system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the air at night more 'fresh' than in the day?

title, all I can think of is traffic but me and others have experienced it in multiple cities?
gpt
I think it has to do with a change in temperature.  The air cools, especially relative to a hot day, and feels 'fresher.'

Edit: the drop in temperature will also usually reduce the amount of moisture in the air.  High humidity generally feeling 'thick' or 'heavy'.