Do you think a car-free day in the world is an effective way to reduce air pollution? It is not worthless. If you imagine a day without car in whole word, you can see that it's affect on many sides that related to air pollution. For instance, there is no car to emision carbon dioxcide in the air, and it's the most obvious example of its affect. Besides, you'll encourage people to do this as many times as thay can by showing them the benefits. On the other hand, if you think about it deeply, you could realize that it's not an effective way from a long term point of view. Although it has a small effective on air pollution, but if you want a sustainable and long term viewpoint you must think for a comprehensive and effective method to reduce air pollution, such as effective ways to encourage people to use public transportations, bicycle, or so on. In conclusion, although a day without car has a positive effect on air pollution, but it is provisional, and it hasn't long term affect on having a blue sky and healthy air.