Nitrous oxide (dinitrogen oxide or dinitrogen monoxide), commonly known as laughing gas, nitrous, or nos, is a chemical compound, an oxide of nitrogen with the formula . At room temperature, it is a colourless non-flammable gas, and has a slightly sweet scent and taste. At elevated temperatures, nitrous oxide is a powerful oxidiser similar to molecular oxygen. Nitrous oxide has significant medical uses, especially in surgery and dentistry, for its anaesthetic and pain-reducing effects. Its colloquial name, "laughing gas", coined by Humphry Davy, is due to the euphoric effects upon inhaling it, a property that has led to its recreational use as a dissociative anaesthetic. It is on the World Health Organization's List of Essential Medicines. It is also used as an oxidiser in rocket propellants, and in motor racing to increase the power output of engines. Nitrous oxide's atmospheric concentration reached 333 parts per billion (ppb) in 2020, increasing at a rate of about 1 ppb annually. It is a major scavenger of stratospheric ozone, with an impact comparable to that of CFCs. Global accounting of sources and sinks over the decade ending 2016 indicates that about 40% of the average 17 TgN/yr (teragrams, or million metric tons, of nitrogen per year) of emissions originated from human activity, and shows that emissions growth chiefly came from expanding agriculture and industry sources within emerging economies. Being the third most important long-lived greenhouse gas, nitrous oxide also substantially contributes to global warming. Nitrous oxide is used as a propellant, and has a variety of applications from rocketry to making whipped cream. It is used as a recreational drug for its potential to induce a brief "high"; most recreational users are unaware of its neurotoxicity and potential to cause neurological damage. Uses Rocket motors Nitrous oxide may be used as an oxidiser in a rocket motor. It has advantages over other oxidisers in that it is much less toxic, and because of its stability at room temperature it is also easier to store and relatively safe to carry on a flight. As a secondary benefit, it may be decomposed readily to form breathing air. Its high density and low storage pressure (when maintained at low temperature) enable it to be highly competitive with stored high-pressure gas systems. In a 1914 patent, American rocket pioneer Robert Goddard suggested nitrous oxide and gasoline as possible propellants for a liquid-fuelled rocket. Nitrous oxide has been