First surface measurement of cloud condensation nuclei over Kanpur, IGP: Role of long range transport

Abstract

Measurements have been carried out for cloud condensation nuclei (N CCN, number concentration at 0.38% average depleted supersaturation, SS) and submicron aerosol (N CN), using a CCN (cloud condensation nuclei) counter (Droplet Measurement Technology) and Scanning Mobility Particle Sizer (TSI), respectively, for a large number of days in each season of the year 2008 and 2009 at Kanpur, North India. Aerosol chemical composition was also measured for 3 days and 3 nights during November-December 2009. N CCN was generally much higher than observed at similar environments elsewhere except in Chinese cities. Due to higher loading of CCN the supersaturation depletion correction is applied. Significant intraseasonal variability was observed in N CCNand CCN/CN ratio (N CCN/N CN), due to different air masses coming from north-west, east, and central parts of India. The CCN concentrations at 0.38% and CCN/CN ratio for the year 2008 varied between 10,043-12,107 cm -3 and 0.12-0.30 in winter season and 5942-7184 cm -3 and 0.07-0.15 in premonsoon season, respectively. For 2009, it varied between 10,518-13,029 cm -3 and 0.28-0.53 in winter season and 3596-8040 cm -3 and 0.20-0.28 in postmonsoon season, respectively. Higher CCN/CN ratio was observed during winter season when the air mass came from north-west, central, and eastern landmass of India. This was most likely due to relatively high accumulation mode particle concentration and large number of forest fires observed in those regions. As expected, polluted continental air masses lead to a significant increase in CCN concentrations over the winter months, most likely due to increased anthropogenic activities, i.e., increased fuel usage, large biomass burning coupled with lower mixed boundary layers. A closure study was performed by application of Köhler theory, utilizing chemical composition, and size distribution measured by SMPS. CCN concentrations were predicted for 3 days and 3 nights and these values were compared with measured CCN values at 0.13, 0.33, and 0.64% SS. In the present closure study, CCN values were slightly overpredicted to the extent of 21% ± 18%. Copyright © American Association for Aerosol Research.