Rapid growth and high cloud-forming potential of anthropogenic sulfate aerosol in a thermal power plant plume during COVID lockdown in India

The COVID lockdown presented an interesting 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 resulting from distinct meteorological conditions. This event was marked by rapid growth and high hygroscopicity of new aerosol particles formed in the SO2 plume from a large coal-fired power plant in Southern India. 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 provides important new clues to delineate the contributions of different anthropogenic emission sectors and further to understand their perturbations of past and future climate forcing

Chemical Characterization and Source Apportionment of Organic Aerosols in the Coastal City of Chennai, India: Impact of Marine Air Masses on Aerosol Chemical Composition and Potential for Secondary Organic Aerosol Formation

Online chemical characterization of NR-PM1 (nonrefractory particulate matter ≤1 μm) has been carried out using an ACSM (Aerosol Chemical Speciation Monitor) at a coastal urban site in Chennai, India. The average mass concentration of NR-PM1 during the campaign was 30.4 ± 28.3 μg/m3 (arithmetic mean ± standard deviation) with organics accounting for a major fraction of ∼47.4% followed by sulfate (∼33.3%). Back trajectory analysis and STILT model simulations enabled the identification of a relatively clean period with prevailing air masses from ocean. During this period, the average NR-PM1 mass concentration was 7.1 ± 2.8 μg/m3, which is ∼5 times lower than that of the rest of the campaign (with air masses sampled from both continent and ocean) (33.3 ± 29.1 μg/m3). This reduction was primarily attributed to the dilution of local primary emissions due to cleaner marine influx. Comprehensive source apportionment for the organic fraction was performed using Positive Matrix Factorization (PMF). While equal contributions of primary (∼49%) and secondary (∼51%) organic factors were observed for the rest of the campaign, more oxidized-oxygenated organic aerosol (MO-OOA) factor dominated the OA and accounted for ∼82% of the total OA mass during the clean period. Simultaneously, during the clean period a significant increase in the fraction of organic liquid water was observed. We studied the effect of marine influx on the enhanced secondary organic aerosol (SOA) fraction. In brief, our results demonstrate the significance of marine winds and meteorological conditions on the chemical composition and ambient aerosol mass burden at a coastal site. Further, this study emphasizes that marine influx can cause the dilution in local pollution and can demonstrate distinct chemical composition with impacts on local aerosol properties