Diurnal features of aerosol optical depth (AOD) at a high-altitude station, Hanle (4500 m amsl) in the western Himalayas, were studied using direct/diffuse solar irradiance measurement from a Sky-radiometer (Prede) during October 2007 to December 2010. The study reveals a diurnal asymmetry in the measured aerosol characteristics, with three types of diurnal variation in AOD. Among them, Types I and II are prominent during pre-monsoon, while Type III dominates during post-monsoon. Type I ap-pears to be associated with new-particle formation process from gaseous precursors, in addition to the combination of anthropogenic and desert-dust aerosols, probably brought by the prevailing westerly/ south-westerly winds during the pre-monsoon season. The diurnal feature of the Type II may be at-tributed by the transported desert-dust aerosols brought by the prevailing winds. Further, Type III may be associated with the aged background aerosols over the region, pertaining to a small contribution from gaseous precursors. & Elsevier Ltd. All rights reserved.