Hi,
My research team and I were attempting to understand the differences between cf1 and atm calibration methods.
We get the same outcomes and are looking for information on the algorithms of the two methods.
Does anyone know where I can find this kind of information?
Thanks.
Hi @ronist, I just answered this question in a response to your email. However, I’ll repeat the information here.
The algorithms used to calculate CF1 and ATM are unknown to us. It is considered proprietary information by Plantower (the OEM of the laser counters we use in our sensors). You can, however, find research from the US EPA on this that may give you further insight. Upon doing a quick search, I found this article that might start you in the right direction: https://www.researchgate.net/figure/Comparison-of-the-24-h-raw-PurpleAir-PA-cf-1-and-cf-atm-PM-25-outputs-a-and-both_fig3_352663348.
@ronist , Plantower’s PMS5003 Chinese language data sheet explains the difference between CF=1 (standard particle) and CF=ATM (atmospheric environment) PM readings. Translated from page 12:
Note: The standard particle mass concentration value refers to the mass concentration value obtained by density conversion using industrial metal particles as equivalent particles, which is suitable for environments such as industrial production workshops. The mass concentration of particulate matter in the atmospheric environment is calculated by using the main pollutants in the air as equivalent particles for density conversion, which is suitable for ordinary indoor and outdoor atmospheric environments.
The module can only detect the sizes of the particles and count how many there are. It doesn’t know how much the particles weigh. So to report mass concentration measurements in μg/m³, it must make an assumption about the average density of the particles. The two different calibration factors each make a different assumption for different kinds of pollutants. CF=ATM is for normal atmospheric pollutants, which for a product designed in China we should imagine is smoke or smog. CF=ATM is probably what you want. CF=1 would be appropriate for metal particle pollution, which is probably not what you want, unless you are taking measurements inside a metal fabrication workshop. The algorithm that Plantower modules use to translate particle counts to mass concentrations is proprietary, and not divulged by the company. We can only guess how that works.
On the PMS5003, CF=1 and CF=ATM readings are the same up to 25 μg/m³, and above that, CF=1 readings are higher than CF=ATM readings.