Acid rain is an environmental problem caused by air pollution from vehicles and factories that burn fossil fuels. Compounds present in the air pollution can interact with molecules in our clouds and drop the pH level of our rain to dangerously low levels. Acid rain is an environmental problem because it can change the pH of soil and water. Some species are not suited for acidic conditions, and biodiversity can be lost. The source of the air pollution can affect ecosystems hundreds of miles away! This is because wind and weather can travel great distances. Forests that are hundreds of miles away from industrial areas have been impacted by acid rain.