Periodically, I notice a layer of residue on my car's finish. Is it from the atmosphere, and is it harmful?
What you are referring to are block particles that come from areas of heavy traffic. They are gritty, abrasive substances coming off tires as they wear. Also, chemicals from diesel smoke and other emissions in the atmosphere settle on your car's surface. If this residue isn't removed immediately, permanent damage to the finish can result.