There is a product called a clay bar that will get rid of the contamination on top of your paint. It is available as a kit at any auto parts store for around 17-20 dollars. After you wash your car, don't dry it. Then spray your car with the lubricant that comes with the kit. Then gently glide the clay over the lubricated areas of the car, being sure to keep the car lubed. After you go over the entire car you can polish the car with any polishing compound if you want. This will remove the oxidation on your paint if there is any. The oxidation is what makes your paint dull from sitting in the sun for long periods of time. You will want to wax your car after you do all this because it will be very clean and get dirty very fast if left unprotected. Hope this helps!