Determination of evaporation coefficients of semi-volatile organic aerosols using an integrated volume—tandem differential mobility analysis (IV-TDMA) method

We present the integrated volume—tandem differential mobility analysis method for determining evaporation coefficients of semi-volatile aerosols. This thermodenuder-based method allows separate determination of the three parameters governing aerosol evaporation, namely, saturation pressure, surface free energy and evaporation coefficient. Saturation pressure is determined by measuring particle volume changes as the aerosol passes through equilibrium states, while evaporation coefficient and surface free energy are determined by fitting particle evaporation rates measured under non-equilibrium conditions to a numerical model of the evaporation process. Evaporation coefficient is determined in a size range where surface free energy effects are negligible, allowing for single parameter optimization.We demonstrate the technique by applying it to dicarboxylic acid aerosols which are pertinent to atmospheric chemistry problems. We obtained evaporation coefficients and surface free energy values of 0.07±0.020.07±0.02 and 0.15±0.070.15±0.07, 0.08±0.020.08±0.02 and 0.17±0.120.17±0.12 and 0.24±0.040.24±0.04 and 0.23±0.08J/m2 for succinic, adipic, and pimelic acids, respectively.