Common in official signage, regulations, and hospitality listings. 'Smoke-free' implies the air is actually free of smoke, whereas 'non-smoking' merely states that smoking is not permitted.
常見錯誤
We sat in a free-smoke area.
We sat in a smoke-free area.
The word is 'smoke-free' (the thing banned + 'free'), not 'free-smoke'.
This is a no-smoking zone' (when describing the clean-air outcome).
This is a smoke-free zone.
'Non-smoking' or 'no-smoking' focuses on the rule; 'smoke-free' focuses on the result (clean air).