@j_g_allen @olgakhazan One way masking does work, but two way masking works a lot better. There are inevitably times when people need to take their masks off, masks slip, people who can't wear masks, etc.. Keeping most infectious crap out of the air to start better than trying to filter it out later.
@j_g_艾伦@olgakhazan单向掩蔽确实有效，但双向掩蔽效果更好。有时人们不可避免地需要摘下口罩，口罩滑落，不能戴口罩的人等等。。一开始就把最具传染性的垃圾远离空气，比以后再过滤要好。