system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes the winter air smell so nice and fresh?

Whenever I open the window on a day with zero/negative C°, I'm hit with this unmistakable smell of winter. But there isn't anything to give off the smell, only cold air and snow.
gpt
Maybe the "clean air" is just air without natural contaminants like pollen and animal pheromones.  It could also be the physical feeling of your turbinate bones warming and humidifying the air entering your nose.