Dr. Deepika Bhattu, Scientist, Paul Scherrer Institute (PSI), Villigen, Switzerland
Aerosols can indirectly affect the cloud formation and associated properties by acting as cloud condensation nuclei (CCN), and serve as one of the largest sources of uncertainty in understanding the present-day climate sensitivity (Intergovernmental Panel on Climate Change, 2013). Several CCN studies have been done globally to constrain the uncertain aspects of aerosol-cloud interactions. However, the dependence on source, type and distance of aerosols, and meteorological conditions restricts generalization of such properties over global scale. So far, a handful of studies have investigated the average effect of bulk chemical composition on CCN potential in different seasons but a comprehensive investigation of the other underlying parameters is lacking. This talk outlines a better understanding of the CCN activation potential of ambient aerosols based on size, chemical composition, mixing state, and thermodynamic properties. It describes the deconvoluted effect of size and chemical composition on CCN prediction in an anthropogenically polluted environment. How the solubility and mixing state of aerosols affect the CCN prediction? How to infer the mixing state in the absence of single particle measurement techniques? Impact of volatility on aerosol hygroscopicity and CCN prediction will also be discussed. As per our knowledge, this is the first study of its own kind in whole Indian sub-continent providing detailed information on CCN population that can act as a framework to establish empirical hygroscopicity relationships for climate models. These derived parameterizations can be used to relate aerosol properties to cloud formation and precipitation levels. The second part of my talk focuses on the comprehensive understanding of the sources of carbonaceous aerosols in the ambient atmosphere. It combines both laboratory experiments deploying different combustion sources e.g., wood combustion devices and test vehicles, and ambient study. A complete assessment of primary gas and particle phase emissions and their secondary organic aerosol (SOA) formation potential from different technologies and their operating conditions and mitigation measures, if any, will be discussed. Further, I will present the chemical characterization and source apportionment of PM2.5 aerosols in a polluted megacity, New Delhi, using an advanced mass spectrometry.