Nitrous oxide (or dinitrogen oxide) is a colorless gas that consists of two nitrogen atoms and one oxygen atom (N2O). It has a slightly sweet odor and is a mild anesthetic, also known as “laughing gas.” It is solid at temperatures below –91ºC and becomes a gas at −88ºC. N2O is about 50% more dense than air and is highly soluble and stable. N2O slowly breaks down through photochemical dissociation in the stratosphere (reacting with ozone in the presence of sunlight) to free nitrogen (N2) and oxygen (O2) gas.