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
Jacchia Reference Atmosphere Jacchia Reference Atmosphere The Jacchia Reference Atmosphere is a reference atmospheric model that defines values for atmospheric temperature, density, pressure and other properties at altitudes from 90 to 2500 km. Unlike the more common US Standard Atmosphere and related models, the Jacchia model includes latitudinal, seasonal, geomagnetic, and solar effects, but must be supplemented with another model at lower altitudes. The model, first published in 1970 and updated in 1971 and 1977, is based on spacecraft drag data, and is primarily used in spacecraft modeling and related fields. A common assumption while using the Jacchia Model is that the atmosphere