A Method For Measuring The Vapour Pressures Of Pah'S Adsorbed On The Surface Of Soot

Abstract

A new method is reported that utilizes a low-temperature quartz microbalance in combination with Knudsen cells to obtain adsorption isotherms for substances with very low equilibrium pressures (< 10^?5 Pa). The method allows for the first time to measure directly thermodynamic properties of important aerosol/pollutant systems at typical environmental temperatures. Application is demonstrated by an investigation of fluoranthene and pyrene adsorbed on carbon aerosol particles (T = 293.15 K?302.13 K). Both PAHs are unable to form extended multilayers on the surface. Slightly above monolayer coverage the three-dimensional crystalline solid phase is thermodynamically more stable.