Provides the global average atmospheric composition at present day conditions (year 1998). The mixing ratio is generally defined as the ratio of the mass of an atmospheric constituent to the total mass of dry air. If not otherwise indicated, the term mixing ratio normally refers to water vapor. Here however the mixing ratio is provided for all constituents other than water. The mixing ratio is given as a mole fraction, i.e. the mass of each constituent gas (expressed in moles) divided by the total mass of dry air (also expressed in moles).
character vector selecting the gases whose composition should be provided.
A vector providing the mixing ratio of the selected gases.
Sarmiento JL and Gruber N, 2006. Ocean Biogeochemical Dynamics. Princeton University Press, Princeton. p 85.
They cite Weast and Astle (1982) for all gasses except CO2, CH4 and N2O. For the latter three greenhouse gases, the 1998 concentrations are taken from Ramaswamy et al., 2001. Note that the sum of all mixing ratios is slightly larger than one, presumably due to the use of increased greenhouse gases values as compared to Weast and Astle (1982). In fact, the mixing ratio are changing slightly each year due to increases in greenhouse gas concentrations.
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