The Scientific Basis

Footnotes for Chapter 4

1 Atmospheric abundances for trace gases are reported here as the mole fraction (molar mixing ratio) of the gas relative to dry air (ppm = 10-6, ppb = 10-9, ppt = 10-12); whereas the burden is reported as the total mass of that gas in the atmosphere (e.g., Mt = Tg = 1012 g). For most trace gases in this chapter, the burden is based on the total weight of the molecule; for the N-containing gases, it includes only the mass of the N; and for some VOC budgets where noted, it includes only the mass of the C.