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Anthropogenic Emission Sources of Sulfate Aerosols in Hangzhou, East China: Insights from Isotope Techniques with Consideration of Fractionation Effects between Gas-to-Particle Transformations.

Sulfate (SO42-) is a major species in atmospheric fine particles (PM2.5), inducing haze formation and influencing Earth's climate. In this study, the δ34S values in PM2.5 sulfate (δ34S-SO42-) were measured in Hangzhou, east China, from 2015 September to 2016 October. The result showed that the δ34S-SO42- values varied from 1.6 to 6.4‰ with the higher values in the winter. The estimated fractionation factor (α34Sg→p) from SO2 to SO42- averaged at 3.9 ± 1.6‰. The higher α34Sg→p values in the winter were mainly attributed to the decrease of ambient temperature. We further compared the quantified source apportionments of sulfate by isotope techniques with and without the consideration of fractionation factors. The result revealed that the partitioned emission sources to sulfate with the consideration of the fractionation effects were more logical, highlighting that fractionation effects should be considered in partitioning emission sources to sulfate using sulfur isotope techniques. With considering the fractionation effects, coal burning was the dominant source to sulfate (85.5%), followed by traffic emissions (12.8%) and oil combustion (1.7%). However, the coal combustion for residential heating contributed only 0.9% to sulfate on an annual basis in this megacity.