Derivation of particle-size changes from polydisperse size distribution measurements: numerical and experimental verification

Abstract

Measurements of particle-size transformations due to changes in temperature, relative humidity, and other environmental factors are essential for understanding aerosol properties, such as its hygroscopicity and volatility. The commonly used measurement techniques, such as tandem differential mobility analyzer (TDMA) and single-particle levitation techniques, allow measurements of only one initial size at a time, which makes their applications to highly dynamic aerosol systems problematic. In this paper, we evaluate the Heisler method developed in the second half of 1970s that uses measurements of size distributions of a polydisperse aerosol before and after it undergoes a growth or evaporation. The Heisler method is based on preservation of particle number concentration and allows simultaneous determination of particle-size changes across the whole measured size distribution. In this paper, we evaluated the Heisler method using numerical techniques and compared it with TDMA measurements during experiments with adipic acid aerosol. We show that the Heisler method is sensitive to counting statistics and that significant errors (over 50%) can occur if there are particles that can grow or evaporate in or out of the measured size range. Otherwise, the Heisler method gives results within 5% of those obtained with TDMA measurements, providing a faster alternative to the TDMA technique.