What would Pandora’s atmosphere (Avatar) smell like?

Earth’s atmosphere is mostly made of nitrogen and oxygen, 78% and 21% respectively, with the remaining percentage divided among Argon, traces of other noble gases and carbon dioxide.

The composition of Pandora’s atmosphere is: nitrogen (50%), oxygen (25%), carbon dioxide (18%), xenon (5.5%), hydrogen sulphide (1%), methane and ammonia (0.5%).

A very different mixture compared to the Earth’s atmosphere, and also 20% denser, due to the high percentage of xenon, a heavy and inert gas.

Nitrogen is an odorless gas, as are oxygen, carbon dioxide, xenon and methane, so the smell of Pandora’s air would be entirely determined by that of ammonia (strong and pungent) and of hydrogen sulfide (similar to rotten eggs).

However, ammonia represents less than 0.5%, and may not be detectable, or in any case be less noticeable than the hydrogen sulphide that makes up 1% of Pandora’s air.

It is plausible that a breath of Pandora’s air wouldn’t smell too differently from earth’s air, except for a faint scent of rotten eggs and perhaps an even milder scent of bleach.

The real problem though, would not be the smell of these substances, however unpleasant, but the effect they would have on the body of a human who inhales them.