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Abstract:
The contribution of atmospheric aerosols in perturbing cloud formation and precipitation is highly reliant on their microphysical and chemical properties. To understand the implications of anthropogenic emissions on cloud formation under relatively clean conditions during the Covid lockdown, we performed detailed measurements of the cloud-forming potential and chemical properties of ambient aerosols in Chennai, India. Our observations of aerosol composition, growth rate, CCN number concentration, and hygroscopicity revealed a unique event of new particle formation and rapid growth in the SO2 plume of a large coal-fired power plant reaching the tropical coastal environment of the measurement site. Unlike the majority of previously reported NPF events, which are triggered by organic precursors, this event was induced by high sulfate concentrations. Apparently, condensation of H2SO4 from oxidation of the SO2 plume arising from the Neyveli power plant, located about 200 km south of the observation site, elevated sulfate levels, resulting in rapid particle formation and growth. Under the business-as-usual scenario, such new particle formation and growth would be suppressed due to the sizeable aerosol surface area already present from local sources of H2SO4 condensation and particle coagulation. The observed sulfate-rich particles exhibited unusually high CCN activity and number concentration over a varying range of supersaturations with κ values higher than the business-as-usual scenario, indicating high cloud formation potential. To our knowledge, our results are the first direct observations demonstrating that SO2 emissions from coal-fired power plants strongly enhance the CCN activity of aerosol particles. In addition, this study also emphasizes the importance of increased aerosol mass loading due to the formation of new particles, which must be carefully considered while designing strategies to mitigate PM2.5 pollution in coastal areas across India.
