Oxygen atmospheric fluctuation

In addition to pollution episodes, risks may arise due to atmospheric oxygen concentrations fluctuating beyond its normal level of 21% posing health (page 72) or fire hazards. Eire and explosion dangers may also arise from the presence of flammable gases, vapours, or dusts in the atmosphere (Chapter 6). 

Fig. 8.7 The recent changes of atmospheric oxygen. This graph shows how the amount of oxygen in the atmosphere (expressed as a percentage of its present-day value) has evolved with time. Note that the atmosphere contained essentially no oxygen until about 2 billion years ago and then rose rapidly for the next 1.5 billion years but with fluctuations have moved towards the 21% of today. (Adapted from Bemer, see Further Reading.)...

Figure 3 shows a TWC system and a typical performance of the TWC. The three components are highly purified over the catalyst around the stoichiometric point. The oxidizing and reducing components have almost the same chemical equivalent in the narrow shadowed region, and CO, HC and NOx are converted into H20, C02 and N2 (Fig. 3b). The atmosphere of the TWC is automatically controlled around the stoichiometric point by the TWC system. The flow rate of air is monitored and the fuel injection is controlled by a computerized system to obtain a suitable A/F ratio (Fig. 3c). The signal from oxygen sensor is used as a feedback for the fuel and air injection control loop. Therefore, the exhaust gases are fluctuating streams between oxidizing and reducing periodically and alternatively.

Analyses of the soil atmosphere show that it suffers greater fluctuations in composition than ordinary air. As a rule it contains less oxygen, but nearly ten tunes as much carbon dioxide as the air, as shown by the following data 1... 

The most startling result of the ice-core analyses is that atmospheric CO2 concentrations 30 to 40 thousand years ago apparently varied by nearly a factor of 2 over periods of less than a few hundred years (Figures 3 and 4) (Oeschger and Stauffer, 1985). That these apparent fluctuations are real is indicated by measurements of oxygen isotopes which reflect the... 

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