Elucidating the Complexity of Mass-Based Hygroscopicity and Photochemical Transformation of Himalayan Aerosols as Revealed by Piezoelectric Technique
SHAILINA SRIVASTAVA, Aishwarya Singh, Tariq Ahmed, Amar Krishna Gopinath, Bin Bai, Christi Jose, Rizana Salim, Subrat Sharma, R. Ravikrishna, Pengfei Liu, Sachin S. Gunthe, Indian Institute of Technology Madras, India
Abstract Number: 633
Working Group: Aerosols, Clouds and Climate
Abstract
Atmospheric aerosols are key players in Earth’s climate system, originating from both direct emissions and secondary formation through chemical reactions of gaseous precursors. Their climatic effects include directly scattering or absorbing solar radiation and indirect effects by acting as cloud condensation nuclei (CCN) or ice nuclei (IN), thereby perturbing cloud formation and precipitation. To better understand the role aerosol play in cloud and precipitation formation is crucial for reducing the climate uncertainty. One such critical aspect is to assess their hygroscopicity in sub-saturated region as knowing RH dependent history of aerosol particles is critical for improved understanding of water uptake, phase states, viscosity, and radiative impact of atmospheric aerosols. Additionally, investigating the seldom-studied transformation process of photodegradation is vital for gaining insights into the atmospheric evolution and lifespan of aerosol particles. Aerosol samples (PM2.5 and PM10) were collected from Ladakh, a climatically and geographically unique high-altitude cold desert plateau (~3400 m a.s.l.) located in the Indian Himalayan ranges. PM2.5 particles were transferred as a thin film on QCM (Quartz Crystal Microbalance) sensors and subjected to RH variations (1–90%) to evaluate hygroscopic growth. Key parameters including, mass-based hygroscopic growth factor (gfm), hygroscopicity parameter (κm), deliquescence relative humidity (DRH), and UV-induced mass loss, were analyzed. The κm values ranged from 0.04 to 0.06, with DRH between 65–78%, indicating a mixture of organic and inorganic species. The relatively low κm and high DRH values suggest the dominance of water-insoluble organics with limited hygroscopic potential. Photodegradation under UV exposure resulted in an average mass loss of 9.16%, implying the presence of low-volatility oxygenated organics. Complementary comprehensive chemical characterization included ion chromatography for water-soluble ions, ICP-MS for elemental profiling, OC/EC analysis, and scanning electron microscopy imaging. Further detailed findings will be presented.