For those prices, buy an Ambient Weather base station along with this CO2 sensor:

https://ambientweather.com/indoor-wireless-air-quality-monit...

We have low-voc foam in the attic, which outgasses voc’s slowly and constantly. (They measure voc release at application time, not over the product lifetime).

I started actively venting the attic a two months ago. The whole house reeked of foam for a week or so whenever the windows were closed.

It’s fallen off a lot, even though the attic foam is 5 years old.

I think the sponge analogy is correct. If the house is sealed, the VOCs accumulate in the atmosphere, and are reabsorbed into the foam at the rate they are released into the air.

If you leave the house completely open, the outgassing will not be offset by reabsorption.

I think the CO2 in our place accumulates faster than the VOCs I can smell, so opening the windows when the meter tells us to keeps the net rate of outgassing high, and the indoor pollution low. It seems like the outgassing is slowing down now.

I really should get some VOC meters.