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0 pointsFireBeyond9mo ago0 comments

> A person outputs about 1kg of CO2 per day, which is less than 1 gram per minute.

I'm skeptical about this. Normal adult tidal volume is about 500mg, with a normal respiratory rate of 12/min, so 6L/min. Normal air is about 0.05% CO2, so you're at 3 grams/minute atmospherically that is inspired and expired.

We actually output closer to 4% CO2. 240ml/minute. With the windows and doors closed in my 10x20 living space and 4 people, CO2 can easily go from a baseline 4-500PPM to over 1000 in an hour. That's not 240 grams of CO2 doing that.

https://airly.org/en/the-composition-of-inhaled-and-exhaled-...

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vitus9mo ago

You're mixing your units -- 0.05% of 6L is 3mL. In order for that to weigh 3g, atmospheric CO2 would have to be as dense as water.

Most figures I see peg 1mL of CO2 at closer to 2mg (it's about 50% heavier than the equivalent atmospheric volume, since that's mostly N2 with some O2). Your estimate of 240 mL / minute is about 346L per day, or about 700g of CO2. That's roughly the same order of magnitude as the cited 1 kg / person / day.

edit: Another way of thinking about it: if you scale up your numbers to grams per day, you'd end up with a ludicrous 346 kg / human / day. Multiply that by 12/44 (mass of Carbon-12 vs CO2), and that's the equivalent of a human shedding 100kg of carbon every day from just breathing. Most humans don't even weigh that much.

FireBeyondOP9mo ago

You're absolutely right, I apologize - I did mix units, and my thoughts collapse from there.

gpm9mo ago

For what it's worth here's a NASA document using the same 1kg/day number: https://ntrs.nasa.gov/api/citations/20090029352/downloads/20...

I don't know where I originally got that value from, it's one that has stuck in my head for years.

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