Dual Carbon Isotope-Based Source Apportionment and Light Absorption Properties of Water-Soluble Organic Carbon in PM2.5 Over China

Water-soluble organic carbon (WSOC) makes up a large fraction of organic carbon, which has attracted considerable attention due to its light absorption properties and effects on human health. However, the poorly constrained sources and light absorption properties of WSOC give rise to large uncertainties in its effects on climate and health, especially in regions with high pollutant loading. Here, we investigated the sources and light absorption properties of WSOC in 10 cities across China by dual carbon isotope analysis and UV-visible spectrophotometry, respectively. Despite a dominant contribution of nonfossil sources, the fossil source contribution to WSOC was higher in China than in other regions of the world. The average mass absorption efficiency of WSOC at 365 nm (MAE(365)) the fossil source contribution of WSOC were 1.13 0.37 m(2)/gC and 39.9 9.4%, respectively; both values were higher in northern than southern China. The nonfossil source contribution and delta C-13 of WSOC exhibited significant seasonal variations, with higher values in cold seasons, likely in association with enhanced corn residue burning. In addition, higher MAE(365) in the cold seasons (fall and winter) was strongly related to enhanced biomass burning emissions. However, the fossil source contribution of WSOC showed a positive relationship with MAE(365) in the cold seasons. This may be because the primary fossil WSOC emitted directly by coal combustion and the secondary fossil WSOC generated under the high NOx conditions in the cold seasons would enhance the color of the entire WSOC. To limit the impacts of WSOC on regional climate and human health, it is suggested that mitigation strategies should consider spatiotemporal variation in WSOC sources, its light absorption properties, and the various formation pathways. Key Points The fossil fuel contribution and corresponding MAE(365) value of water-soluble organic carbon (WSOC) were higher in northern than southern China Higher C-14 and C-13 of WSOC in cold seasons may be related to corn residue burning Primary coal combustion emissions and secondary fossil WSOC generated under high NOX conditions increase MAE(365) of WSOC in cold seasons

Automated summary

The study found that the contribution of fossil fuel to water-soluble organic carbon (WSOC) and its corresponding MAE(365) was higher in northern China than southern China; higher C-14 and C-13 of WSOC in the cold seasons may be related to corn residue burning; in the cold seasons, primary coal combustion emissions and secondary fossil WSOC generated under high NOx conditions increase the MAE(365) of WSOC.