Volatility of secondary organic aerosol from the ozonolysis of monoterpenes

Abstract

The volatility of secondary organic aerosol (SOA) produced from the ozonolysis of α-pinene, β-pinene, and limonene, at low and intermediate RH, and at low and high NOx conditions was investigated using a thermodenuder (TD). More than 90% of the α-pinene and β-pinene SOA volume (for 200nm particles) and approximately 75% of the limonene SOA evaporated at 70°C for a centerline residence time of approximately 16s in the heated zone. Practically all the SOA in all systems evaporated at approximately 90°C. The relative humidity during the formation of SOA had a small effect on its volatility (changes in the evaporated fraction were less than 10%). NOx concentrations had a significant impact on the volatility of α-pinene and β-pinene SOA (reductions of the evaporated fraction by approximately 30%), but a negligible effect on the volatility of limonene SOA. High NOx levels resulted in more volatile SOA than low NOx conditions due to the presence of relatively volatile nitrate containing species at high NOx.The behavior of the SOA in the thermodenuder can be reproduced using an aerosol dynamics model based on the volatility basis-set approach and SOA yield parameters derived in previous smog chamber studies if appropriate values of the mass accommodation coefficient and heat of vaporization (ΔHvap) are chosen. Use of either a very low effective accommodation coefficient (0.002-0.01) and a heat of vaporization depending on the saturation concentration, or an effective accommodation coefficient of 0.05 for the initial stages of the evaporation and 1 afterward, with a low volatility-independent value of the ΔHvap, is needed for the simulation of the SOA evaporation. © 2011 Elsevier Ltd.