Characterization and Impacts of Pre-Monsoonal Dust Events on Aerosol Optical Properties and Snow Albedo in the Indian Himalayas

Dust storms are significant atmospheric events that play a crucial role in altering the regional and global climate system. In this study, we investigate the characteristics and impacts of pre-monsoonal dust loading events over the Indian Himalayas using a combination of satellite observations and in situ aerosol measurements conducted at Mukteshwar, a representative high-altitude site. Ten prominent dust events were identified through satellite-derived aerosol optical depth (AOD) and corroborated with ground-based observations. These events were further classified into two categories based on air mass back-trajectory analysis: Mineral Dust Events (MDEs) and Polluted Dust Events (PDEs). MDEs are characterized by long-range transported dust plumes, primarily from arid regions such as the Thar Desert and the Middle East, traversing the lower troposphere before reaching the Himalayas. Conversely, PDEs are linked to short-range transported dust plumes that originate from the arid western Indian subcontinent but travel through the highly polluted Indo-Gangetic Plain (IGP) boundary layer before reaching the Himalayan foothills.

The study reveals substantial enhancements in aerosol loading and optical properties during these dust events. During both MDEs and PDEs, the mass concentration of coarse particles (2.5-10 µm) increased by approximately 400% (from 24±15 µg/m³ to 98±40 µg/m³), while the extinction coefficient increased by 175% (from 89±57 Mm⁻¹ to 156±79 Mm⁻¹) compared to background conditions. However, there were significant differences in aerosol optical properties between MDEs and PDEs. Single Scattering Albedo (SSA) and Absorption Ångström Exponent (AAE) showed contrasting trends: SSA and AAE increased during MDEs, indicating dominance of mineral dust particles with relatively low light absorption properties, while they decreased during PDEs, highlighting a more substantial contribution from light-absorbing aerosols such as black carbon (BC).

Notably, black carbon concentrations and aerosol absorption coefficients exhibited a twofold increase during PDEs compared to background levels, whereas minimal changes were observed during MDEs. These contrasting aerosol characteristics critically impact snow albedo reduction (SAR) over the Himalayas. SAR during PDEs was nearly double that of background conditions, driven primarily by the enhanced absorption of solar radiation by black carbon and other light-absorbing aerosols. Although SAR also increased during MDEs, the magnitude of change was comparatively lower.

Our findings highlight the dual nature of dust storms impacting the Indian Himalayas: long-range transported MDEs dominated by mineral dust and short-range transported PDEs enriched with black carbon and anthropogenic pollutants. Both categories significantly alter the aerosol optical properties and have distinct yet substantial effects on snow albedo and subsequent glacier melting processes. These findings highlight the necessity of thorough modeling and observational research to more accurately estimate the long-term effects of dust-induced snow albedo reduction on the Himalayan region.