The Role of Naphthalene and Its Derivatives in the Formation of Secondary Organic Aerosols in the Yangtze River Delta Region, China

Abstract. Naphthalene (Nap) and its derivatives, including 1-methylnaphthalene (1-MN) and 2-methylnaphthalene (2-MN), serve as prominent intermediate volatile organic compounds (IVOCs) contributing to the formation of secondary organic carbon (SOC). In this study, the Community Multi-Scale Air Quality (CMAQ) model coupled with detailed emissions and reactions of these compounds was utilized to examine their roles in the formation of SOC and other secondary pollutants in the Yangtze River Delta (YRD) region during summer. Remarkably, significant underestimations of Nap and MN concentrations (by 79 % and 85 %) were observed at the Taizhou site. To better capture the temporal variations of Nap and MN, their emissions in the YRD region were scaled up by a factor of 5 and 7, respectively, with constraints based on field measurements. After adjusting their emissions, Nap concentrations reached 27 ppt in the YRD, accounting for 4.1 % and 9.1 % (up to 13.7 %) of total aromatics emissions and aromatic-derived SOC, respectively. 1-MN and 2-MN were relatively low, with an average of 3 and 6 ppt in the YRD, and contributed 3.1 % of aromatic-derived SOC. The influences of Nap and MN oxidation on ozone and radicals might be trivial on a regional scale but were not negligible when considering daily fluctuations, particularly in Shanghai and Suzhou. This study emphasizes the high SOC formation potentials of Nap and MN, which may pose environmental risks and adverse health.