We generally see the following sized particles discussed the most by air quality initiatives, and companies which make air quality monitors: 10µm, and 2.5µm.
Why is this the case, when the scientific material all talks about particulate matter SMALLER than 2.5µm being harmful for you?
My outdoor air quality sensor shows the following: https://imgur.com/a/jcwNXvr
As you can see, the the 0.3µm, 0.5µm, and 1.0µm readings are quite high, even though the main indicator is showing the air quality as being “clean,” on the basis of the PM2.5 readings.