New type of impactor with varying impaction plate temperature for capturing particulate matters

Abstract

Impactors are the most widely used particle size-selective samplers. These are not only sampling devices but also aerosol classifiers. Impactors use the particle inertia to sample and classify aerosols. When an impactor is used, an impaction plate is greased with a coating material to prevent reentrainment and to obtain higher efficiency. However, for bioaerosols, it may be impractical to use a coating material since it can cause viability loss and contamination of bioaerosols. And the work of coating is inaccurate and burdensome. However, without the coating material, the performance of an impactor is inadequate - a problem which necessitates this research. In this study, we experimentally show the effect of impaction plate temperature change on the impactor performance. The impaction plate was cooled or heated with the thermoelectric module in the impactor. The temperature of the impaction plate was then monitored by the thermocouple connected to the impaction plate. Comparisons among the results reveal that cooling the impaction plate makes the impactor collection efficiency higher and the re-entrainment lower. Therefore, the collection efficiency curve becomes steeper, illustrating the increased effectiveness. To elucidate the reason of these phenomena, we designed two kinds of experiments and got the reasonable results. It was found that the condensation effect was the dominant mechanism in reducing rebounce in the cooled plate impactor rather than the thermophoresis effect. And this kind of impactor could be applied to PM2.5 classification. To show the application of this kind of impactor, we sampled the bioaerosols by this impactor. E.coli and B.subtilis bacteria bioaerosols were used for the experiments. Based on the study, a new type of impactor with a thermoelectrically cooled plate is proposed, and is demonstrated to work well in these experimental conditions.