Collecting Particulate Matter and Particle-Bound Polycyclic Aromatic Hydrocarbons Using a Cylindrical Thermal Precipitator

Abstract

Thermophoresis has been used to develop various thermal precipitators; however, their collection performance for ambient particulate matter (PM) with an aerodynamic diameter less than 10 μm (PM10) has been rarely reported, and the effect of the temperature gradient adopted in the precipitator on the evaporation loss of the organic fraction of collected particles has not been discussed to the authors’ knowledge. In this study, a cylindrical thermal precipitator consisting of two coaxially aligned cylinders with an annular space of 0.51 mm and a two-inlet impactor was designed for collecting PM10. The effects of the sampling flow rate and temperature gradient on the collection efficiency were examined. The precipitator was also tested for its collection efficiency for particle-bound polycyclic aromatic hydrocarbons (PAHs). At a temperature gradient of 72.6°C/mm and a flow rate of 7.74 L/min, the collection efficiency could reach 100% for PM with an electrical mobility diameter (Dp)<0.5 μm and decreased gradually to 70% as Dp increased from 0.5 to 1.0 μm. For PM with Dp>1.0 μm, the collection efficiency increased due to impaction at the inlet. The collection efficiency increased with an increase in the temperature gradient or a decrease in the inlet flow rate. The semiempirical model could reasonably fit the collection efficiency curve of the precipitator. No significant evaporation loss of PAHs was found when the temperature of the cold cylinder surface was approximately 0°C. It was concluded that the thermal precipitator could be used to collect ambient fine PM with a size less than 0.5 μm, and the inlet impactor design could improve the collection efficiency for coarse particles.