Aerosol volatility over a high-altitude site in India: Effect of semi-volatile organics

Sub-micron aerosols primarily comprise of organics, sulfate, nitrate, ammonium, and chloride. Of these, organics have high complexity in their chemical and physical characteristics. In this study, aerosol volatility of non-refractory sub-micron aerosol was studied using a thermal denuder (at a constant temperature of 150 °C) coupled High-Resolution Time of flight Aerosol Mass Spectrometer (HR-TOF AMS) for the period from 6th to 26th February 2021. Nitrate and ammonium had the highest volatility (80 % and 68 %, respectively), followed by organics (54 %). The lowest volatility rate was observed for sulfate (26 %) indicating the tendency of sulfate aerosols to be more in the particle phase at higher temperatures. The volatility for organics decreases during afternoon and midnight hours due to the prevalence of secondary organic aerosol. Further positive matrix factorization (PMF) analysis on both the denuded and ambient organics aerosol revealed four factors, namely, hydrocarbon-like organic aerosols (HOA), biomass-burning organic aerosol (BBOA), semi-volatile oxygenated organic aerosol (SV-OOA), and low-volatile oxygenated organic aerosol (LV-OOA). Over the campaign, LV-OOA showed an increase in fractional contribution from 31 % to 56 % of total organics. SV-OOA, HOA, and BBOA showed decreasing trends, as they have higher volatility than LV-OOA. Surprisingly, SV-OOA exhibited higher volatility than that of HOA, and BBOA. Further, the volatility of oxygenated hydrocarbon peaks was compared with hydrocarbon peaks to assess the higher volatility of SV-OOA aerosols, and the oxygenated hydrocarbons were estimated to be more volatile than hydrocarbons. The present study highlighted the possible coating of SV-OOA over the existing aerosols which may modulate the aerosol to cloud condensation nuclei (CCN) activation characteristics. • Sub-micron aerosol volatility was extensively studied at high-altitude site, India. • Sulfate exhibited minimum volatility (26 %) among all the sub-micron constituents. • SV-OOA was highest contributor to total OA in ambient aerosol. • Highest volatility of SV-OOA among all organics components. • The higher volatility of oxygenated hydrocarbon further indicated possible coating.