The BME680 is not selective to some specific gases, but sensitive to the total concentration of VOCs in the envrionment. Since the list of VOCs is so long it would not be relevant to list them all here (there are of example more than 200 VOCs in human breath alone).
The BME680 is typically sensitive to almost all VOCs, with the exception of CO2 and Nitrogen.
In environments where humans are the main source of VOCs (e.g. in a bedroom) though, we provide in our BSEC library a CO2-equivalent output, based on the characterization of the BME680 and correlation with field results.
handytech: "The BME680 is typically sensitive to almost all VOCs, with the exception of CO2 and Nitrogen."
Is this right? interesting (for me... 😉 ) ...
The fresh air contains about 78% nitrogen (N2), 21% oxygen (O2), 0.04% carbon dioxide (CO2), water vapor and various noble gases.
The exhaled air still contains 78% nitrogen (N2), but only about 17% oxygen (O2) and about 4% carbon dioxide (CO2) and about 1% other components such as acetone or hydrogen.
If we want to detect (bad) used air in workrooms or living spaces - how it work if sensor cannot detect CO2? Will be detected the oxygen (O2) difference?
Would be interesting for me to understand it.
And - users of sensor are aware about the fact that the result will be "a CO2-equivalent output" without including the CO2 value itself?
I know that sensor is detecting bad air - maybe you can explain it? 😉
Thanks for any clarification 🙂
(PS: the air values were taken from Wikipedia)
Your values seem correct, but also highlights that the order of magnitude of CO2 and VOC concentrations are quite different.
In a same way, CO2 sensors are VOC sensors are sensitive to their respective orders of magnitude, therefore VOCs can be detected even if they only represent a portion of the remaing 1% in this example.