Green’s Dictionary of Slang

lit. or fig., atmosphere or ambience, used neg. or pos.

1998		K. Sampson Awaydays 81: It’s an oldish crew and there’s quite a good atmos on the train.
2005		P. Howard Curious Incident of the Dog in the Nightdress 239: It’s a pretty bad atmos.
2021		P Howard Braywatch 24: I pick up on as definite atmos.
2024		J. Meades Empty Wigs (t/s) 103: The autumnal atmos is dense with fungal particulates.