Real-time measurement of submicron aerosol particles having a log-normal size distribution by simultaneously using unipolar diffusion charger and unipolar field charger

Recently, Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430] have introduced a methodology for performing simple and fast measurements of submicron aerosol particles having a log-normal size distribution, using a unipolar diffusion charger, an electrometer, and a condensation particle counter (CPC). The methodology can be applied to particles of 30-700 nm and requires an assumption of their geometric standard deviation in size. In this paper we propose a much cheaper but faster method which involves substituting a unipolar field charger and another electrometer for the CPC. With the data obtained using this dual-charger system, we developed a data inversion algorithm and estimated the particle size distribution by minimizing the differences between the measured aerosol currents and the calculated values. To compare the size distribution with the data measured using a scanning mobility particle sizer (SMPS), sodium chloride (NaCl) particles smaller than 0.1 μ m in diameter, and dioctyl sebacate (DOS) particles with a diameter of 0.1-0.7 μ m, were used. The estimated results for the NaCl and DOS particles were within 10% of the data measured with the SMPS, while a 33% deviation from the SMPS results was obtained in Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430]. Furthermore, the detection time obtained with the use of our dual-charger system was faster (< 3 s) than the 5 s obtained by Park et al. [(2007). Development and performance test of a unipolar diffusion charger for real-time measurements of submicron aerosol particles having a log-normal size distribution. Journal of Aerosol Science, 38, 420-430].