The air quality is calculated by using BSEC software from Bosch.

Dr. Fix, Bosch Sensortec(full interview), says: "VOC sensors can detect almost all organic contaminants in indoor air. That is why they are called air quality sensors. We want to breathe in fresh, clean air, so essentially nitrogen, oxygen and a reasonable amount of moisture. Anything else in the air is usually a contaminant. CO₂ sensors only detect CO₂ and nothing else. The measurement of CO₂ in room air goes back to Prof. Max Pettenkofer, who in 1858 coined the guideline value of 1000 ppm CO₂. From a chemical point of view, however, CO2 itself is a fairly non-reactive gas, that has hardly any effect on our well-being. On the International Space Station (where you can’t open windows ;-)) the CO₂ value is regulated to 5000 ppm. Extensive studies by NASA show that this is sufficient and that it is especially important to filter out all other impurities from the room air. Human exhaled air is reliably detected by VOC and CO₂ sensors. A VOC sensor may require ventilation a little earlier or more often since it also detects numerous other impurities. We consider this to be sensible."

Our BME688 Breakout Board uses 3.3V logic levels - for a 5 V logic level device such as the Arduino Uno, you would need to use an I2C level shifter.