That works for particulates but not gasses like carbon monoxide. You’re better off having the best filters you can get supplying fresh air constantly rather than constantly recirculating stale air.
Carbon monoxide comes from vehicle exhaust, so the levels are still lower outside cities and off high-traffic roads. I'd rather recirculate my "stored up" clean air vs. pull in CO from the line of cars stopped ahead of me. I just involves being aware of the surroundings.
Ideally a controller would monitor the outside CO/PM and inside CO2 to control the recirculate door.
> Location is generally less important than wind direction here
My experience (and my nose) strongly disagrees with this assertion. YMMV.
The urban-vs-rural divide in my area is shockingly detectable just by the smell of combustion byproducts alone.
> you aren’t tracking [wind direction]
Who says I'm not? Tall flagpoles make for nice, ubiquitous windsocks. I wouldn't use it to land a plane, but for this purpose it works just fine.
And yes, it's absolutely a hard problem. Just look at all the ink I've spilled...
The human nose (especially mine) is still a remarkable chemical sensor, with only a few blind spots. In practice the major blind spots, namely CO, correlate well with detectable combustion byproducts. I appreciate your concern, but you worry for no good reason!
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I'll share one final trick, which should be pretty obvious: avoid sucking in the packet of air a bunch of cars (or one diesel truck) just accelerated through. In practice, usually this means turning on recirculate when stopping behind a line of cars, and then waiting to turn off recirculate until a short distance after going through the light.
Just to preempt the seemingly-inevitable negativity reflex: if you don't believe such hyper-local variations in pollution make a big difference, I guess you've never cycled before. ;)
Urban/suburban areas provide a different variety of smells which is easy to confuse with overall toxicity levels. Chemical sensors will sometimes line up with your expectations and other times be very different.
Trust me, I know what vehicle exhaust smells like. ;)
Living outside the city, I'm not constantly fatigued to its odors. So that's not a factor.
But more to my original point, it disproves the "wind > location" idea (in my geography), since odor acts as a tracer for packets of air coming from the city.
I wish I could calm your anxiety, but on the bright side I am truly touched by your outpouring of concern for my respiratory well-being! Thank you, kind stranger.
You seem to misunderstand, Olfactory fatigue is very fast. When people fart for example the perception of smell goes away vastly sooner than the actual smell.
If you’re trying to judge air concentrations based on how intense the smell, it simply doesn’t work.
I'm judging the presence of air pollutants. If I can smell it (ie above the lower detection limit), then I know I'm being exposed.
The converse is not necessarily true of course, but I can do this without hundreds of dollars in sensors. "Do what you can, where you are, with what you've got."
To account for sub-detectable pollution levels, I generally give myself a little extra buffer room. If I observe that detectable pollution odors begin at a certain point, I'll engage recirculate a half-mile before.
Generally nowadays I successfully avoid any detectable pollution/proxy odors, using the sort of preemptive planning I've described. You should try it!
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TL;DR this whole thread: recirculate gives better air quality, just flush CO2 periodically, ideally when in relatively cleaner air
Moving from constant levels of pollution to intermittent levels of population you notice ever stronger smells even as things improve. The reverse is also true, going from intermittent smells to constant toxicity it seems like things are improving.
This is the case because you most easily notice rapid changes not overall levels.
And again, both articles ignore the possibility of having better filters.
Not really. What I currently do prevents any health flare-ups, so it's working for me.
I might be effected by sub-detectable levels of pollution. I definitely would be effected by detectable levels of pollution. So I know I'm better off, which makes me happy.
I do not confuse this with perfection, but this level of cost/benefit tradeoff is "good enough" for me. Some of these tricks might be helpful for other people too!
> Moving from constant levels of pollution to intermittent levels of [pollution]
This is not my situation.
> And again, both articles ignore the possibility of having better filters.
I didn't write the articles, I just cited them to support the fact that recirculate results in lower pollution levels in cars.
I, in my life, very much do not ignore air filters. :)
> recirculating results in lower <particulate> pollution < and higher non particulate pollution>
Again, assuming inadequate filters, better filters invalidate their results.
> sub detectable
This is very much detectable, we just ignore it. Come back from a long trip to a remote enough area and it’s shocking how much everything smells, even small country roads briefly stink of pollution.
But, I think the dead horse has been beaten enough at this point.
> 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?
> 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.
