Which is better for car ventilation: external air or internal recirculation?
This depends on the circumstances: when in a traffic jam in a tunnel, it is better to let the air circulate internally. In tunnels in Brussels, NO2 concentrations can be more than 10 times that in the Brussels open air. However, when you leave the tunnel or the traffic jam dissolves, don't forget to turn on the external ventilation again. By switching on the internal ventilation for a prolonged time, the air quality inside the car will decrease also.