Bonjour James,
When referring to music, i.e. 'popular tune', you can use the expression 'un air populaire' -> plural = 'les airs populaires'.
When referring to 'the air' / 'the sky', you can use 'les airs' (plural form) as per the expression 'par les airs' = 'by air / through the air'. It sounds far better than 'dans l'air'. See link here: cnrtl.fr/definition/airs
I hope this is helpful.
Bonne journée !
Interesting question. Unfortunately my best French reference isn’t here at the moment. Dommage !
The best I can come up with at the moment is that it seems “en l’air” is used to indicate something is in the air, but “dans les airs” and “pars les airs” when describing movement (generally or more travel-related respectively) rather than just position. However, there seem to be all sorts of combinations in use if the less reliable sources are regarded as well.
French native needed to help on usage here.
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