Tracer gas measurements are used to calculate the air flow rate in a system. For this purpose, a defined amount of a readily measurable gas is introduced into the system, e.g. via the HVAC unit. The tracer gas is continuously diluted with fresh air so that the air flow rate and air exchange rate can be derived from measuring the concentration of the tracer gas over time.

This method is ideally suitable for air inlets that are difficult to access, as it requires no adapter which could impede air flow.

The special advantage of this method is that it can also be used to assess the influence of wind flow on the fresh air rate inside the vehicle. This is done by carrying out comparative measurements both at standstill and at simulated maximum speed.