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

Abstract

Investigations of aerosol optical and physical characteristics using the application ofÅngström 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 multiwavelength 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%. TheÅngström 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.

Aerosol climatology at Delhi in the western Indo‐Gangetic Plain: Microphysics, long‐term trends, and source strengths

“…[14] In the present study, values of AODs remained much higher throughout the year, particularly when it is compared with the average AOD values observed at high-altitude Indian stations such as Leh and Hanle , Nainital [Sagar et al, 2004;Ram et al, 2010], Kullu [Guleria et al, 2012], and with the oceanic regions such as Arabian Sea [Satheesh et al, 2006a] and Bay of Bengal [Moorthy et al, 2003;Satheesh et al, 2006b;Beegum et al, 2012]. The AOD at Delhi is slightly higher compared to AODs at some of the other Indian stations like Ahmedabad [Ganguly et al, 2006], Pune [Pandithurai et al, 2007;Dani et al, 2012], Visakhapatnam [Niranjan et al, 2011], Bangalore [Babu et al, 2002;Vinoj et al, 2004], and Trivandrum [Moorthy et al, 2007], but quite comparable with the values at the IGP stations such as Kanpur , Kharagpur [Niranjan et al, 2006], and Bhubneshwar [Das et al, 2009].…”

Aerosols optical depth and Ångström exponent over different regions in Garhwal Himalaya, India

“…Observations on the vertical profile of aerosol and their transport at high altitude regions have also been made by Solanki et al ( 2013 ), Kumar et al ( 2018a , b ); however, more intensive measurements are still needed over the Himalayas which is nearly a data-void region. The Indian Himalaya is topographically very fragile and ecologically very delicate, and further due to the variety of the ecosystem, surface conditions and aerosol properties, in situ observations of aerosols in this part of the Himalayas are therefore very important (Guleria et al, 2011 , 2012 ). Our study mainly focuses on the aerosol variability at various scales, utilizing AOD and AE over a higher-altitude region i.e.…”

Global and regional evaluation of a global model simulated AODs with AERONET and MODIS observations

“…The most common atmospheric processes are turbulent mixing, evaporation, convection, and atmospheric transport (Derimian et al, 2006;Ramachandran and Cherian, 2008;Guleria et al, 2011aGuleria et al, , 2011bVinoj et al, 2014). This result leads to large variations in their size distribution (Kedia and Ramachandran, 2009;Guleria et al, 2012). On the basis of their source strength they are classified as fine mode (r < 0.1 m), accumulation mode (0.1 m ≤ r < 1.0 m) and coarse mode (r ≥ 1.0 m) (Junge, 1963).…”