Abstract

Airborne transmission of SARS-CoV-2 through virus-containing aerosol particles has been established as an important pathway for Covid-19 infection. Suitable measures to prevent such infections are imperative, especially in situations when a high number of persons convene in closed rooms. Here we tested the efficiency and practicability of operating four air purifiers equipped with HEPA filters in a high school classroom while regular classes were taking place. We monitored the aerosol number concentration for particles >3 nm at two locations in the room, the aerosol size distribution in the range from 10 nm to 10 µm, PM₁₀ and CO₂ concentration. For comparison, we performed similar measurements in a neighboring classroom without purifiers. In times when classes were conducted with windows and door closed, the aerosol concentration was reduced by more than 90% within less than 30 min when running the purifiers (air exchange rate 5.5 h⁻¹). The reduction was homogeneous throughout the room and for all particle sizes. The measurements are supplemented by a calculation estimating the maximum concentration levels of virus-containing aerosol from a highly contagious person speaking in a closed room with and without air purifiers. Measurements and calculation demonstrate that air purifiers potentially represent a well-suited measure to reduce the risks of airborne transmission of SARS-CoV-2 substantially. Staying for 2 h in a closed room with a highly infective person, we estimate that the inhaled dose is reduced by a factor of six when using air purifiers with a total air exchange rate of 5.7 h⁻¹.

摘要

SARS-CoV-2通过含病毒的气溶胶颗粒在空气中的传播已被确定为Covid-19感染的重要途径。必须采取适当的措施来防止此类感染，特别是在大量人员聚集在封闭房间中的情况下。在这里，我们在定期上课的同时，在高中教室中测试了运行四台装有HEPA过滤器的空气净化器的效率和实用性。我们在房间中的两个位置监控了大于3 nm的颗粒的气溶胶浓度，气溶胶尺寸分布范围为10 nm至10 µm，PM ₁₀和CO ₂专注。为了进行比较，我们在没有净化器的相邻教室中进行了类似的测量。在关闭门窗的情况下上课的时间里，运行净化器后不到30分钟内气溶胶浓度降低了90％以上（空气交换速率为5.5 h ^-1）。在整个房间内和所有粒径下，还原作用都是均匀的。在测量的基础上，通过计算来估计在一个有空气净化器和没有空气净化器的密闭房间中，来自具有高度传染性的人的含病毒气溶胶的最大浓度水平。测量和计算表明，空气净化器可能是一种适合的措施，可以从实质上降低SARS-CoV-2的空中传播风险。我们在一个有高传染性人的封闭房间里呆了2小时，我们估计当使用空气净化器的总空气交换率为5.7 h ^-1时，吸入剂量减少了六倍。