Exploring the Influence of 34S Fractionation From Emission Sources and SO2 Atmospheric Oxidation on Sulfate Source Apportionment Based on Hourly Resolution δ34S‐SO2/SO42−.

Sulfate (SO42−) sources are unclear leading to the underestimation of its concentration in the model. Hourly resolution δ34S‐SO2 and δ34S‐SO42− values of three haze episodes (EP1‐EP3) were synchronously collected for the first time to quantify the influence of 34S fractionation from emission sources (e.g., coal combustion) and SO2 atmospheric oxidation on SO2/SO42− source apportionment. After considering the 34S fractionation from coal combustion and atmospheric oxidation, the reasonable and logical source contributions of SO42− were obtained, showing highly consistent with that of Positive Matrix Factorization model results. Considering the 34S fraction from atmospheric oxidation, the source apportionment of SO2/SO42− obtained by hourly resolution δ34S‐SO2 and δ34S‐SO42− can more accurately reflect the dynamic changes of emission sources. Traffic emissions (49%) and coal combustion (46%–65%) were the major contributors to SO2/SO42− in EP1 and EP2‐EP3, respectively. However, obvious deviations of coal combustion contribution were found without considering 34S fractionation from coal combustion. Especially for the northwest transmission channels in EP2‐EP3, the deviation values accounted for 17.1%–38.5% of secondary SO42−. Moreover, δ34S was considered as a more sensitive source indicator than SO2 concentration by the results comparison of 34S technique and air quality model (Nested Air Quality Prediction Model System), which can provide more reliable evidence for SO2 emission control. Plain Language Summary: Inadequate understanding of sulfate (SO42−) sources leads to the deviation of its concentration prediction in the model. Based on the hourly resolution δ34S values of SO2 and SO42− during three haze episodes, this study investigated the influence of 34S fractionation from emission sources and the SO2 oxidation process on the source contributions of SO42−. We found that the source contributions of SO42− were more reasonable when considered the 34S fractionation from coal combustion and SO2 atmospheric oxidation, which were similar to the results of Positive Matrix Factorization model. Considering the 34S fractionation from SO2 oxidation process, we also obtained the dynamic source contributions of SO42− in haze episodes, showing traffic emission (49%) and coal combustion (46%–65%) as the major contributors to SO42− in EP1 and EP2‐EP3, respectively. Otherwise, ignoring the 34S fractionation from coal combustion, the contribution of coal combustion to SO42− showed great deviations (17.1%–38.5% of secondary SO42−). Finally, the result comparisons of SO42− sources between 34S and air quality model showed 34S as a more sensitive source indicator than SO2 concentration to trace the source emission and make emission reduction measures in the future. Key Points: Reasonable and logical source contributions of SO42− were obtained with considering the 34S fractionation effects from coal combustion and atmospheric oxidation processesEvidence from 34S showed that traffic emission and coal combustion were major contributors to SO42− in EP1 and EP2‐EP3, respectivelyCompared with SO2 concentration, 34S is a more sensitive index to trace the SO2/SO42− emission sources in the future [ABSTRACT FROM AUTHOR]