Linking the Physicochemical Properties of Brown Carbon to the Production of Singlet Oxygen and Organic Triplets Excited States in Atmospheric Aqueous PM2.5
THEODORA NAH, Yuting Lyu, Yitao Li, Ruihan Ma, Tianye Zhou, City University of Hong Kong
Abstract Number: 311
Working Group: Aerosol Chemistry
Abstract
Aqueous photooxidants such as singlet oxygen (1O2*) and organic triplet excited states (3C*) are known to drive many chemical processes in atmospheric waters. While it is widely recognized that the photoexcitation of brown carbon (BrC) in atmospheric aqueous aerosols can lead to the photochemical production of 1O2* and 3C*, the physicochemical properties of BrC that govern the production of these photooxidants remain poorly understood. Here, we combined 1O2* and 3C* measurements of aqueous PM2.5 collected during different seasons and in different parts of Hong Kong, South China with corresponding measurements of the physicochemical properties of the aqueous BrC, and applied various statistical tools and non-negative matrix factorization (NMF) to link the BrC physicochemical properties to 1O2* and 3C* production. Three fluorescent components, less oxygenated compounds from biomass burning, highly oxygenated compounds, and aromatic derivatives, were identified in aqueous BrC. NMF attributed >85 % of wintertime 3C* production to biomass-burning BrC, while summer 1O2* production was attributed to aged marine aerosols. Spearman correlations revealed strong associations between 1O2* concentrations and absorption coefficients (e.g., α300), while 3C* correlated with aromaticity proxies (e.g., S275-295). Multiple linear regression revealed that α254 and biological index (BIX) could be used to predict 1O2* (r² = 0.95) and 3C* (r² = 0.77) concentrations, respectively, thus indicating that the photochemical production of photooxidants in atmospheric waters could be predicted using measurable BrC physicochemical properties.