Insights into dissolved organics in non-urban areas - Optical properties and sources

Brown carbon aerosols show obvious light absorption properties in the ultraviolet–visible (UV–Vis) range, which has an important impact on photochemistry and climate. In this study, experimental samples originated from the North slope of the Qinling Mountains (at two remote suburb sites) to study the optical properties of water-soluble brown carbon (WS–BrC) in PM2.5. The WS-BrC of TY (a sampling site on the edge of Tangyu of Mei county) has a stronger light absorption ability than CH (a rural sampling site, near the Cuihua Mountains scenic spot). The direct radiation effect of WS-BrC relative to elemental carbon (EC) is 6.67 ± 1.36% in TY and 24.13 ± 10.84% in CH in the UV range, respectively. In addition, two humic-like and one protein-like fluorophore components in WS-BrC were identified by fluorescence spectrum and parallel factor (EEMs-PARAFAC). Humification index (HIX), biological index (BIX) and fluorescence index (FI) together showed that the WS-BrC in the two sites may originate from fresh aerosol emissions. Potential source analysis of Positive Matrix Factorization (PMF) model show that the combustion process, vehicle, secondary formation and road dust are the main contributors to WS-BrC.