Edit: I misread that you're showing light pollution, not air pollution, so disregard my comments. But maybe an idea for another site?

Very cool. I was buying some land a few months ago, and made a similar map of the country to help choose areas with consistently good air quality.

I couldn't get the calendar to change from October, so I couldn't check myself, but I was wondering if you adjust for seasonality. Some areas have a distinct "burning season" when farmers burn their fields and the air quality is significantly worse.

I was also wondering if you're using publicly available sensor data. The granularity looks a lot better than what I had downloaded.