Department of Civil and Environmental Engineering, University of California Davis, 1 Shields Ave., Davis, CA, 95616, USA.
Department of Chemical Engineering, University of California Davis, 1 Shields Ave., Davis, CA, 95616, USA.
Sci Rep. 2021 Jun 8;11(1):12110. doi: 10.1038/s41598-021-91487-7.
Wearing surgical masks or other similar face coverings can reduce the emission of expiratory particles produced via breathing, talking, coughing, or sneezing. Although it is well established that some fraction of the expiratory airflow leaks around the edges of the mask, it is unclear how these leakage airflows affect the overall efficiency with which masks block emission of expiratory aerosol particles. Here, we show experimentally that the aerosol particle concentrations in the leakage airflows around a surgical mask are reduced compared to no mask wearing, with the magnitude of reduction dependent on the direction of escape (out the top, the sides, or the bottom). Because the actual leakage flowrate in each direction is difficult to measure, we use a Monte Carlo approach to estimate flow-corrected particle emission rates for particles having diameters in the range 0.5-20 μm. in all orientations. From these, we derive a flow-weighted overall number-based particle removal efficiency for the mask. The overall mask efficiency, accounting both for air that passes through the mask and for leakage flows, is reduced compared to the through-mask filtration efficiency, from 93 to 70% for talking, but from only 94-90% for coughing. These results demonstrate that leakage flows due to imperfect sealing do decrease mask efficiencies for reducing emission of expiratory particles, but even with such leakage surgical masks provide substantial control.
佩戴手术口罩或其他类似的面部遮盖物可以减少通过呼吸、说话、咳嗽或打喷嚏产生的呼气粒子的排放。虽然已经证实口罩边缘会有一部分呼出气流泄漏，但目前尚不清楚这些泄漏气流如何影响口罩阻挡呼气气溶胶粒子排放的整体效率。在这里，我们通过实验表明，与不戴口罩相比，手术口罩周围泄漏气流中的气溶胶粒子浓度降低，其降低幅度取决于逃逸方向（顶部、侧面或底部）。由于难以测量每个方向的实际泄漏流量，我们使用蒙特卡罗方法来估计粒径在 0.5-20 μm 范围内的粒子在所有方向上的流量校正后的粒子排放率。从这些数据中，我们推导出口罩的流量加权整体基于数量的粒子去除效率。考虑到通过口罩的空气和泄漏气流，口罩的整体效率（包括通过口罩的空气和泄漏气流）比口罩的过滤效率降低，说话时从 93%降至 70%，但咳嗽时仅从 94%降至 90%。这些结果表明，由于密封不完美导致的泄漏气流确实会降低口罩减少呼气粒子排放的效率，但即使存在这种泄漏，手术口罩仍能提供实质性的控制。
