Significant Secondary Organic Aerosol Production From Aqueous-phase Processing Of Intermediate Volatility Organic Compounds

Secondary organic aerosols(SOA)are important components in the atmospheric fine particulate matter,mainly composed of volatile organic compounds(VOCs)or medium/semivolatile organic compounds(S/IVOCs)emitted by anthropogenic or natural sources through gas-phase oxidation or liquid-phase oxidation.SOA are solids or liquids suspended in the atmosphere generated by processes such as gas/particle partitioning.Over the past two decades,volatile organic compounds(VOCs)have received widespread attention in research,mainly for huge emissions on a global scale.The volatile organic compounds(IVOCs)have been rising in recent years and been identified as important air pollutants recently.IVOCs play an important role in the formation of SOA in gas phase reaction.However,SOA derived from IVOC by liquid phase oxidation has not been investigated in depth.In this study,we selected three IVOC simulated liquid phase processes,dibenzothiophene(DBT),phenanthrene(PHE)and naphthoquinone(NAQ)with two oxidants,3,4-dimethoxybenzaldehyde(providing 3C*)and hydrogen peroxide(providing ·OH).High performance liquid chromatograph(HPLC),UV visible spectrophotometer(UV-vis)and total organic carbon analyzer(TOC)were used for off-line experiments to analyze the degradation process kinetics and light absorption of products.Mass spectra,elemental ratios,and SOA yields were analyzed online using black carbon aerosol mass spectrometry(SP-AMS).DBT,PHE and NAQ can be degraded in the liquid phase with oxidants under light and dark reaction conditions.The calculation of absorbance and MAE365 also demonstrates that the liquid phase oxidation reactions of these three IVOCs are likely to be an important source of atmospheric brown carbon.Finally,through high-resolution mass spectra and element ratio analysis,the oxidative product formed in the liquid phase process indicates that the liquid phase process of IVOC plays an important role in SOA in the real atmosphere.