This. There have also been tons of experiments, starting with the Atlanta olympics, where external pollution sources get throttled and you can see a very clear

This. There have also been tons of experiments, starting with the Atlanta olympics, where external pollution sources get throttled and you can see a very clear and immediate drop in cardiovascular-related deaths. Also there are plenty of standalone units that don’t integrate with HVAC. E.g. I have the Winnex 5300-2, which is one of the Amazon recommended units. (Some of the others are designed for smokers, chefs, or other specialized purposes.)