Sheng-Chieh Chen

A novel active personal nanoparticle sampler (PENS), which enables the collection of both respirable particulate mass (RPM) and nanoparticles (NPs) simultaneously, was developed to meet the critical demand for personal sampling of engineered nanomaterials (ENMs) in workplaces. The PENS consists of a respirable cyclone and a micro-orifice impactor with the cutoff aerodynamic diameter (d(pa50)) of 4 μm and 100 nm, respectively. The micro-orifice impactor has a fixed micro-orifice plate (137 nozzles of 55 μm in the inner diameter) and a rotating, silicone oil-coated Teflon filter substrate at 1 rpm to achieve a uniform particle deposition and avoid solid particle bounce. A final filter is used after the impactor to collect the NPs. Calibration results show that the d(pa50) of the respirable cyclone and the micro-orifice impactor are 3.92 ± 0.22 μm and 101.4 ± 0.1 nm, respectively. The d(pa50) at the loaded micro-Al(2)O(3) mass of 0.36-3.18 mg is shifted to 102.9-101.2 nm, respectively, while it is shifted to 98.9-97.8 nm at the loaded nano-TiO(2) mass of 0.92-1.78 mg, respectively. That is, the shift of d(pa50) due to solid particle loading is small if the PENS is not overloaded. Both NPs and RPM concentrations were found to agree well with those of the IOSH respirable cyclone and MOUDI. By using the present PENS, the collected samples can be further analyzed for chemical species concentrations besides gravimetric analysis to determine the actual exposure concentrations of ENMs in both RPM and NPs fractions in workplaces, which are often influenced by the background or incident pollution sources.

In this study, an efficient parallel-plate single-stage wet electrostatic precipitator (wet ESP) with a width of 75 mm, effective precipitation length of 48 mm and gap of 9.0 mm was designed and tested to control fine and nanosized particles without the need of rapping. The collection plates are made of sand-blasted copper plates coated with TiO2 nanopowder instead of hydrophilic membranes. Three gold wires (diameter: 100 μ m) were used as the discharge electrodes and a pulse jet valve was used to regularly purge the wires. The design of the present wet ESP is aimed at solving the problems of traditional dry ESPs: reduction of the collection efficiency due to particle deposition on the discharge electrodes and collection electrodes, back corona, and particle re-entrainment. The collection efficiency at initially clean and heavy particle loading conditions was tested and compared to a similar dry ESP. Experimental results showed that when the wet ESP was initially clean, the particle collection efficiency ranged from 96.9–99.7% for particles ranging from 16.8 to 615 nm in electrical mobility diameter at an aerosol flow rate of 5 L/min (residence time of 0.39 s) and an applied voltage of 4.3 kV. After heavy loading with TiO2 nanopowder about 1.2 ± 0.06 g/plate, the collection efficiency of the present wet ESP for corn oil particles was shown to reduce only slightly to 94.7–99.0% for particles from 16.8 to 615 nm in diameter.