The universe does strange things in life, and it just happens that one my diagnostic jobs this morning before a long drive up to Doncaster was to check a "malfunctioning " HVAC on year old Austral.
So once the reported problem was sorted, I generated a Air quality sensor fault to see what it says and in the description it had the following, but I have to say this is a new gen vehicle so things may be slightly different but the basics will be the same.
The Toxicity sensor is part of the air conditioning system. It measures pollutants, in the form of oxidisable or reducible gases, in the air outside your car. gases include carbon monoxide, hydrocarbons (vapours from benzene or petrol) and other partially burnt fuel components.
If the quality of the outside air drops, the control system activates the Climatronic air recirculation mode, stopping polluted air from coming in and maintaining the quality of air inside the car.
signal is activated through a change in the impedance of a metal layer triggered by the absorption of reducing (CO) and oxidizing (Nox) gases The measuring range is From 5 to 200 ppm for CO and From 0,1 to 5 ppm for Nox