people out enjoying the cool evening air
Refers to people who go outside on a hot evening to enjoy the cooler air, often in a park, by a river, or on a veranda.
In the evening, more people come out to enjoy the cool air along the river.
People cooling off on the veranda are using round fans.
Compound of 涼み (noun form of verb 涼む 'to cool off') and 客 ('guest, visitor').