Does anyone have any details on what kind of filter this was? I bought a relatively high-MERV filter for my home, but I’m wondering what I should actually be trying to filter out.
MERV 13's are optimal for particle removal because compared to a HEPA some of the removal requires multiple passes but the filters are a lot less restrictive and allow higher airflow. Corsi and Rosenthal looked into this with the CR box and came to the conclusion its technically faster at clearing a room than using HEPA standard filters. For infections and damaging PM2.5 particles mechanical filtration with MERV13 is the best you are going to get.
You could also add potentially get a HEPA with a carbon filter which will get rid of volatile organic compounds which can also be damaging (but also just be the smell of food) but they don't tend to be as effective and depending on the mix of VOCs verses particles one filter may run out before the other and carbon really doesn't capture all that much or well. It is a good way to get rid of smell at least for a while.
There is a whole world of different standards for filtration for industrial and hazard chemicals which the FFP2/3 and N95 standards for Personal Protective Equipment respirators will lead you into if you want to go into that rabbit hole, but for a household typically its mostlt about Particulate matter, Volatile organic compounds and CO2. CO2 is about bringing in fresh air from outside.
Then when outside of the household N95/99 or FFP2/3 respitators do the same job in unclean air environments which is basically everywhere, outside or indoors in public places pretty much never meet the World Health Organisations levels for PM2.5 and often exceed CO2 (a proxy for re-breathing and a high change of viral infection spread) standards too.
I didn't see the model specified. They also said some schools got carbon filters, which is a different type of filter.
There's footnote saying many filters weren't even installed because some teachers thought they made the air "too dry", which is major placebo effect at work (air purifiers don't extract moisture from the air).
The entire paper is really not good quality, to be honest.
You can get a small HEPA purifier for a single room to remove particulates. The size of the filter, noise level, and amount of air moved are things to look for. Stepping up to activated carbon would remove VOCs, but cost significantly more (see IQAir, Austin Air, but ignore the cheap models that don't have 10-20lbs or more of activated carbon).
Higher does not necessarily mean better. Higher grade filters filter more in each pass, but can overall provide worse performance as the air flow rate goes down. The air is being recirculated in a portable unit or in a standard domestic ducted heating/cooling situation.
