Abstract
Extensive measurements of spectral aerosol optical depths (AODs) were made at Manora Peak, Nainital (29.4°N, 79.5°E,~1958 m above mean sea level) in the central Himalayas, using a ten channel multi-wavelength solar radiometer during January 2002 to December 2005. Using these spectral AOD values, the columnar size distribution [CSD; n(subscript c)(r)] function of aerosols have been derived. The CSD, retrieved from spectral AODs are, in general, bimodal (combination of power law and unimodal log normal distribution) with a prominent secondary (or coarse) mode occurring at a fairly large value of radius (r＞0.5 μm), while the primary (or fine) mode either does not appear explicitly or perhaps occurs below the radius ≌0.1 μm. The bimodal nature of CSDs indicates the presence of fine as well as coarse mode aerosols over the observational site. The effective radius, total aerosol number content and columnar mass loading computed from deduced CSD shows minimum values during winter (November to February) and maximum during summer (March to June) months. The share of sub micron and super micron aerosols to the total aerosol number concentration (N(subscript t)) indicates the dominance of sub micron aerosols to the N(subscript t) and it accounts for ＞90% during the study period.
Highlights
Size distribution is one of the most prominent properties of atmospheric aerosols from the stand point of climate impact
In the present investigation we present the columnar size distribution (CSD) function inferred by numerical inversion of spectral aerosol optical depth (AOD) measurements over a period of four years (January 2002 to December 2005)
The typical CSD obtained for December 2004 (Fig. 2) has two panels, the lower panel (b) representing the retrieved CSDs in a log-log scale, while the upper panel (a) depicts the measured AODs along with the reestimated AODs from the retrieved CSDs as shown in panel (b)
Summary
Size distribution is one of the most prominent properties of atmospheric aerosols from the stand point of climate impact.
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