https://www.epa.gov/indoor-air-quality-iaq/what-merv-rating suggests at least 85%.

Haha yes good point, especially since the chart is what’s relevant to many homes and schools. It can be relevant to a hair dressing school though! It does make you think, because what about hair salons? Between blow dryers and hair product, those workers are breathing in PM2.5 all day!

Roy: You’re right. There’s more water vapor in the air in most places than there is argon or CO2. I looked back at one of my psychrometrics articles for that, and the list there was for the components of dry air. I’ve just added water vapor to that list here. Thanks.