PubAg

Main content area

Seasonal variability in aerosol optical and physical characteristics estimated using the application of the Ångström formula over Mohal in the northwestern Himalaya, India

Author:
GULERIA, RAJ PAUL, KUNIYAL, JAGDISH CHANDRA, SHARMA, NAND LAL, DHYANI, PITAMBER PRASAD
Source:
Journal of earth system science 2012 v.121 no.3 pp. 697-710
ISSN:
0253-4126
Subject:
winter, Earth system science, monsoon season, aerosols, seasonal variation, wavelengths, India, Himalayan region
Abstract:
Investigations of aerosol optical and physical characteristics using the application of Ångström formula and second order polynomial fit were carried out from April 2006 to March 2009 at Mohal in the Kullu valley. The measurements of spectral aerosol optical depths (AODs) were conducted using multi-wavelength radiometer (MWR). The AOD at 0.5 μm wavelength on daily basis (mean ± standard deviation) for the entire three-year study period is obtained as 0.24 ± 0.08. Seasonal variations show the highest AOD at 0.5 μm wavelength with ~0.34 ± 0.08 during pre-monsoon (April–July), followed by ~0.26 ± 0.08 during monsoon (August–September), ~0.21 ± 0.05 during post-monsoon (October–November) and ~0.20 ± 0.07 during winter (December–March). The seasonal values indicate that the AOD at 0.5 μm wavelength is decreasing from pre-monsoon to winter with a notable reduction around 41%. The Ångström parameters using least square method is not found appropriate for size distribution particularly when coarse mode aerosols dominate. The coefficients of second order polynomial fit are more appropriate for the discrimination of aerosol size or irrespective to the dominance of either of the aerosols size. The difference in coefficient of polynomial fit is used to get confirmation on the dominant mode during different seasons. Study reveals that about 93%, 72% and 59% of AOD spectra are dominated by a wide range of fine mode fractions or mixture of modes during post-monsoon, winter and monsoon, respectively. On the other hand, during pre-monsoon, 72% of AOD spectra are found to be dominated by coarse mode aerosols.
Agid:
195490