AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Size-resolved CCN Activity in Winter Season at a Polluted Site, Kanpur in India
DEEPIKA BHATTU, S.N. Tripathi, IIT Kanpur
Abstract Number: 152 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosols can act as cloud condensation nuclei, based on their size and chemical composition, thus indirectly affecting the microphysical properties, lifetime and coverage of clouds (Albrecht, 1989). Past studies suggested that the precise quantification is required when CCN/CN is non-linearly correlated with total aerosol concentration and involves complexity due to ageing processes (Deng et al., 2013). Size-resolved CCN activity studies provide information on the relative influence of chemical composition and aerosol size distribution on CCN prediction, mixing state of aerosols and the processes affecting their hygroscopic growth (Padró et al., 2012). They also help in understanding the origin of hygroscopicity of ambient aerosols by studying the activation kinetics of organic compounds. The information on chemical composition and mixing state should be carefully incorporated in the CCN closure studies specifically where anthropogenic emissions are high.
Size-resolved CCN measurements were conducted in winter, 2012 for particles in the size range from 20 to 280 nanometer for SS=0.2% -1.2%. The chemical composition of organics and inorganics (NH$4$^+, NO$^3$_-, SO$^4$_2-, Cl$^-) was obtained from HR-ToF-AMS using a chemically dependent CE of 0.45. The aim of this study is to characterize the aerosol hygroscopic properties and infer mixing state of aerosols. The accumulation mode (>100 nanometer) particles are more hygroscopic (κ$_CCN=0.24) than Aitken mode (40-100 nanometer) particles (κ$_CCN=0.13). In hygroscopicity closure, κ$_AMS > κ$_CCN at lower diameter due to the presence of refractory aerosols which were not measured by AMS. However, at higher diameter, κ$_CCN > κ$_AMS due to presence of externally mixed organic aerosols which are not CCN active. Higher differences in κ$_AMS and κ$_CCN at higher diameter at night because of the presence of high organic fraction. Further, a transition period is examined for the change in total aerosol properties like, activation diameter, oxidation state, aerosol mixing state and hygroscopicity of aerosols.