The SparkFun SGP40 Air Quality Sensor provides a measurement of the quality of the air in your room or house. The SGP40 is based on Sensirion's CMOSens technology and uses a metal oxide (MOx) sensor with a temperature controlled micro hotplate and provides a humidity-compensated volatile organic compound (VOC) based indoor air quality signal. Both the sensing element and VOC Algorithm feature an unmatched robustness against contaminating gases present in real world applications enabling a unique long term stability as well as low drift and device to device variation.
The SGP40 does not return specific concentrations or VOC gases. Instead, it outputs a digital value based on common VOC gases present in an indoor environment and this value can be combined with Sensirion's VOC Index Algorithm to detect the relative intensity of VOC events in relation to the average readings in a 24hr period.
More information is available on the website of Sparkfun.