Abstract View
Improvement on Differential Mobility Analyzer Method for Estimation of the Enthalpy of Vaporization Using an Algorithm to Derive Particle Size Changes from Full-Size Distribution
CHIRANJIVI BHATTARAI, Andrey Khlystov, Desert Research Institute
Abstract Number: 312
Working Group: Instrumentation and Methods
Abstract
One of the most popular methods for studying the volatility properties of an aerosol is the tendem differential mobility analyzer (TDMA) technique. In the TDMA method, a narrow size range of particles is selected by a front differential mobility analyzer (DMA) and is exposed to an elevated temperature in a thermodenuder causing particles to evaporate. The size distribution of the evaporated aerosols is then measured with a second DMA and the mean or mode size is used to derive aerosol thermodynamic properties. The TDMA method usually takes a relatively long time to acquire sufficient data, as several sizes at several temperatures need to be measured consecutively. Here, we report a more efficient approach for determination of enthalpy of vaporization of single component aerosols using the TDMA method. In this method, size changes of all particles transmitted by the front DMA are measured at an elevated temperature point (45 oC). An inversion algorithm is then applied to the original and evaporated size distributions to derive size changes at individual aerosol size bins. The algorithm was developed by Heisler and co-workers in 1976 and is based on the preservation of particle number concentration. We performed a detailed theoretical and numerical analysis of the uncertainties associated with the inversion algorithm and verified it experimentally using an adipic acid aerosol. The algorithm applied to broad size distribution measurements provided results that are within 10 % of the TDMA measurements. We will describe the theoretical basis for derivation of the enthalpy of vaporization from measurements of size changes at several size bins without assumptions on the evaporation coefficient. Enthalpy of vaporization for adipic acid and pimelic acids determined with this method is 117 and 100 kJ/mol, respectively. This compares well with the available literature data (95 --154 and 80 --162 kJ/mol, respectively).