Light-absorption and fluorescence fingerprinting characteristics of water and methanol soluble organic compounds in PM2.5 in cold regions of Northeast China

Abstract

High-performance liquid chromatography-size exclusion chromatography and excitation-emission matrix (EEM) fluorescence spectroscopy were used to analyze the seasonal variations and potential sources of molecular weight (MW) separated light-absorbing chromophores and fluorophores of water-soluble organic compounds (WSOC) and methanol-soluble organic compounds (MSOC) in PM2.5 in cold areas of northern China. The results showed that the light-absorbing organics in MSOC had larger weight-average MW (Mw) (3.19 kDa) and number-average MW (Mn) (1.13 kDa) compared with WSOC (Mw: 1.41 kDa, Mn: 0.692 kDa). The light-absorption of organics showed a trend of winter>spring>autumn>summer and increased on air pollution days. Three fluorescent components including humic-like, protein-like, and terrestrial humic-like components in WSOC were extracted by parallel factor analysis (PARAFAC). Fluorophores in WSOC were dominated by humic-like and terrestrial humic-like components (67.7%). Three fluorescent components extracted from MSOC were low oxidation humic-like, polycyclic aromatic hydrocarbon (PAH)-like, and protein-like components respectively. It is worth noting that compared with WSOC, MSOC may have a higher human health risk due to the presence of PAH-like components. The combination of PARAFAC and self-organizing map had the potential to identify potential sources of fluorophores. It provided a new perspective for comprehensively exploring the characteristics of fluorophores in aerosols. This study provided a reference for further understanding the chemical composition and optical properties of organic aerosols in the cold regions of northern China.