The AirGradient air quality monitors AirGradient ONE and AirGradient Open Air contain the Sensirion SGP41 TVOC/NOx sensor module. This is one of the most accurate TVOC module on the market.

The sensor module provides index based sensor measurements but also conversion formulas to convert the index into an absolute measurement suitable for building certifications.

The formula used is:

TVOCIsobutylene [μg/m3] = (ln(501 − 𝑉𝑂𝐶𝐼𝑛𝑑𝑒𝑥) −6.24) ∙ (−878.53)

This result is visible on the AirGradient dashboard as “TVOC (Ind30)” value (and from 7. May 2025 onwards as “TVOC (μg/m3)”).

IMPORTANT: For the correct calculation of this absolute value, the “Normal learning time offset” in the General Settings, Calibration Settings Menu needs to be set to “720”.

For further information please read the Compliance of Sensirion’s VOC Sensors with Building Standards Document.