Abstract:
Light scattering and absorption properties of at-
mospheric aerosols are of vital importance for evaluating
their types, sources and radiative forcing. This is of partic-
ular interest over the Gangetic–Himalayan (GH) region due
to uplift of aerosol from the plains to the Himalayan range,
causing serious effects on atmospheric heating, glaciology
and monsoon circulation. In this respect, the Ganges Val-
ley Aerosol Experiment (GVAX) was initiated in Nainital
from June 2011 to March 2012 with the aim of examining
the aerosol properties, source regions, uplift mechanisms and
aerosol–radiation–cloud interactions. The present study ex-
amines the temporal (diurnal, monthly, seasonal) evolution
of scattering (σsp ) and absorption (σap ) coefficients, their
wavelength dependence, and the role of the Indo-Gangetic
plains (IGP), boundary-layer dynamics (BLD) and long-
range transport (LRT) in aerosol evolution via the Atmo-
spheric Radiation Measurement Mobile Facility. The anal-
ysis is separated for particles < 10 μm and < 1 μm in diame-
ter in order to examine the influence of particle size on op-
tical properties. The σsp and σap exhibit a pronounced sea-
sonal variation between the monsoon low and post-monsoon
(November) high, while the scattering wavelength expo-
nent exhibits higher values during the monsoon, in contrast
to the absorption Ångström exponent which maximizes in
December–March. The elevated-background measuring site
provides the advantage of examining the LRT of natural and
anthropogenic aerosols from the IGP and southwest Asia and the role of BLD in the aerosol lifting processes. The results
reveal higher aerosol concentrations at noontime along with
an increase in mixing height, suggesting influence from IGP.
The locally emitted aerosols present higher wavelength de-
pendence of the absorption in October–March compared to
the rather well-mixed and aged transported aerosols. Mon-
soon rainfall and seasonally changing air masses contribute
to the alteration of the extensive and intensive aerosol prop-
erties.
