Whether the filtration system of private car air conditioning is effective depends on the filtering effect of the cartridge. If there is only one person in the car and the road is open, you can not wear a mask; if more than one person is riding in the car and passing through a crowded place, you need to wear a mask and turn on the internal circulation mode of the car air conditioner. Inside the car is a relatively closed space, after locking the doors and windows, the air can enter the car through the car air conditioning system, and when the air conditioning filter is better, it can effectively isolate the virus. If the cartridge effect is difficult to determine, it is still recommended that owners and passengers wear masks correctly.