Oxygenated organic molecules (OOMs) in the megacities of east China

Oxygenated organic molecules (OOMs) are critical intermediates connecting the oxidation of volatile organic compounds (VOCs) and the formation of secondary organic aerosol (SOA). However, directly measuring these intermediate vapors presents significant challenges, particularly in megacity areas, due to their exceedingly low concentrations and complex compositional diversity. Since 2018, we have been monitoring OOMs at the SORPES station in Nanjing, eastern China, using a nitrate-CI-APi-ToF. To manage and simplify the complex mass spectra, we employed both binPMF and sub-range binPMF techniques prior to peak fitting, successfully identifying over 2,000 distinct OOM molecules with high accuracy. We also developed a framework to identify probable precursors of the detected OOMs. Our findings indicate that the oxidation of anthropogenic VOCs primarily drives OOM formation across most seasons, contributing approximately 40% each from aromatic compounds and aliphatic hydrocarbons, mainly alkanes. During summer, however, the oxidation of biogenic VOCs significantly contributes OOM production. The irreversible condensation of these OOMs substantially contributes to the growth of newly formed particles and the generation of SOA, particularly under warmer season and highly polluted conditions.