Oxygen atmospheric mixing ratio

Fig. 8. Vertical distribution of molecular oxygen (Oj) mixing ratio in prebiological paleo-atmosphere. Calculations for molecular hydrogen (Hj) = 17 ppmv, carbon dioxide (CO2) = 280 ppmv, and three different solar ultraviolet fluxes.

The rate of the atmospheric chemical transformation of elemental mercury with a given oxidant is dependent on two factors. The first factor is the reactivity of mercury towards a given oxidant at environmentally relevant conditions, such as temperature, pressure, oxygen concentration, and relative humidity. The second factor is the concentration (or mixing ratio) of the oxidant. The existing laboratory studies of mercury kinetic reactions have been obtained using steady state reaction... 

In the middle atmosphere, molecular nitrogen is particularly stable since it cannot be photodissociated below the mesopause. On the other hand, the photodissociation of molecular oxygen can occur at altitudes as low as 20 km. Where transport processes can replace the photodissociated molecules, their abundances remain constant, but as photodissociation rates increase at higher altitudes, mixing ratios begin to decline. Oxygen photolysis initiates a series of reactions which determine the chemistry of the oxygen atmosphere these will be the subject of the next section. 

The chemical loss of 02(1Ag) produces a ground state oxygen molecule. Since 02 is a permanent gas always present at a constant mixing ratio in the middle atmosphere, this process is not photochemically important. Further, the lifetime of 02(xAg) is never more than its radiative lifetime of about an hour, so that photochemical steady state (see Eqs. (2.37) and (5.27)) may be assumed for this species ... 

If, on the other hand, [NO2]0 = [O3]0 = O.thcn [Oj] = 0. This is clear since in the absence of N02 there is no means to produce atomic oxygen and therefore ozone. Thus the maximum steady-state ozone concentration would be achieved with an initial charge of pure NO2- The mixing ratios of ozone attained in urban and regional atmospheres are often greater than those in the sample calculation. Since most of the NO emitted is in the form of NO and not N02, the concentration of ozone reached, if governed solely by reactions 1-3, cannot account for the actual observed concentrations. It must be concluded that reactions other than 1-3 are important in tropospheric air in which relatively high ozone concentrations occur,... 

Variations in atmospheric oxygen have provided unique insight into carbon sources and sinks. Between 1990 and 1997, the mixing ratio of atmospheric O2 decreased by 25 ppmv, when that of atmospheric CO2 increased by 9 ppmv. The decrease in O2 is less than expected from fossil fuel combustion, which has an 02 C02 ratio of 1.43 0.02. As air-sea exchange of CO2 has little impact on atmospheric oxygen, and net land uptake has a O2 CO2... 

In order to control the oxygen partial pressure in the atmosphere, a buffer system, either CO2-CO, H2O-H2 or CO2-H2, was used. In the phase relationships in which (02) was controlled by means of mixed-gas system, P(02) measured with oxygen sensors was compared with P(02) calculated from the mixing ratios of COj/CO, H2O/H2 or CO2/H2. And when they were identical within experimental error, the phase relationships reported are given. It is almost meaningless to use the atmospheres of mixed gas systems which are not in equilibrium in the atmosphere for determining equilibrium oxygen partial pressure values of the solid phases, even if it is measured with a ( 2) sensor (Takayama and Kimizuka 1979). 

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