Interesting. Have you found differences in CO2 levels? And if so, what were the worst places for high CO2 and how big were the differences?
Oh yes, it can vary quite a lot. Fresh outside air tends to be a touch over 400 parts per million. Besides virus risk, people start to notice poor air quality and feel more tired above about 1,000 ppm, and other side effects such as headaches can start around 2,000 ppm. Human cognition also suffers measurable deficits at these higher levels.
Someone I follow on Twitter whose risk tolerance seems to be quite a lot lower than mine, and who has done quite a bit of research into the topic, uses the following scale:
<600 ppm: will happily go without a mask.
600-800 ppm: will likely go without a mask, but will be less happy about it.
>800 ppm: will likely wear a mask.
I've been keeping that standard in mind. I will sometimes go maskless at these higher levels, but I'll be mindful that the situation is a bit more risky and will consider limiting my exposure when convenient.
My home office is in my basement and tends to be in the 500-700 range. No particular effort is made to ventilate this area, but it's a pretty large space and the doors to the garage and the outside aren't terribly well sealed. The result seems to be that the CO2 dissipates almost as fast as I exhale it during the day, and by the time I come down the next morning it's pretty close to outdoor levels again.
I spent a weekend with some friends at their family's cabin in the mountains a couple weekends ago. That place is very well-sealed to keep heat in during the winter, but the result is that the CO2 levels climbed quite fast if we kept the windows closed: we're talking levels approaching 2,000 ppm with ten people in the place. One friend, the son-in-law of the cabin's owner, said "so that's why I always feel so sleepy when I come here." That was incidentally where my wife caught COVID. She and I were going without a mask there because there were just three families there, all of whom tend to be on the more cautious side where COVID is concerned, so we decided to let our guard down. Unfortunately one of the families there had visited with their relatives the week before, and found out while we were at the cabin that one of them had tested positive. Once they got home they started experiencing symptoms. We made our kids keep wearing masks inside the cabin because they had a cold, but they avoided the COVID! I avoided it probably because I got the new booster a week before. My wife had a vaccine appointment scheduled for the next week and she got sick. Poor timing!
The curling club I belong to unfortunately has pretty high levels of CO2. They have the HVAC system tuned pretty well to optimize the ice conditions, but the CO2 levels can easily climb above 1,000 PPM if the arena has been full of people curling for a few hours.
I'm currently in the Seattle airport. The air quality here is mostly quite good given how crowded it is! I had some time to kill before my flight (and it was delayed for an hour so I have a bit more time to type this). I spent some time in the south satellite terminal where many of the international airlines operate out of. That one tends to be a bit less crowded and has CO2 levels in the 600-700 range. I then went over to the north satellite terminal (noticeably busier) and the CO2 levels were closer to 900. I'm currently sipping a glass of wine in the Priority Pass lounge in the main terminal and the meter reads 705 ppm. Not bad. The train between the terminals, on the other hand, got up to around 1,500 when it was crowded. Pretty high, but it's also for a short period of time. I'm interested to see what the air looks like on the flight.
Seattlecyclone, Could you provide a link for purchasing your portable CO2 monitor, or is it something related to your work?
I bought
this monitor. It's not cheap, but the Twitter person I mentioned above, and several other folks who are vocally in support of continued vigilance around COVID (and have done way more research into the topic than I) seem to use this one. There are apparently a bunch of cheaper monitors that don't perform very well in validation tests, but this one is the real deal.
