10.1021/acs.est.8b04523.s001 Guancong Huang Guancong Huang Ying Liu Ying Liu Min Shao Min Shao Yue Li Yue Li Qi Chen Qi Chen Yan Zheng Yan Zheng Zhijun Wu Zhijun Wu Yuechen Liu Yuechen Liu Yusheng Wu Yusheng Wu Min Hu Min Hu Xin Li Xin Li Sihua Lu Sihua Lu Chenjing Wang Chenjing Wang Junyi Liu Junyi Liu Mei Zheng Mei Zheng Tong Zhu Tong Zhu Potentially Important Contribution of Gas-Phase Oxidation of Naphthalene and Methylnaphthalene to Secondary Organic Aerosol during Haze Events in Beijing American Chemical Society 2019 Important Contribution Phthalic anhydride F p Beijing Naphthalene MN Gas-Phase Oxidation particle phase contribution  of Nap generation product gas-phase photooxidation products aerosol phase precursor consumption-based methods 2- ring PAHs OA mass loadings SOA formation Secondary Organic Aerosol tracer product-based phthalic anhydride 2016 winter Proton Transfer Reaction-Quadrupole interface Time-of-Flight Mass Spectrometer high-NO x conditions laboratory chamber experiments ambient SOA Haze Events 2- formylcinnamaldehyde wintertime haze 2019-01-09 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Potentially_Important_Contribution_of_Gas-Phase_Oxidation_of_Naphthalene_and_Methylnaphthalene_to_Secondary_Organic_Aerosol_during_Haze_Events_in_Beijing/7624301 Naphthalene (Nap) and methylnaphthalene (MN) are the most abundant polycyclic aromatic hydrocarbons (PAHs) in atmosphere and have been proposed to be important precursors of anthropogenic secondary organic aerosol (SOA) derived from laboratory chamber experiments. In this study, atmospheric Nap/MN and their gas-phase photooxidation products were quantified by a Proton Transfer Reaction-Quadrupole interface Time-of-Flight Mass Spectrometer (PTR-QiTOF) during the 2016 winter in Beijing. Phthalic anhydride, a late generation product from Nap under high-NO<sub><i>x</i></sub> conditions, appeared to be more prominent than 2-formylcinnamaldehyde (early generation product), possibly due to more sufficient oxidation during the haze. 1,2-Phthalic acid (1,2-PhA), the hydrated form of phthalic anhydride, was capable of partitioning into aerosol phase and served as a tracer to explore the contribution of Nap to ambient SOA. The measured fraction in particle phase (<i>F</i><sub>p</sub>) of 1,2-PhA averaged at 73 ± 13% with OA mass loadings of 52.5–87.8 μg/m<sup>3</sup>, lower than the value predicted by the absorptive partitioning model (100%). Using tracer product-based and precursor consumption-based methods, 2-ring PAHs (Nap and MN) were estimated to produce 14.9% (an upper limit) of the SOA formed in the afternoon during the wintertime haze, suggesting a comparable contribution of Nap and MN with monocyclic-aromatics on urban SOA formation.