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On extended bicycle trips I sometimes slept under a plastic sheet, which helped with mosquitoes on hot nights. But there was a noticeable build-up of ammonia which made this almost impossible for more than an hour or so at a time.

Air is mostly nitrogen $(N_2)$ and there is always water (containing hydrogen) on a humid day. But I wonder about the mechanism for the formation of ammonia under these circumstances? There are (according to Wiki) trace amounts of methane and $H_2$ in the air. But methane and hydrogen (g) are I think pretty stable.

I wonder if the presence of exhaled air (containing $CO_2)$ could be a factor?

Thanks for any ideas.

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up vote 5 down vote accepted

If you're absolutely sure it's Ammonia ($NH_3$) you're smelling, it's probably from you.

Ammonia will not spontaneously form at any significant rate from the air. Molecular Nitrogen ($N_2$) is extremely stable.

What can happen is that during marathon-type activities, muscles turn from carbohydrates (which are later converted into glucose and enter into the Krebs Cycle) as an energy source to proteins themselves.

One of the waste products of protein catabolism is Ammonia, which is excreted in your sweat if the body can't convert it into Urea ($CH_4N_2O$) quickly enough:

Ammonia forms with the oxidation of amino groups (-NH2), which are removed from the proteins when they convert into carbohydrates. It is a very toxic substance and only one nitrogen atom is removed with it. A lot of water is needed for the ammonia excretion.

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Yes, no mistake about the ammonia. This makes perfect sense. Long distance cycling with little to eat, intense humidity and heat. Thanks. –  daniel Mar 3 '13 at 22:06
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