Aqueous Multiphase Chemistry of Organic Aerosols in Humid Urban Environments

Description

Aerosol pollution has negative impacts on air quality and climate. Organic aerosols are a ubiquitous component of the submicron aerosol fraction. Atmospheric condensed-phase water (e.g., aerosol water, cloudwater) is increasingly recognized to play an important role in the formation and oxidation of organic aerosols. Water-soluble organic gases (WSOGs) partition into the condensed phase, where they undergo aqueous-phase reactions to form aqueous secondary organic aerosols (aqSOA). The photolysis of light-absorbing organic matter in aqueous droplets and aerosols can produce aqueous-phase photooxidants (e.g., 1O2, OHradials), which can rapidly oxidize aqueous organic aerosols. Aerosol water modifies the aerosol phase and viscosity, which will alter heterogeneous reaction rates and pathways that oxidize aqueous organic aerosols after initial formation or emission. Studies have shown that one main reason why atmospheric models cannot capture ambient observations of organic aerosols is due to our incomplete knowledge of aqueous multiphase organic aerosol chemistry.This proposed research aims to provide new scientific insights into the aqueous multiphase chemistry that form and oxidize organic aerosols in humid urban environments. First, we will characterize anthropogenic WSOGs and their aqueous-phase reactions that formaqSOA. WSOGs will be scrubbed from ambient air into deionized water using a mist chamber at an urban site in Hong Kong. Aqueous photooxidation experiments simulating aqSOA formation reactions in atmospheric cloudwater will be conducted on these aqueous samples. We will use different analytical techniques (e.g., liquid chromatography-mass spectrometry, ion chromatography) to identify and quantify major constituents in these aqueous samples, which will be used to elucidate scrubbed WSOGs, oxidation products, and aqueous-phase reaction mechanisms that form aqSOA. Second, we will measure various aqueous-phase photooxidants formed from the photolysis of ambient aqueous aerosols sampled from an urban site in Hong Kong. We will characterize light-absorption roperties, and quantify the concentrations of aqueous-phase 1O2 and OH formed photolytically in ambient aqueous aerosol samples. Third, we will investigate how anthropogenic inorganic gas-phase pollutants NOx and SO2 affect the heterogeneous oxidation of aqueous rganic aerosols by conducting systematic laboratory oxidation experiments on ambient aerosol samples and laboratory-generated modelorganic aerosols. The successful implementation of this proposal will fill critical knowledge gaps on the aqueous multiphase chemistry of organic aerosols in humid urban environments. Outputs of this proposed research include measured reaction rate constants, kinetics, lifetimes, and reaction mechanisms, which are useful inputs for atmospheric models used to formulate air quality policies in humid subtropical cities such as Hong Kong.