Characterization of a Particle Thermodenuder for the Analysis of Aerosol Volatility and Composition

Cheol-Heon Jeong (1), Greg J. Evans (1), W. Richard Leaitch (2), John Liggio (2)

(1) Southern Ontario Centre for Atmospheric Aerosol Research, University of Toronto, Toronto, Canada (2) Science and Technology Branch, Environment Canada, Toronto, Canada

     Abstract Number: 654
     Last modified: May 14, 2010

Abstract
Studies of aerosol volatility provide indirect information on particle composition for a better understanding of particle toxicity and evolution in the atmosphere. The volatile and non-volatile fractions of atmospheric particles are often measured using a thermodenuder (TD, Dekati Ltd). Particle losses caused by diffusional and thermophoretic processes inside a TD were theoretically and experimentally evaluated for various temperatures (30ºC - 250ºC) and particle sizes (15 nm - 100 nm) at two flow rates (0.6 l/min and 10 l/min). Overall, the experimental penetration efficiencies were in good agreement with theoretical estimates. With deceasing particle size and increasing temperature, the penetration efficiency decreased due to particle diffusion and thermophoretic losses. Longer residence time (0.6 l/min) in a TD resulted in poorer particle penetration. Particle losses in the 40-100 nm size range at 30ºC were negligible at 10 l/min, while the penetration efficiency at 0.6 l/min ranged from 85 to 90%. At 250ºC, the penetration efficiencies were about ~76% and ~59% at 10 l/min and 0.6 l/min, respectively.
Number concentrations and size distributions of ambient particles were measured by using parallel a Fast Mobility Particle Sizer (FMPS, TSI 3091) and TD-FMPS system in parallel at urban and rural sites. The combination of the TD with the rapid size spectrometers provided the overall size distributions corresponding to the volatile/non-volatile particles every second. In addition, a thermodenuder Aerosol Time-of-Flight Mass Spectrometer (TD-ATOFMS, TSI 3800) was used to chemically characterize the non-volatile fractions. The fraction of volatile/non-volatile materials in the particles was estimated as a function of particle size and the two sites were compared.