Apparent change with partial pressure

Even if equilibrium had been achieved before the water mass sank, the observed water mass concentrations could exhibit apparent deviations from equilibrium, if the atmospheric pressures have changed or if the water mass temperature has been altered. Thus, deepwater that was last at the sea surface hundreds of years ago could potentially have equilibrated with the atmosphere at much different partial pressures of gases such as methane and carbon dioxide whose atmospheric levels have risen over time. For example, the partial pressure of CO2 in dry air has risen from about 280 ppm in the 1860s to 385 ppm in 2008. 

AOU is usually expressed in imits of p,mol 02/kg SW. This called an apparent utilization because it is a measure of the net difference between the AOU and NAEC. The latter is inferred from the in situ temperatme and salinity. Thus, the AOU calculation assumes that (1) the water mass had attained gaseous equilibrium with the atmosphere, (2) the partial pressure of O2 in the atmosphere has not changed since the water mass was last at the sea surfece, and (3) neither have the in situ temperature and salinity. As described in Chapter 6, this last assiunption can be violated by post-equilibration heating, such as via conduction from a hydrothermal system. This leads to an underestimate of the true NAEC, and, hence, an underestimate of the AOU. 

MCH and in H2 at temperatures below 370°C. Toluene desorption was identified as the rate-limiting step. It was found that at low pressures the reaction rate increases with MCH partial pressure, and at higher pressures there is no effect of MCH partial pressure on the reaction rate. This change in apparent order occurs at 1 mmHg MCH partial pressure approximately. On the other hand, it was also reported (15) that the hydrogen partial pressure has no effect on the reaction rate. These reaction orders close to zero for both reactant under practical conditions indicate that the platinum surface active sites are completely covered by adsorbed hydrocarbons (reactant molecules or intermediate compounds). The reaction proceeds, according to the following steps ... 

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