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
Gas venting or controlled combustion of gases from coal mining and of so-called biogases. In practice, it is impossible or impractical to capture and filter the air from coal mining (esp open-cast) and to completely degas hydrocarbon product and/or water produced from the ground which in some cases may be disposed at surface for and used after treatment. Melting of methane hydrates in the world's oceans or sea ice would also constitute uncontrolled gas leakage to atmosphere. Gas venting Gas venting is the intentional safe release, without combustion, into the earth's atmosphere of gases that cannot be readily recycled into a production