Laboratory performance comparison of respirable samplers

Three respirable samplers (nylon cyclone, SKC cyclone, and foam sampler) were tested for aerosol penetration as a function of aerosol size, to examine the precision and the accuracy with respect to the newly defined respirable convention. An ultrasonic atomizing nozzle was used to generate micrometer- sized liquid dioctylphthalate or solid potassium sodium tartrate aerosol particles, with count median diameters of 3 μm or 8 μm, and geometric standard deviation of 1.6, depending on the properties of the solution to be nebulized. The aerosol number concentration and size distribution upstream and downstream of the samplers were measured by using an aerodynamic particle sizer, which was calibrated against a settling velocity chamber. The results showed that a newly developed foam sampler meets the requirements of the 50% cutoff size as well as the slope of the international respirable convention. For considering both the accuracy and precision of the samplers, it may be inappropriate to select the estimator with least variance or to pick the estimator with least bias. Instead, the concept of the mean square error (MSE) should be applied, because it leads to the best combination of small bias and small variance. Analysis of MSE showed that the foam sampler performed better than the cyclone samplers, if the challenge aerosol was liquid. For solid particles larger than 6 μm, the foam samplers apparently experienced significant particle bounce off and became less precise and less accurate as compared with the cyclones.