Kyoto Protocol European Union-15, made up of 15 states at the time of the Kyoto negotiations) commit themselves to binding targets for GHG emissions. The targets apply to the four greenhouse gases carbon dioxide (), methane (), nitrous oxide (), sulphur hexafluoride (), and two groups of gases, hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs). The six GHG are translated into CO equivalents in determining reductions in emissions. These reduction targets are in addition to the industrial gases, chlorofluorocarbons, or CFCs, which are dealt with under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. Under the Protocol, only the Annex I
Nitrous oxide dominant. In a vacuum thruster, this may provide a monopropellant specific impulse ("I") of as much as 180 s. While noticeably less than the "I" available from hydrazine thrusters (monopropellant or bipropellant with dinitrogen tetroxide), the decreased toxicity makes nitrous oxide an option worth investigating. Nitrous oxide is said to deflagrate at approximately at a pressure of 309 psi (21 atmospheres). At 600 for example, the required ignition energy is only 6 joules, whereas at 130 psi a 2500-joule ignition energy input is insufficient. In vehicle racing, nitrous oxide (often referred to as just "nitrous") allows the engine to burn