Weathering release occurs of Ca and other ions into surface waters. Rainfall is acidic because atmospheric carbon dioxide dissolves in the rainwater producing weak carbonic acid. In unpolluted environments, the rainfall pH is around 5.6. Acid rain occurs when gases such as sulfur dioxide and nitrogen oxides are present in the atmosphere. These oxides react in the rain water to produce stronger acids and can lower the pH to 4.5 or even 3.0. Sulfur dioxide, SO, comes from volcanic eruptions or from fossil fuels, can become sulfuric acid within rainwater, which can cause solution weathering to the rocks on which it
Nitrogen halogenating agents. Nitrogen forms nine molecular oxides, some of which were the first gases to be identified: NO (nitrous oxide), NO (nitric oxide), NO (dinitrogen trioxide), NO (nitrogen dioxide), NO (dinitrogen tetroxide), NO (dinitrogen pentoxide), NO (nitrosylazide), and N(NO) (trinitramide). All are thermally unstable towards decomposition to their elements. One other possible oxide that has not yet been synthesised is oxatetrazole (NO), an aromatic ring. Nitrous oxide (NO), better known as laughing gas, is made by thermal decomposition of molten ammonium nitrate at 250 °C. This is a redox reaction and thus nitric oxide and nitrogen are also produced as