Aerosol hygroscopicity and photodegradation in the polluted Indo-Gangetic Plain compared with the clean Himalayas examined using a quartz crystal microbalance

Reducing climate uncertainty requires a better understanding of the influence of aerosols on clouds and precipitation, particularly their hygroscopicity under subsaturated conditions, which affects their water uptake, associated optical properties, and radiative impacts. To investigate this, PM
2.5
aerosol samples were analyzed from two contrasting locations: Leh, a high-altitude clean desert plateau in the Himalayas, and Delhi, a heavily polluted urban megacity in the Indo-Gangetic Plain (IGP). A quartz crystal microbalance was used to evaluate hygroscopic growth, including mass loss induced by ultraviolet irradiation. The findings show that Himalayan aerosols have a distinct deliquescence phase transition and high hygroscopicity. In contrast, IGP aerosols have delayed or absent deliquescence and low hygroscopicity. These differences highlight the significant role of chemical composition, particularly the organic fraction, in aerosol behavior. Furthermore, the greater photolytic mass loss observed in Himalayan aerosols suggests the presence of more photolabile components. These results underscore the importance of relative humidity history, chemical composition, and photochemistry in aerosol properties, which are crucial for developing accurate atmospheric models.