Determination of Effective Density of Sub-Micron Size Using Pre-Determined SMPS Data
Jaeho Oh, Jungho Hwang, JEONG HOON BYEON, School of Mechanical Engineering at Yeungnam University
Abstract Number: 304
Working Group: Instrumentation and Methods
Abstract
Particle effective density is a parameter for combining particle bulk density and shape of aerosol particles. It is employed to convert the number-based concentration to a mass-based concentration and to ascertain the relationship between the aerodynamic and Stokes diameters.
Effective density is often determined by utilizing a DMA to classify particles based on electrical mobility, followed by serial mass measurements with an aerosol particle mass analyzer (APM) or aerodynamic diameter measurements with an electric low-pressure impactor (ELPI).
Since the ambient atmosphere is a low-particle concentration environment, it is problematic that using a DMA for classification based on electrical mobility diameter will result in a lower resolution because of the extremely low number concentration emitted by the DMA's efficiency.
A corona charger used in Hyun et al. (2015) and a lab-made two-stage low-pressure impactor with a 130 nm cut-diameter were used in this investigation to assess the effective density.
SMPS is used in this investigation to determine the size distribution, and measurements of the current carried by charged particles were made both upstream and downstream of the impactor following corona charger. By assuming an arbitrary effective density, the previous study transformed the particle size distribution into an aerodynamic diameter-based distribution (DeCarlo et al., 2004).
where, is the effective density, is the density of water (1 g/cm3), d is the particle diameter, C is the slip correction factor and subscript m and a refer to mobility and aerodynamic, respectively.
Particle size distribution of downstream of the impactor was obtained by calculating the collection efficiency of the impactor from particle size distribution of upstream of the impactor.
For the both particle size distribution of upstream and downstream, theoretical current were calculated using charging theory presented in Hinds, (1999). By comparing the calculated current and the measured current, the effective density was iteratively assumed and the effective density that minimizes the difference between current was determined.
Acknowledgements: This research was supported by the Korea Environment Industry and Technology Institute (KEITI) through the Technology Development Project for Biological Hazards Management in Indoor Air, funded by the Korea Ministry of Environment (MOE) (No.2021003370005).
References
[1] DeCarlo, P. F., Slowik, J. G., Worsnop, D. R., Davidovits, P., & Jimenez, J. L. (2004). Particle morphology and density characterization by combined mobility and aerodynamic diameter measurements. Part 1: Theory. Aerosol Science and Technology, 38(12), 1185-1205.
[2] Hinds, W. C., & Zhu, Y. (1999). Aerosol technology: properties, behavior, and measurement of airborne particles. John Wiley & Sons.
[3]Hyun, J., Nasr, A. M., Choi, N. K., Park, D., & Hwang, J. (2015). Design and Performance Test of a Lab-Made Single-Stage Low-Pressure Impactor for Morphology Analysis of Diesel Exhaust Particles. Aerosol Science and Technology, 49(10), 895-901.