Direct Observation of Sulfate Explosive Growth in Wet Plumes Emitted From Typical Coal-Fired Stationary Sources

The origins of atmospheric sulfate production have previously been explained by focusing on air quality models and complex chemical reaction processes. Here, we first report direct observations of sulfate production in stack plumes discharged from coal-fired power plants, industrial boilers, and sintering plants equipped with wet desulfurization systems. Less than one third of the particulate SO42- in plumes is attributed to dust-SO42- and SO3 measured in stacks. The SO2 aqueous-phase oxidation process is critical in explaining the unknown sulfate formation in plume droplets with pH values ranging from 2.3 to 2.8. When the rapidly formed sulfate in wet plumes is included, a notable amount of underestimated sulfate (similar to 0.24 Tg in 2017) is emitted from industrial stacks in China and can partially explain the missing sulfate on driving most particle pollution episodes. Policy-making targeting particulate emissions is suggested to substantially reduce sulfate emissions for further air quality improvement.

Automated summary

Observations showed that sulfate production in stack plumes equipped with wet desulfurization systems was previously underestimated, partially explaining the missing sulfate in most particle pollution episodes. Policymakers are suggested to target particulate emissions in order to reduce sulfate emissions for further air quality improvement.