Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory-Pyramid (5079 m a.s.l.) 1Institute of Atmospheric Sciences and Climate CNR, Rome, Italy
2Institute of Atmospheric Sciences and Climate CNR, Bologna, Italy
3Ev-K2-CNR Organization, Bergamo, Italy
Received: 03 Dec 2009 – Published in Atmos. Chem. Phys. Discuss.: 18 Jan 2010 Abstract. In spite of being located at the heart of the highest mountain range in the
world, the Himalayan Nepal Climate Observatory (5079 m a.s.l.) at the Ev-K2-CNR
Pyramid is shown to be affected by the advection of pollution aerosols from
the populated regions of southern Nepal and the Indo-Gangetic plains. Such
an impact is observed along most of the period April 2006–March 2007
addressed here, with a minimum in the monsoon season.
Backtrajectory-analysis indicates long-range transport episodes occurring in
this year to originate mainly in the west Asian deserts. At this high
altitude site, the measured aerosol optical depth is observed to be about
one order of magnitude lower than the one measured at Ghandi College (60 m a.s.l.),
in the Indo-Gangetic basin. As for Ghandi College, and in agreement
with the in situ ground observations at the Pyramid, the fine mode aerosol
optical depth maximizes during winter and minimizes in the monsoon season.
Conversely, total optical depth maximizes during the monsoon due to the
occurrence of elevated, coarse particle layers. Possible origins of these
particles are wind erosion from the surrounding peaks and hydrated/cloud-processed aerosols.
Assessment of the aerosol radiative forcing is then expected to be hampered
by the presence of these high altitude particle layers, which impede an
effective, continuous measurement of anthropogenic aerosol radiative
properties from sky radiance inversions and/or ground measurements alone.
Even though the retrieved absorption coefficients of pollution aerosols were
rather large (single scattering albedo of the order of 0.6–0.9 were observed
in the month of April 2006), the corresponding low optical depths (~0.03
at 500 nm) are expected to limit the relevant radiative forcing.
Still, the high specific forcing of this aerosol and its capability of
altering snow surface albedo provide good reasons for continuous monitoring.
Revised: 01 Oct 2010 – Accepted: 17 Nov 2010 – Published: 29 Nov 2010
Citation: Gobbi, G. P., Angelini, F., Bonasoni, P., Verza, G. P., Marinoni, A., and Barnaba, F.: Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory-Pyramid (5079 m a.s.l.), Atmos. Chem. Phys., 10, 11209-11221, doi:10.5194/acp-10-11209-2010, 2010.