Quote Originally Posted by Scott Winners View Post
Using the Bill Penz (Dylos)/100 = PM in mcg/m3 I don't have good agreement. The two meters I have do agree pretty well between PM 2.5 @2.0 to 7.0 mcg/m3, otherwise the Dylos reads higher than the Plantower below 2.0 mcg/m3 and the plantower reads about double the Dylos above 7.0 mcg/m3. Given Bill was looking at wood dust and I am looking at wood smoke I am OK with a different conversion.

(Plantower) x 2.8 = Dylos +/- 30% fits my data even worse.
Keep in mind that the PM2.5 calculation from Dylos particle counts is only a rough approximation. It's based on an "average" particle size of 1.5 micron and an assumed particle mass density of 1.3 g/ml. With only two channels of size resolution you're trying to estimate an average particle mass out of a 125:1 range (mass varies with the cube of dimension). The Plantower sensor has four channels, including a 0.3 micron count, and uses a proprietary algorithm empirically tuned to industrial pollution in China to estimate PM numbers. I would expect the Plantower PM2.5 reading to have better agreement with your official monitoring station than the Dylos calculation.

Plantower x 2.8 / Dylos applies ONLY to 0.5 and 2.5 COUNTS, not PM values.

Also, neither the Dylos nor the Plantower are show raw counts. Those numbers are scaled from the actual analog pulse counts. At very low counts don't expect much correlation. There's a lot of noise in those numbers.