10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Measurement of Effective Density of Submicron-sized Ambient Aerosols Using a Lab-made Single Stage Low-pressure Impactor with Scanning Mobility Particle Sizer
JANG-SEOP HAN, Junho Hyun, Jungho Hwang, Yonsei University, Korea
Abstract Number: 1142 Working Group: Instrumentation
Abstract The structure of particles is directly related to their transport properties and plays an important role in determining their deposition pattern in the human respiratory system. Previous studies report that agglomerate particles can deposit on human lung more easily than spherical particles since the specific surface area of the agglomerate particles is larger than that of spherical particles (Morawska et al., 2005; Scheckman and McMurry, 2011). The particle effective density is a parameter that describes the combined effects of particle density and shape upon aerosol motion.
To measure the particle effective density, it is typical to use two instruments connected in series. Kelly and McMurry (1992) introduced a basic approach used in this methods and utilized this technique to analyze lab-generated particles. They used a differential mobility analyzer (DMA) and a microorifice uniform deposit impactor (MOUDI) with known cutoff diameters. To measure the effective density of DEPs, Maricq and Xu (2004) and Van Gulijk et al. (2004) used an electrical low-pressure impactor (ELPI). In their works, DEPs were classified by DMA, then brought to ELPI with which the aerodynamic diameter of DEPs was measured. Park et al. (2003) also used a DMA but they used an aerosol particle mass analyzer (APM) instead of ELPI. For each APM voltage, the particle number concentration was measured with a condensation particle counter (CPC), and the peak APM voltage, which corresponds to the peak mass for the mobility-selected particles, was determined. The particle effective density was obtained by carrying out sequential measurements on DEPs and polystyrene latex (PSL) spheres of the same mobility size.
In this paper, a new methodology was developed by using a low-pressure impactor and SMPS to obtain the effective density of ambient aerosol particles. The low-pressure impactor, a corona charger and aerosol electrometer was used for the electrical current, and SMPS measured the size distribution of the aerosol. The mobility diameter measured from SMPS was changed into aerodynamic diameter with assumed effective density, then the number concentration was estimated using efficiency of the impactor. The currents were calculated with the estimated number concentration and compared with the measured value. The methodology was validated with lab-generated sodium chloride (NaCl) particle then the effective density was obtained from various places.
Outdoor particles had similar effective density about 0.81 to 0.91. Indoor aerosols had different effective densities – 1.83 for the office A, 0.6 for the office B, 0.69 for the house, 1.06 for the underground parking lot. The size distributions of particles in the office and the house were similar and the effective density were also similar. The geometric mean mobility diameter of particle in the underground parking lot is 25.8 nm. The main source of the underground parking lot is the vehicle exhaust gas. The effective density and size distribution of the office A was very distinct from other places because nanoparticle experiment was performed in this office.
Acknowledgement This research was supported by Korea Ministry of Environment (MOE) as Advanced Technology Program for Environmental Industry.