Abstract:
The seasonality and mutual dependence of aerosol optical properties and cloud condensation
nuclei (CCN) activity under varying meteorological conditions at the high-altitude Nainital site (~2 km) in
the Indo-Gangetic Plains were examined using nearly year-round measurements (June 2011 to March 2012)
at the Atmospheric Radiation Measurement mobile facility as part of the Regional Aerosol Warming
Experiment–Ganges Valley Aerosol Experiment of the Indian Space Research Organization and the U.S.
Department of Energy. The results from collocated measurements provided enhanced aerosol scattering
and absorption coefficients, CCN concentrations, and total condensation nuclei concentrations during
the dry autumn and wintermonths. The CCN concentration (at a supersaturation of 0.46) was higher during
the periods of high aerosol absorption (single scattering albedo (SSA)<0.80) than during the periods of
high aerosol scattering (SSA>0.85), indicating that the aerosol composition seasonally changes and influences
the CCN activity. The monthly mean CCN activation ratio (at a supersaturation of 0.46) was highest (>0.7)
in late autumn (November); this finding is attributed to the contribution of biomass-burning aerosols to
CCN formation at high supersaturation conditions.
