Undulating Multislit Impactor in Ultrahigh-Volume Aerosol Sampler to Reduce Filter Clogging

Ultrahigh-volume samplers with a flow rate of approximately $500{\mathrm{m}}^3/\mathrm{h}$ are widely used for atmospheric radionuclide monitoring. These samplers are often shut down during heavy particulate pollution due to filter clogging. We proposed a solution involving sampling with an impactor to reduce the filter clogging and avoid sample loss. A multislit impactor was designed to keep its low pressure drop and to save space in the context of an ultrahigh flow rate. Nonwoven cloth was chosen as impaction substrate for a low cut size, high dust capacity, and convenient operation. An undulating jet plate was designed to reduce particle loss on its surface and this was predicted by computational fluid dynamics (CFD). The test experiment results show that the cut size of the impactor is approximately 1.5 μm, and the particle loss is only 5% with loess aerosol as the challenge. Field tests show that the atmospheric large particles collected by the impactor was average approximately 0.53; the concentrations of ${}^{131}\mathrm{I}$ and aerosol mass are consistent with those from commercial Hi-Vol total suspended particles (TSP) sampler ($63{\mathrm{m}}^3/\mathrm{h}$) by $\pm 10\%$. Results from the laboratory and field tests suggest that the impactor presented in this study constitutes a major improvement in the reduction of the filter clogging in ultrahigh-volume aerosol samplers under heavy particulate pollution.