Determining Aerosol Volatility Parameters Using a “Dual Thermodenuder” System: Application to Laboratory-Generated Organic Aerosols

Abstract

Thermodenuders (TD) are a tool widely used for measuring aerosol volatility in the laboratory and field. Extracting the parameters that dictate organic aerosol volatility from TD data is challenging because gas-particle partitioning rarely reaches equilibrium inside a TD operating under atmospheric conditions, thus a wide variety of parameter sets can explain observed evaporation. Component volatilities (as represented by saturation vapor pressure, Csat), cannot be directly extracted due to uncertainties in potential limitations to mass transfer (represented by mass accommodation coefficient, α) and components’ enthalpies of evaporation (ΔHvap). To address these limitations, we have developed a “dual TD” experimental approach in which one line uses a temperature-stepping TD (TS-TD) with a relatively long residence time (RT) and the other operates isothermally at variable residence time (VRT-TD). Data from this approach are used in tandem with an optimizing evaporation kinetics model to extract the values ...