emissions can be a hot topic in the politics of climate change. Nitrous oxide is also released as a by-product of burning fossil fuel, though the amount released depends on which fuel was used. It is also emitted through the manufacture of nitric acid, which is used in the synthesis of nitrogen fertilizers. The production of adipic acid, a precursor to nylon and other synthetic clothing fibres, also releases nitrous oxide. The total amount of nitrous oxide released that is of human origins is about 40 percent. Ozone layer depletion Nitrous oxide has also been implicated in thinning the ozone layer. A 2009 study suggested that emission was the single most important ozone-depleting emission and it was expected to remain the largest throughout the 21st century. Legality In the United States, possession of nitrous oxide is legal under federal law and is not subject to DEA purview. It is, however, regulated by the Food and Drug Administration under the Food Drug and Cosmetics Act; prosecution is possible under its "misbranding" clauses, prohibiting the sale or distribution of nitrous oxide for the purpose of human consumption. Many states have laws regulating the possession, sale and distribution of nitrous oxide. Such laws usually ban distribution to minors or limit the amount of nitrous oxide that may be sold without special license. For example, in the state of California, possession for recreational use is prohibited and qualifies as a misdemeanor. In August 2015, the Council of the London Borough of Lambeth (UK) banned the use of the drug for recreational purposes, making offenders liable to an on-the-spot fine of up to £1,000. In New Zealand, the Ministry of Health has warned that nitrous oxide is a prescription medicine, and its sale or possession without a prescription is an offense under the Medicines Act. This statement would seemingly prohibit all non-medicinal uses of nitrous oxide, although it is implied that only recreational use will be targeted legally. In India, transfer of nitrous oxide from bulk cylinders to smaller, more transportable E-type, 1,590-litre-capacity tanks is legal when the intended use of the gas is for medical anaesthesia. See also DayCent Fink effect Nitrous oxide fuel blend References External links Occupational Safety and Health Guideline for Nitrous Oxide Paul Crutzen Interview Freeview video of Paul Crutzen Nobel Laureate for his work on decomposition of ozone talking to Harry Kroto Nobel Laureate by the Vega Science Trust.