Another thing to consider is the acidity in pollution, as well as the alkalinity or acidity in the local dirt, depending on where you live. I had the paint on an Integra I used to own ruined by a couple weeks worth of local dust and pollution settling on the car, then a passing shower came by just enough to wet the finish, concentrating the dirt and pollutants in the drops. The sun popped out soon after and baked the drops dry. End result was pits permanently eaten into the surface of the paint.

Something to consider when leaving your car outside.
TrailDust