The air purifier site is one of four sites where Hornwright Industrial set up the air purifiers - in reality modified to act as tools for converting aerosolized minerals back into solid form.
Found northwest of the town of Lewisburg, this air purifier site has a small stone building with a large toolbox and a duffle bag outside next to a ruined car. Inside, there are more containers to be looted alongside a tinker's workbench and some junk items on the metal shelves. Following the road southeast leads to the air purifier itself, which has more containers and various alcoholic drinks within the fenced area.
Hornwright air purifier site #02 appears only in Fallout 76.