Acid rain Acid rain Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals and infrastructure. Acid rain is caused by emissions of sulphur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids. Some governments have made efforts since the 1970s to reduce the release of sulphur dioxide and nitrogen oxide into the atmosphere with positive results. Nitrogen oxides can also be produced naturally by lightning strikes, and sulphur dioxide
21st-century fossil fuel regulations in the United States are subject to New Source Review (NSR) and Prevention of Significant Deterioration (PSD). Emissions from these plants have the largest contributions of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. Facilities in the electric sector are restricted to emission standards defined by the Clean Air Act (United States). While monitoring and controlling environmental releases of plants has been difficult, the EPA has been enforcing their policies regarding air quality over the last decade under President Barack Obama. While the Clean Air Act postulates regulations and rules limiting the emissions of greenhouse gases, other laws are concerned with standards