I mean, they're not shoving the link in your face, but I had no trouble finding it. If I'm someone who wants to build one, clicking "build instructions" seems like an obvious place to start.

From there, I can choose which one I want to build, and click "build instructions" on that.

Skimming down the page, the "AirGradient DIY PRO" had a section on making your own PCB that links to the files you need.

On the "AirGradient Open Air Outdoor", they had a link to "technical documentation" which mentioned that it had the schematics and KiCAD files, and it does appear to have those things.

I'm surprised they don't appear to have these files on a GitHub repo somewhere, but they certainly seem to provide the files needed to make your own, and the website says these files are licensed CC-BY-SA.

It is linked on the technical documentation [1].

[1] https://www.airgradient.com/open-airgradient/instructions/di...

I bought one recently (it’s great) and found the source here https://github.com/airgradienthq/arduino