Final answer:
Keeping the car cool, rather than warm, helps the inside of the windows stay clean longer by reducing humidity and condensation inside the car.
Step-by-step explanation:
To keep the inside of car windows clean longer, the most effective action is to avoid keeping the car warm. When the interior of a car is warm, especially if there are passengers, humidity increases, and this can turn into condensation on the windows when the car cools down. In addition, the presence of passengers can introduce more pollutants, skin cells, and oils into the car's atmosphere, which can all contribute to the windows getting dirty.
Ventilating the car is an excellent way to reduce pollutants and moisture. Increasing the ventilation in a car often involves opening windows slightly or using car vents and air conditioning with the vent control open, especially when parked. This approach minimizes condensation and buildup of dirt or other substances on the windows's interior surfaces.
On warm, sunny days, car windows trap sunlight and heat up the car's interior, which also causes an increase in humidity inside when people are present. Keeping the car cooler by seeking shade or using sun control methods like window tints or sunshades can decrease the inside temperature, thus reducing the risk of condensation and keeping the windows cleaner for a more extended period.