOC content. Alkenes had the highest consumed concentration/initial concentration (C/I ratio) of 37.3%. A comparison of the source apportionment results obtained using observational positive matrix factorization (Ob-PMF) and in situ positive matrix factorization (In-PMF) revealed that photochemical losses significantly affected VOCs emitted from industrial and biological sources. Furthermore, neglecting the photochemical loss of VOCs in PMF source apportionment could lead to an underestimation of the contribution of VOCs from industrial and biological sources. The calculated values of OFP under VOC loss (OFPC–VOCs) showed that OFPC-VOCs constituted approximately 30% of the OFP of the initial VOCs. 93.2% of the OFP was attributed to the photochemical loss of alkenes and aromatic hydrocarbons, indicating their significant influence on O3 formation. This study emphasizes the importance of fully considering the photochemical loss of VOCs for accurately assessing their sources and contributions to ozone pollution. It also provides theoretical support for formulating VOC emission reduction strategies in the Pearl River Delta region.