What is the difference between internal and external air circulation?

[McNoah]

The differences between internal and external air circulation: 1. Different principles: Internal circulation keeps the air inside the car flowing in a closed environment; External circulation brings outside air into the vehicle. 2. Different air intake locations: Internal circulation draws air from inside the cabin, preventing outside air from entering; External circulation's air intake is located below the front windshield wiper, pulling outside air into the car. 3. Different effects: Prolonged use of internal circulation can make the air stale, reduce oxygen levels, cause discomfort like heat and fatigue, and affect driving safety; External circulation maintains air flow between inside and outside the car, preventing excessive carbon dioxide concentration.