2:15 PM - 2:30 PM
[AAS07-13] Enhancement of the secondary organic aerosol yields and the formation of low- and extremely low-volatility organic compounds during the oxidations of α-pinene in the presence of acidic seeds
Keywords:α-Pinene, Photooxidation, Ozonolysis, Secondary organic aerosol, SOA yield, Organosulfate
Secondary organic aerosols (SOAs) affect human health and climate change; however, the factors (e.g., temperature, acidity of pre-existing particles, and oxidants) influencing their formation are not sufficiently understood. The temperature and acidity dependence of SOA yields and chemical components of SOA from α-pinene ozonolysis and α-pinene photooxidation under low NOx conditions were systematically investigated under 278–298 K temperatures in the presence of neutral ((NH4)2SO4) and acidic (H2SO4 + ((NH4)2SO4)) seeds by using a compact chamber. The slight negative temperature dependence of the SOA yields was observed and the enthalpies of vaporization were estimated to be 25–48 kJ mo–1, which is in agreement with the value of 40 kJ mol–1 applied in the CMAQ model. The SOA yields increased ~10–30 % with the increase in the acidity of seed particles ([H+] = 220 nmol m–3) at low SOA mass loadings. Those increases were thought to be caused by the formation of low- and extremely low-volatility organic compounds such as dimer esters and organosulfates, which were measured by means of negative electrospray ionization liquid-chromatography time-of-flight mass spectrometry coupled to ion mobility spectrometry. To achieve better simulation of monoterpene SOA formation in the SOA module of the model, we propose that the conversion rate (τ–1) of semi-volatile organic compounds (SVOCs) to non-volatile compounds (NVOCs) should be faster under acidic conditions compared with that under neutral conditions.