Amazing work, and I love how you have a focus on schools. My son's old school was adjacent to a major thoroughfare here in Melbourne, Victoria, and it was the biggest negative with it for me. Only for a year, but I'm hopeful too much damage wasn't done.

Would love a full package sensor like this for our own house (I have three purifiers..) so I'll get in touch once I've learned soldering, which requires acquiring the necessary tools.