Chemical characterization of oxygenated organic compounds in gas-phase and particle-phase using iodide-CIMS with FIGAERO in urban air

Abstract. The characterization of oxygenated organic compounds in urban areas remains a pivotal gap in our understanding of the evolution of organic carbon under polluted environments, as the atmospheric processes involving interactions between organics and inorganics, anthropogenic pollutants and natural emissions lead to formation of various and complex secondary products. Here, we describe measurements of an iodide chemical ionization time-of-flight mass spectrometer installed with a Filter Inlet for Gases and AEROsols (FIGAERO-I-CIMS) in both gas-phase and particle-phase at an urban site in Guangzhou, a typical mega-city in southern China, during the autumn of 2018. Abundant oxygenated organic compounds containing 2~5 oxygen atoms were observed, including organic acids, multi-functional organics typically emitted form biomass burning, oxidation products of biogenic hydrocarbons and aromatics. Photochemistry played dominant roles in the formation of gaseous organic acids and isoprene-derived organic nitrates, while nighttime chemistry contributed significantly to the formation monoterpene-derived organic nitrates and inorganics. Nitrogen-containing organic compounds occupied a significant fraction of the total signal in both gas and particle phases, with elevated fractions at higher molecular weights. Measurements of organic compounds in particle phase by FIGAERO-I-CIMS explained 24 % of the total organic aerosol mass measured by aerosol mass spectrometer (AMS), and the fraction increased for more aged organic aerosol. The systematically interpretation of mass spectra of the FIGAERO-I-CIMS in urban of Guangzhou provides a holistic view of numerous oxygenated organic compounds in the urban atmosphere, which can serve as a reference for the future field measurements by FIGAERO-I-CIMS in polluted urban regions.