Aerosol volatility over High-Altitude site in Western Ghats, India: Effect of semi-volatile organics coating

Sub-micron aerosols are primarily consisted of organics, sulfate, nitrate, ammonium etc. and among which organics have high complexity in its chemical and physical characteristics. In the present study, aerosol volatility of non-refractory sub-micron aerosol was extensively studied during 6^th – 20^th February of 2021 utilizing high-resolution Time of flight Aerosol Mass Spectrometer (HR-TOF AMS) coupled with Thermal denuder. The temperature was set to 150^oC and the denuded and non-denuded ambient aerosol was then sampled utilizing a switching valve with 10 minute time interval. Nitrate and Ammonium possessed highest volatility (80% and 68%) which was followed by organics with volatility rate of 54%. Sulfate was observed to be the least volatile (26%).The volatility extent for organics was low in afternoon and night-early morning hours due to possible prevalence of oxygenated organic aerosols (secondary organic aerosol) during these time period. Further PMF was done on the denuded and non-denuded organics aerosol dataset and the analysis revealed 4 factors namely, Hydrocarbon like organic aerosol (HOA), Biomass burning organic aerosol (BBOA), semi-volatile oxygenated organic aerosol (SVOOA) and low-volatile oxygenated organic aerosol (LV-OOA). LV-OOA fractional contribution increased from 31% to 56% of total organics. SVOOA, HOA, BBOA being a primary aerosol, showed decreasing trend as they have higher volatility than LVOOA. Interestingly, of SV-OOA volatility was even higher than that of the other primary aerosols (HOA, BBOA). The possible reason may be SV-OOA is freshly formed and can be deposited on to pre-existing aerosols like inorganic aerosols, HOA, BBOA, LV-OOA etc which indicated the effect of possible coating.