Air Quality

[Sineos]

The spec should also contain:

• HCHO (Formaldehyde): Although a subclass of the TVOCs, this is one of the most important poisons in living areas and in fact some sensors are able to distinguish between generic TVOCs and HCHO
• PMx: Many of the particle sensors distinguish between PM0.5, PM1.0, PM2.5, PM4.0, PM10 whereas calibration is typically only done against the defined PM2.5 value

[andycarle]

Thank you for the recommendations! We'll take a look at incorporating these into an upcoming revision to the spec.

[Sineos]

One additional comment to https://github.com/EcmaTC53/spec/blob/master/docs/proposals/Sensor%20Classes%202022.md

Most of the commonly available (read affordable) gas sensors are not able to differentiate between different Alkanes, e.g. LPG, I-butane, Propane, Methane, alcohol etc. Maybe a "combustible gas" class or similar would fit well

[phoddie]

Interesting. If you could provide part numbers and/or links to some gas sensors that fit into your common/available/affordable group, that would be helpful.

[Sineos]

Some example are the MQ-x sensors for which many different variation exists with different sensitivities to various gases.

MQ-2

https://components101.com/sites/default/files/component_datasheet/MQ2%20Gas%20sensor.pdf

MQ-135

https://www.electronicoscaldas.com/datasheet/MQ-135_Hanwei.pdf

Or some other sensor manufacturers:

WSP2110

https://www.winsen-sensor.com/d/files/wsp2110-(ver1_5)---manual(1).pdf

MiCS-6814

https://www.sgxsensortech.com/content/uploads/2015/02/1143_Datasheet-MiCS-6814-rev-8.pdf

As you can see, some gases could be identified by very careful calibration to certain resistance ranges (something probably quite impossible without very specialized equipment). Other will not work at all, since their sensitive curves intersect or are very close nearby.

Edit: While it makes sense to have dedicated classes for individual gases, e.g. H2 or O2 can be identified pretty clearly with the right sensors (e.g. ME2-O2-Ф20 Oxygen Sensor), I dare say that many (most?) are not selective enough to identify individual gases. IMO calling such a sensor a Methane gas sensor, is not really correct.