I'd go with one of acrid; pungent; sharp; or bitter.
Most acids don't actually smell of anything. If an acid is strong enough to smell, it will normally be highly unpleasant, as what it'll be doing is dissolving into the liquid in your nose and, well, turning it into the acid you're smelling... and you don't want acid up your nose.
The pov character for that line has a much stronger sense of smell than a human, so he'd pick up on fainter traces. But no, he doesn't like it much at all.
I'd strongly advise against bitter, because bitter is what we taste for bases - compare caffeine (bitter) to lemons (sharp, acrid) and vinegar (acrid, sour). As others have said though, acids smell of themselves, basically, and aside from sour, they'll all be fairly distinctive, especially to someone with a more refined nose.
That said, many common acids are also found in nature, so citric acid has fruity overtones as does malic, hydrochloric acid gives the sharp stink of vomit (in part), prussic acid smells like almonds and so on. Hydrofluoric acid smells like oh-shit-my-bones-are-melting.
He's smelling an acid that doesn't exist in reality, that he doesn't initially recognize as an acid. I'll probably go with either "sour" or "sharp" as the initial descriptor, or both.
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Most acids don't actually smell of anything. If an acid is strong enough to smell, it will normally be highly unpleasant, as what it'll be doing is dissolving into the liquid in your nose and, well, turning it into the acid you're smelling... and you don't want acid up your nose.
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That said, many common acids are also found in nature, so citric acid has fruity overtones as does malic, hydrochloric acid gives the sharp stink of vomit (in part), prussic acid smells like almonds and so on. Hydrofluoric acid smells like oh-shit-my-bones-are-melting.
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