Hi @Joanna_Louie, the gas sensor measures total VOCs.
The VOC sensor we use is the BME680 from Bosch. You can view Bosch’s website about it at the following link: Gas Sensor BME680 | Bosch Sensortec. That page also includes the sensor’s datasheet.
Currently, the BME680 sensor’s VOC readings are in an experimental phase. We are working on fully understanding the readings and how to implement them into PurpleAir devices properly. You can read more about this at the following link: BME680 VOC Scale Change on the PurpleAir Map.