Volatility of atmospheric organic aerosol

Atmospheric organic aerosols play a significant role in atmospheric chemistry and physics. The volatility of the corresponding compounds determines their partitioning between the gas and particulate phases and can provide indirect information about the OA chemical composition and age. The main objective of this research is to improve our understanding of the volatility of atmospheric organic aerosol by measuring and modeling the evaporation rate of these particles in both the laboratory. A thermodenuder (TD) was developed and improved to allow a wide range of residence times of the aerosol in the heated zone. The performance of the thermodenuder was first tested using a nearly monodisperse single-component aerosol. The measured volatility of these model particles was consistent with their vapor pressure. An aerosol dynamic model was developed in order to provide a general method to interpret the TD volatility measurements. The model simulates the time-dependent evaporation of particles inside the thermodenuder by solving the corresponding mass transfer equations in the transition regime. The model was tested with the single-component aerosol whose thermodynamic properties are well known.;The volatility of ambient aged organic aerosol was investigated during the Finokalia Aerosol Measurement Experiments in 2008 and 2009 (FAME-2008 and FAME-2009). The multi-component aerosol dynamics model was used to derive volatility distributions from the measurements and was used to compare the results from FAME-2008 and 2009.;A new version of the thermodenuder, suitable for field measurements, was developed. The newly developed thermodenuder system is able to switch between residence times in the heating zone automatically. It was tested with a single-component aerosol and was compared with the original field thermodenuder system. The improved TD will aid in future field measurements and help broaden our knowledge on the volatility of organic aerosols.;The TD system and the aerosol dynamic model were applied to various secondary organic aerosol (SOA) systems. Volatility of SOA produced from the ozonolysis of alpha-pinene, beta-pinene and limonene, at low and intermediate relative humidity, and at low and high NOx conditions was investigated. The behavior of the SOA in the thermodenuder was reproduced accurately using the dynamics model based on the volatility basis-set approach.