MadSci Network: Environment

Re: How much co2 does a human exhale?

Date: Sun Sep 26 21:51:53 2004
Posted By: Steve Mack, Post-doc/Fellow, Molecular and Cell Biology
Area of science: Environment
ID: 1095871322.En

Hi Sopac,

This is an interesting question that is hard to answer accurately. I recently answered a question that was related to this one (1070824959.Bc) so I thought I would take a crack at answering this one.

From the previous answer, you can see that we produce 6 moles of CO2 for every 6 moles of O2 that we consume. In addition, we know that we consume about 300 ml of O2 per minute (310 for the "average" man, and 260 for the "average" woman) resting.

Using the ideal gas law (detailed in the previous answer), we know that the one mole of any gas will take up 22.4 liters of volume at 1 atmosphere of pressure and about 273 Kelvin. This means that the same volume of CO2 (about 300 ml per minute) will be released. In addition, we can calculate the mass of CO2 exhaled per minute. The ideal gas law tells us that a person consumes about 0.012-0.014 moles of O2 per minute. We know that the molecular weight of CO2 is 44.0095 (12.0107 for Carbon + 2*15.9994 for Oxygen), so that they are exhaling between 0.5 and 0.6 grams of CO2 per minute.

Remember that these numbers are for the so-called basal metabolism, and they go up depending on the level of activity, but this should give you a baseline from which to extrapolate. There are 1440 minutes in a day, so that is 0.74 to 0.88 kilograms per person per day, and multiplied by 6 billion (3 billion adult men, and 3 billion adult women), that comes to 4.8 billion kilograms per day.

Now, this is only a rough estimate. The solubilities of O2 and CO2 in the blood are different, so the ratio of inhalaed O2 to exhaled CO2 might not be exactly 1. The average daily oxygen consumption is likely much higher, since most people don't spend the entire 24 hours in a day sitting around resting. Finally, the number 6 billion includes a lot of children, who weren't included in these calculations.

Good luck, I hope this helps!

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