If you live in an area of heavy smog and pollution, acid rain is something that you are probably well acquainted with. Just as much as acid rain can damage the earth, it can also damage your vehicle's paint over time. Once this type of rainwater gets on your vehicle, the acid concentrates itself on the paint as it dries. It is then reactivated every time the vehicle becomes wet, causing only further damage.
In areas of high pollution, it is best to keep your vehicle out of the elements as much as possible. This is one time when a dirty vehicle is actually better off just staying that way. If you live in an area of high pollution, take your vehicle to the nearest eco-friendly car wash whenever it needs cleaned. If you are practical with your car washing schedule, you can minimize water usage, while also maximizing the life of your vehicle's paint.