AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
A Method to Estimate the Bipolar Ion Mobility Ratio and Charge Fractions of Submicron Particles in an Aerosol Neutralizer
XIAOTONG CHEN, Jingkun Jiang, Tsinghua University
Abstract Number: 69 Working Group: Instrumentation and Methods
Abstract Electrical mobility size spectrometer is widely used in aerosol science. Among its three key components (i.e., bipolar charger (neutralizer), electrical mobility classifier, and detector), more attention has been given to the latter two in recent years and good progress was made. Progress in understanding and reducing the measurement uncertainties caused by the charger is slow. Recent studies revealed that trace species in the carrying gas can lead to significant variations in the mobility of ions produced in the charger. Accordingly, aerosol charge fractions after the neutralizer may deviate from values predicted by a widely used formula. In this study, we proposed a method to estimate the mobility ratio of positive and negative ions produced by a neutralizer based on measured positively and negatively charged particles by an electrical mobility size spectrometer. A modified equation from Gunn and Woessner (1956) was used to calculate aerosol charge fractions from the ion mobility ratio. The estimated charge fractions can then be used in data inversion to achieve more accurate measurement of aerosol size distributions. This method was evaluated using simulated aerosols and laboratory-generated aerosols.