A colorless gas, formula NH3, with a sharp, irritating odor, having a density about six- tenths that of air at the same temperature and pressure (0. 7720 g cm−3 at STP). A reduced nitrogen gas, NH3 is emitted in large quantities from animal feedstocks, sewerage plants, etc. Ammonia is very soluble in water and is scavenged from the lower atmosphere by clouds. It is the most abundant alkaline gas in the atmosphere and as such plays a large role in neutralizing acidity from sulfuric and nitric acids via formation of the ammonium ion. Large quantities of ammonia gas, and probably even ammonia crystals, occur in the atmospheres of the large planets Saturn and Jupiter. See air.