Acidic oxide Some non-metal oxides, such as nitrous oxide (NO) and carbon monoxide (CO), do not display any acid/base characteristics. Acidic oxides can also react with basic oxides to produce salts of oxoanions: Acidic oxides are environmentally relevant. Sulfur and nitrogen oxides are considered air pollutants as they react with atmospheric water vapour to produce acid rain. Although it is difficult to classify these oxides as acids, the property is manifest in reactions with bases. For example, carbon dioxide reacts with alkali. For this reason, alkali is kept in stoppered vessels to inhibit reaction with atmospheric carbon dioxide. In geochemistry complex silicates
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