Hi @Guilherme,
This is a great point, and it could be a significant issue. I’ve honestly not considered it much, as I’m almost always near sea level.
AirGradient does not have a similar compensation for altitude, and I’m not sure if SenseAir implements this by default. Here is the information I was able to find. There is no need to read all of the links, but I wanted to include them in case you or any other readers want to dig deeper.
The Sunrise and Sunlight sensors do have this compensation by default (I’m not sure if Aranet changed this at all or just used the default implementation): https://rmtplusstoragesenseair.blob.core.windows.net/docs/Market/publicerat/TDE7318.pdf (page 15)
S8 has similarly impacted by pressure differences (also 1.6% per kPa): https://www.driesen-kern.de/downloads/modul_senseair_s8_004_0_0017_co2sensor_s80050.pdf
Other sensors like the Sensirion SCD30 (https://sensirion.com/media/documents/D7CEEF4A/6165372F/Sensirion_CO2_Sensors_SCD30_Interface_Description.pdf) and the SCD4x sensors appear to have this compensation too: Sensirion SCD41 and SCD40 CO2 Sensors - eMariete
Unfortunately, I can’t find anything on the S8 (used in the AirGradient monitors). SenseAir knows of this issue, as it’s implemented compensations on the Sunrise and Sunlight sensor, and the competition from Sensirion has it, so I wouldn’t be surprised if the S8 also has it. Still, I can’t find anything to confirm this.
All of my comparisons are carried out at low altitudes as I am normally not more than a kilometre from the ocean! I may have to start testing different pressures now, too.
You could add a barometric pressure sensor to an AirGradient monitor (I know there are a few forum posts out there from people who have), but it wouldn’t automatically compensate unless you were really comfortable modifying the device. Therefore, unless we can confirm that the S8 has such compensations, you might want to look at a device with a Sensirion or Sunrise CO2 sensor instead.