It's not that simple because any filtration media that will filter out, e.g., diesel exhaust or pollen will lyse the bacteria that are always floating in the air, thereby adding to the air that leaves the filtration device the lipopolysaccharide (LPS) toxin that without the action of the filtration device would remain relatively-safely inside the bacterium. Yes, even without any air purifiers, you will absorb some LPS toxin from the bacteria in the air you breath, but running an air purifier approximately doubles the dose. I claim to be able to tell the difference in that when I'm in a small room with an air purifier running at high fan speed, I am much more likely to feel a certain kind of non-severe, but not-good headache-like feeling.
I.e., you don't want to run an air purifier that removes very small particles from the air when you don't need to -- at least if you are as sensitive to LPS as I am. And you don't want the fan speed of the purifier's being higher than necessary.
I'm gonna need a source on that, as the only relevant thing that comes up on a search for "lipopolysaccharide toxin air filter" is a single study [0] that tested a single air purifier (whose filter had not been changed in a year) in a single room. It includes the telling phrase: "The conclusions here, however, should be interpreted cautiously due to the small sample size here."
It can be more complicated, yes. I assert that it usually isn't. You don't spend time worrying as much about what the contaminants are, you just drive them to zero.
I grant the point that you don't want to just stir up the air. Which is why you don't just run a fan, necessarily.
It's not that simple because any filtration media that will filter out, e.g., diesel exhaust or pollen will lyse the bacteria that are always floating in the air, thereby adding to the air that leaves the filtration device the lipopolysaccharide (LPS) toxin that without the action of the filtration device would remain relatively-safely inside the bacterium. Yes, even without any air purifiers, you will absorb some LPS toxin from the bacteria in the air you breath, but running an air purifier approximately doubles the dose. I claim to be able to tell the difference in that when I'm in a small room with an air purifier running at high fan speed, I am much more likely to feel a certain kind of non-severe, but not-good headache-like feeling.
I.e., you don't want to run an air purifier that removes very small particles from the air when you don't need to -- at least if you are as sensitive to LPS as I am. And you don't want the fan speed of the purifier's being higher than necessary.