Chemical Composition and Origin of Water Soluble HUmic-Like Substances (HULISWS) in Atmospheric Aerosols in the Pearl River Delta Region

HUmic Like Substances (HULIS) are considered as an important contributor to organic matter in fine aerosols. The water soluble HULIS (HULISWS) component is estimated to account for 43-67% of water soluble organic matter (WSOM) in fine aerosols in the Pearl River Delta (PRD) region in South China. However, HULIS is normally considered as an unresolved mixture and little is known about its detailed molecular composition and formation pathways in the atmosphere. In this project, we propose to characterize the chemical structures of HULISWS species in about 240 PM2.5 aerosol samples collected at four strategically-located sites in PRD during a one-year period using gas chromatography mass spectrometry, and liquid chromatographic techniques couples to ion trap and high-resolution time-of-flight mass spectrometry. Their temporal and spatial variations and relationship with the major aerosol constituent will be investigated as well. Our preliminary results show that aromatic carboxylic acids (including hydroxyl benzoic, methoxy hydroxyl benzoic, and benzene-di- and tri-carboxylic acids), aliphatic carboxylic acids (including secondary organic aerosol tracers of biogenic hydrocarbons), and organosulfates are the main three groups of HULISWS compounds identified in PM2.5 aerosol samples. This suggests that automobile exhaust, biomass burning, and secondary formation are important contributors to HULISWS in ambient aerosols in the region. Results from this study will provide insight on the chemical composition and origin of HULISWS in the PRD region. Such information is essential for us to investigate the influence of HULISWS on the hygroscopicity, optical properties, and toxicity of ambient fine aerosols, and the resulting adverse effect of fine particulates on visibility and human health.