[schiffern]

> This is very much detectable, we just ignore it.

Nevertheless, sub-detectable levels we can ignore are lower than sub-detectable levels we can't ignore. So I'm still better off than I would be otherwise. How is this so hard to understand?

You're letting perfect be the enemy of good. This is the critical point you've been ignoring this whole time. All the horse beating could have been avoided! ;)

> recirculating results in lower <particulate> pollution < and higher non particulate pollution>

Your "non particulate pollution" is just exhaled CO2. This is covered when I mention periodic flush of air. For obvious reasons, the editor inside me didn't feel the need to mention CO2 twice (especially not via muddy language like "non particulate pollution") in what is supposed to be a TLDR.

You should clarify, not obfuscate. Listening to your advice, it's confusing whether to prefer having recirculate on or off. You failed to clearly convey the most critical piece of information.

> better filters invalidate their results

"Better" is vague, so this advice is un-actionable.

Without citation I can only assume you just mean bioweapon defense mode, correct?

[Retric]

There isn’t a level of smell you can’t quickly ignore.

> Your "non particulate pollution" is just exhaled CO2.

No, it’s carbon monoxide, NOx, SOx compounds etc. Opening your vents when you stop noticing smells makes things worse.

[schiffern]

> There isn’t a level of smell you can’t quickly ignore.

Not a fixed level, of course! But at any given instant, the level you can ignore is lower than the one you can't. Hence I'm still better off doing this, a fact which apparently you can't stand for some weird reason...

You're also going to gather data over time, which will tend to smooth out any such day-to-day variations.

This is how you can reduce (not eliminate) pollution exposure without paying for expensive non-nose sensors. This is true whether you Believe It Or Not™.

>No, it’s carbon monoxide, NOx, SOx compounds etc.

Citation desperately needed. I showed you mine, you show me yours!

What conceivable mechanism could concentrate these traffic pollutants higher than the outside concentration? Are you running a pump that's somehow fighting entropy to push these outside traffic pollutants (against the alleged concentration gradient) into your car??

Usually it helps if your claim doesn't violate the laws of thermodynamics. :D

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edit: I'll throw you a bone to save time. Literally the only way to achieve this outcome without violating physics is to intentionally reverse my recommendation: try to suck in only the most polluted urban air (intake the concentrated plume from a line of cars accelerating, behind a garbage truck or schoolbus, etc), and then switch to recirculate to save up that highly polluted air and breathe it for as long as possible.

So...... don't do that! If you're studying IAQ in cars, you need to control for that.