Vehicle air intakes capture some of the exhaust emissions. Nitrogen dioxide and fine particles emitted by engine combustion enter the car. And they stay there unless the car is regularly ventilated. The more pollutants the vehicle in front of me emits, the more polluted my cabin will be.

In an enclosed space (tunnel, underground parking lot, etc.), in a traffic jam, or behind a polluting vehicle, it’s best to close the windows and turn off the outside air supply. Outside of these circumstances, it’s best to ventilate your vehicle to refresh the air.

Tobacco smoke contains thousands of constituents, some of which are potentially toxic. The particles released can persist even if you smoke with the windows open. They become embedded in the vehicle and are re-emitted by the surfaces of the passenger compartment for days or even months.