Multiple Sulfur Isotope Constraints on Sources and Formation Processes of Sulfate in Beijing PM Aerosol.

Recently air pollution is seriously threatening the health of millions of people in China. The multiple sulfur isotopic composition of sulfate in PM samples collected in Beijing is used to better constrain potential sources and formation processes of sulfate aerosol. The ΔS values of sulfate in PM show a pronounced seasonality with positive values in spring, summer and autumn and negative values in winter. Positive ΔS anomalies are interpreted to result from SO photolysis with self-shielding, and may reflect air mass transport between the troposphere and the stratosphere. The negative ΔS signature (-0.300‰ < ΔS < 0‰) in winter is possibly related to incomplete combustion of coal in residential stoves during the heating season, implying that sulfur dioxide released from residential stoves in more rural areas is an important contributor to atmospheric sulfate. However, negative ΔS anomalies (-0.664‰ < ΔS ← 0.300‰) in winter and positive ΔS anomalies (0.300‰ < ΔS < 0.480‰) in spring, summer, and autumn suggest sulfur isotopic equilibrium on an annual time frame, which may provide an implication for the absence of mass-independent fractionation of sulfur isotopes (S-MIF) in younger sediments. Results obtained here reveal that reducing the usage of coal and improving the heating system in rural areas will be important for efficiently decreasing the emissions of sulfur in China and beyond.