Seasonal inhomogeneity in cloud precursors over Gangetic Himalayan region during GVAX campaign

Atmospheric aerosols are key elements in cloud microphysics, the hydrological cycle and climate by serving as cloud condensation nuclei (CCN). The present work analyzes simultaneous measurements of number concentration of CCN (N-CCN) and condensation nuclei (N-CN) obtained at Nainital, in the Gangetic-Himalayan (GH) region, during the frameworks of Ganges Valley Aerosol Experiment (GVAX), June 2011 to March 2012. The N-CCN, N-CN and activation (AR = N-CCN/N-CN) at 031-033% S (supersaturation ratio), exhibit significant daily, monthly and seasonal variations within a range of 684-2065 cm(-3) for N-CCN 1606-4124 cm(-3) for N-CN, and 038-0.60 for AR, suggesting large inhomogeneity in aerosol properties, types and sources, which control the degree of aerosol potential activation. Thus, transported aerosols from the Ganges valley and abroad, the boundary-layer dynamics and atmospheric modification processes play an important role in aerosol-cloud interactions over the GH region. The N-CN and N-CCN show monthly-dependent diurnal variations with afternoon maxima due to transported aerosols from the Ganges valley up to the Himalayan foothills, while the AR is lower during these hours implying lower hygroscopicities or smaller sizes of the transported aerosols. The dependence of N-CCN on S is highest during Dec-Mar and lowest during monsoon (Jun-Sep), suggesting different aerosol chemical composition. Comparison between Nainital and Kanpur shows that N-CN and N-CCN are much lower at Nainital, while the similarity in AR suggests aerosols of similar type, source and chemical composition uplifted from the Ganges valley to the Himalayan foothills. (C) 2014 Elsevier B.V. All rights reserved.