Characterization of aerosol optical and radiative properties at Leh, located over the climate sensitive Hindu Kush Himalayan region using sky radiometer observation

Abstract

Aerosol optical and radiative properties over the Leh Ladakh, located in the climate sensitive Hindu Kush Himalayan region are examined using one year measurements from a newly installed sky radiometer from July 2023 to June 2024. Columnar aerosol optical depth (AOD), at 500 nm exhibits a distinct seasonal variation with peak during spring (0.104 ± 0.041) and minimum in autumn (0.077 ± 0.031), while Extinction Angstrom Exponent (EAE) is found to be maximum in winter (1.041 ± 0.205) and minimum (0.658 ± 0.225) in spring. The highest EAE in winter is complemented with the highest AOD_Fine-mode (0.071 ± 0.034) among the seasons which may be associated with the combustion of firewood, charcoal, kerosene or other fuels used to burn to bear the cold winter months, when temperature varied between −15 and −25 ◦C. Seasonal variation of Single Scattering Albedo (SSA) at 500 nm varied from 0.905 ± 0.055 (winter) to 0.942 ± 0.061 (summer), while the lowest value of SSA during winter is complemented with more absorbing aerosols during winter season. The dominance of fine mode aerosols during the winter seasons is also complemented by the bi-modal volume size distribution. However, the station is experiencing a negligible contribution of dust-aerosols (1%), followed by 18% mixed aerosols and 16% non-absorbing aerosols. The current observing site is dominated by absorbing aerosols which contributed by highly absorbing (49%), moderately absorbing (9%) and slightly absorbing (6%) during the one year of study period. The absorbing aerosols are characterized by high values of AOD_Fine-mode (0.061 ± 0.028), imaginary refractive-index (0.014 ± 0.009), EAE (0.932 ± 0.240) and low value of SSA_Total (0.872 ± 0.070). On the other hand, the non-absorbing aerosols are characterized by high values of AOD_Total (0.088 ± 0.040), SSA_Total (0.991 ± 0.016), SSA_Coarse-mode (0.978 ± 0.038), and low value of imaginary refractive-index (∼0.001). The estimated aerosol radiative forcing (ARF) reveals the high heating rates during spring (0.09 K day−1) among the seasons, while the heating rate is found to be highest by absorbing aerosols (0.08 K day−1) among the aerosol types.