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

Abstract Sulfate (SO 4 2− ) sources are unclear leading to the underestimation of its concentration in the model. Hourly resolution δ 34 S‐SO 2 and δ 34 S‐SO 4 2− values of three haze episodes (EP1‐EP3) were synchronously collected for the first time to quantify the influence of 34 S fractionation from emission sources (e.g., coal combustion) and SO 2 atmospheric oxidation on SO 2 /SO 4 2− source apportionment. After considering the 34 S fractionation from coal combustion and atmospheric oxidation, the reasonable and logical source contributions of SO 4 2− were obtained, showing highly consistent with that of Positive Matrix Factorization model results. Considering the 34 S fraction from atmospheric oxidation, the source apportionment of SO 2 /SO 4 2− obtained by hourly resolution δ 34 S‐SO 2 and δ 34 S‐SO 4 2− can more accurately reflect the dynamic changes of emission sources. Traffic emissions (49%) and coal combustion (46%–65%) were the major contributors to SO 2 /SO 4 2− in EP1 and EP2‐EP3, respectively. However, obvious deviations of coal combustion contribution were found without considering 34 S fractionation from coal combustion. Especially for the northwest transmission channels in EP2‐EP3, the deviation values accounted for 17.1%–38.5% of secondary SO 4 2− . Moreover, δ 34 S was considered as a more sensitive source indicator than SO 2 concentration by the results comparison of 34 S technique and air quality model (Nested Air Quality Prediction Model System), which can provide more reliable evidence for SO 2 emission control.