Acid rain is caused by emissions of sulfur dioxide and nitrogen oxides reacting with water and oxygen in the air to form acids. It falls to Earth as rain, snow, fog or dry particles. It harms plants, aquatic life, and infrastructure. Solutions include reducing emissions through cleaner energy sources and regulating power plants and vehicles. Governments have implemented policies since the 1970s with some success in reducing acid rain-causing emissions, though it remains a problem exacerbated by increasing industrialization.