Acid rain is etching in the painted surface caused by acid contained within moisture that accumulates on vehicle’s horizontal surfaces. As the water evaporates and is baked into the surface with sunlight, the nitric and sulfuric acid remain and create the damage. When repairing acid rain damage, it is important to select a compound formulated to correct this type of etching. See: Compounds It is also critical to neutralize the acid on the vehicle’s surface before correcting the damage. This is done by using a high ph car wash soap or Neutraseal on the area, and allowing it to dwell for one minute. If the acid isn’t neutralized, the etching will recur.