The COVID lockdown presented a unique opportunity to study the anthropogenic emissions from different sectors under relatively cleaner conditions in India. The complex interplays of power production, industry, and transport could be dissected due to the significantly reduced influence of the latter two emission sources. Here, based on measurements of cloud condensation nuclei (CCN) activity and chemical composition of atmospheric aerosols during the lockdown, we report an episodic event showing rapid growth and high hygroscopicity of new aerosol particles formed in the SO2 plume from a large coal-fired power plant. These sulfate-rich particles had high CCN activity and number concentration, indicating high cloud-forming potential. Examining the sensitivity of CCN properties under relatively clean conditions over India provides important new clues to delineate contributions of different anthropogenic emission sectors and further to understand their perturbations of past and future climate forcing.
