<P> Atmospheric concentrations of greenhouse gases are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound). The proportion of an emission remaining in the atmosphere after a specified time is the "airborne fraction" (AF). The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions . As of 2006 the annual airborne fraction for CO was about 0.45 . The annual airborne fraction increased at a rate of 0.25 ± 0.21% per year over the period 1959--2006 . </P> <P> The major atmospheric constituents, nitrogen (N 2), oxygen (O 2), and argon (Ar), are not greenhouse gases because molecules containing two atoms of the same element such as N 2 and O 2 and monatomic molecules such as argon (Ar) have no net change in the distribution of their electrical charges when they vibrate . Hence they are almost totally unaffected by infrared radiation . Although molecules containing two atoms of different elements such as carbon monoxide (CO) or hydrogen chloride (HCl) absorb infrared radiation, these molecules are short - lived in the atmosphere owing to their reactivity and solubility . Therefore, they do not contribute significantly to the greenhouse effect and often are omitted when discussing greenhouse gases . </P> <P> Some gases have indirect radiative effects (whether or not they are greenhouse gases themselves). This happens in two main ways . One way is that when they break down in the atmosphere they produce another greenhouse gas . For example, methane and carbon monoxide (CO) are oxidized to give carbon dioxide (and methane oxidation also produces water vapor, as discussed later). Oxidation of CO to CO directly produces an unambiguous increase in radiative forcing although the reason is subtle . The peak of the thermal IR emission from Earth's surface is very close to a strong vibrational absorption band of CO (15 microns, or 667 cm). On the other hand, the single CO vibrational band only absorbs IR at much shorter wavelengths (4.7 microns, or 2145 cm), where the emission of radiant energy from Earth's surface is at least a factor of ten lower . Oxidation of methane to CO, which requires reactions with the OH radical, produces an instantaneous reduction in radiative absorption and emission since CO is a weaker greenhouse gas than methane, although CO has a longer lifetime . As described below this is not the whole story, since the oxidations of CO and CH 4 are intertwined by both consuming OH radicals . In any case, the calculation of the total radiative effect needs to include both the direct and indirect forcing . </P> <P> A second type of indirect effect happens when chemical reactions in the atmosphere involving these gases change the concentrations of greenhouse gases . For example, the destruction of non-methane volatile organic compounds (NMVOCs) in the atmosphere can produce ozone . The size of the indirect effect can depend strongly on where and when the gas is emitted . </P>

Which of the following contribute(s) to the greenhouse effect in the atmosphere