Trace gas Trace gas The most abundant gases in the atmosphere are nitrogen (78.1%), oxygen (20.9%), and argon (0.934%). Combined, oxygen, argon, and nitrogen make up 99.934% of the gases in the atmosphere (not including water vapor). The other gases that are not part of the 99.934% of the atmosphere are called trace gases. The abundance of a trace gas can range from a few parts per trillion (ppt) by volume to several hundred parts per million by volume (ppmv). When a trace gas is added into the atmosphere, that process is called a "source". There are two possible types of sources
Industrial gas such as vacuum, which is often provided in hospital gas systems; purified compressed air; or refrigeration. Another unusual system is the inert gas generator. Some industrial gas companies may also supply related chemicals, particularly liquids such as bromine and ethylene oxide. Most materials that are gaseous at ambient temperature and pressure are supplied as compressed gas. A gas compressor is used to compress the gas into storage pressure vessels (such as gas canisters, gas cylinders or tube trailers) through piping systems. Gas cylinders are by far the most common gas storage and large numbers are produced at a "cylinder fill"