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
Underground coal gasification oxidants (air, oxygen) and steam to ignite and fuel the underground combustion process. Separate production wells are used to bring the product gas to the surface. The high pressure combustion is conducted at temperature of , but it may reach up to . The process decomposes coal and generates carbon dioxide (), hydrogen (), carbon monoxide (CO), methane (). In addition, there are small quantities of various contaminants including sulfur oxides (), mono-nitrogen oxides (), and hydrogen sulfide (). As the coal face burns and the immediate area is depleted, the oxidants injected are controlled by the operator. There are