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The atmospheric content in chemicals is given in concentration (number density),
volume mixing ratio, density or mass mixing ratio.
– For water, other expressions are used as well (see below). –
For neutral molecules, the most commonly used quantity is the volume mixing
ratio, although some species contents are expressed via other variables
(for example, the carbon content is determined by its density).
The content in ions is given as a density.
In addition to the ways listed above, the water vapour amount can also be expressed as relative humidity (RH). Note that the water vapour mass mixing ratio refers to a unit mass of dry air. The mass of water vapour per unit mass of moist air is called specific humidity. Some experiments involved the release and monitoring of tracers. In such cases, the release rate of the species is also given. |