The main gas responsible for acid rain is sulfur dioxide (SO2). When released into the atmosphere, primarily from burning fossil fuels such as coal and oil, sulfur dioxide reacts with water vapor, oxygen, and other substances to form sulfuric acid. This acid can then fall to the ground as acid rain, which can have harmful effects on aquatic ecosystems, soil quality, and vegetation. The phenomenon can damage buildings and historical monuments, particularly those made of limestone and marble. Efforts to reduce sulfur emissions, such as regulatory policies and cleaner energy sources, are essential for mitigating acid rain.