I tested the results with an insulated box with an open top covered with glad wrap, and confirmed 11 F less than ambient temp at night, at a variety of humidities. I haven't gotten up early ( or stayed up late ) enough to do a test in the early morning when it's close to 100 percent humidity, but it seems to not be affected by atmospheric humidity, which would confirm it's emitting at that "atmospheric window".

The materials are cheap at scale and the process is probably about as complicated as brewing beer, actually probably less so.

I bought a pack of standard asphalt roofing tiles, so I could paint them and leave them exposed and see how quickly dust, rain and etc degraded the effect. I used the acrylic / acetone / water paint that NightHawkInLight describes, but also tried mixing it with clear coat, and I have a few other cheap and scalable application methods to try.