When we exhale, what gasses are present and in what percentages? I know the basic cycle is that we breathe in O2 and exhale CO2. But, we’re also breathing in nitrogen and a bunch of other gasses. So, what exactly are we breathing out?
I had a lung capacity, and oxygen uptake/CO2 release etc. tests run recently. They used a trace gas as a marker. A full answer would require a physiology major to provide the fine details.
The air we breath in is about 21% oxygen and 79% nitrogen by volume (partial pressure) neglecting water vapour. The air we breathe out is about 16% oxygen, 75% nitrogen, 4% CO2 and 5% water vapour by volume.
Note that the 79% nitrogen you breathe in is the same quantity of nitrogen as the 75% you breathe out - it’s just that the volume you breathe out is greater due to added water vapour and increased temperature.
The traces of methane and ammonia reported by Walloon I have no idea about. The 400-800 ppb may be right for CO, it’s way too low for CO2.
Due to the added water vapour, but not due to the increased temperature. Assuming ideal gas behaviour, the volume percentage of nitrogen will not change as you increase the temperature - the specific volume of all the gases in the mixture will increase in the same degree.
If you compare like with like (dry gas in, dry gas out), and assume that each molecule of CO[sub]2[/sub] replaces a molecule of O[sub]2[/sub], you should find the volume percentage of nitrogen in exhaled gas is the same as in air.