[bsenftner]

Opening a car window or running air not on recirc immediately drops the readings to safe levels. I also noticed when in the Uber returning from the airport, the air was in the high 3000's and I explained to the driver, he opened all the windows and I think I scared him a bit.

[schiffern]

Note that, to minimize pollution from vehicle exhaust, you want to set your air to "recirculate". Unsurprisingly, the roadway is where vehicle pollution is most concentrated!

https://www.latimes.com/science/sciencenow/la-xpm-2013-sep-1...

Usually what I do is set it on recirculate, and then every ~10 minutes I periodically "flush" the CO2-laden interior air for a minute or so. Ideally, I'm able to do this "flush" when I'm away from a major city or high-traffic road (and not when driving behind a soot-spewing diesel bus/semi/garbage/cement truck).

I wish there were some way to automate this logic!

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(and yes, my dear observant reader, if I could recirculate "only" 90% of the exterior air it would achieve the same steady-state result, but modern cars got rid of the "slider" that lets you select a percentage of recirculate air... ::sigh::)

[Retric]

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.

[schiffern]

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.

[Retric]

Location is generally less important than wind direction here, which you aren’t tracking.

Having a few internal and external sensors for various gasses could work, but it’s a surprisingly difficult problem.

[schiffern]

> 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. ;)

To good air and good health! Cheers

[Retric]

Your nose is really really bad chemical sensor because it caress more about novelty than absolute levels.

https://en.wikipedia.org/wiki/Olfactory_fatigue

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.

[sizzle]

I always crack my sunroof an inch and pull the shade forward go get some fresh air in recirculate mode so I’m not picking up crap from the engine bay.

How does the fresh air mode on the car not pull in CO gases from the engine bay? Surely a pleated cabin filter is not enough to stop it? Or does the air come from the manifold air intake?

[bruckie]

There should be very low levels of CO (at least from your car) in the engine bay, since exhaust is vented out the back of the car, and your engine shouldn't be leaking exhaust gases in other places. You might have some CO there from the cars in front of you, though.

[lukevp]

The air intake in the grille is only for the engine’s use. The fresh air intake is not in the engine bay, it’s typically at the base of the windshield.