The Camp fire has had a big effect on the Air Quality Index (AQI) in the Bay Area over the past week or so. AQI is typically measured as an entry in one of 7 bands:
To compute the AQI (typically cited from the PM2.5 #) a formula is used. See the wiki page above.
The PM2.5# is in µg/m3 fortunately there is a Chinese sensor, the PMS7003 that can provide PM1, PM2.5 and PM10 in those units:
So we have a sensor, we already have a Bluepill running Ada with an SPI screen to display the results.
The sensor is a $20 eBay purchase. Bluepills are < $2 as documented on this blog, screen is a little over $3. So for $25 or so you can build your own AQI meter.
Code is in: