Oxygen altitude

Oxygen occurs free in the atmosphere (21% by volume. 23 by weight). The proportion is constant over the earth s surtace it is also constant for many miles upwards, because the turbulence of the atmosphere prevents the tendency for the lighter gases, for example helium, to increase in amount at higher altitudes. 

Table 2. Altitude Correction Factors for Oxygen Transfer...

Life-Support Applications. Exploration of outer space by humans has focused considerable attention on maximum as weU as minimum limits in the oxygen content of life-support atmospheres. Above the earth, both the atmospheric pressure and the partial pressure of oxygen decrease rapidly. The oxygen content of air remains constant at 20.946% to an altitude of ca 20 km, after which it decreases rapidly (1). 

Human evolution has taken place close to sea level, and humans are physiologically adjusted to the absolute partial pressure of the oxygen at that point, namely 21.2 kPa (159.2 mm Hg), ie, 20.946% of 101.325 kPa (760 mm Hg). However, humans may become acclimatized to life and work at altitudes as high as 2500—4000 m. At the 3000-m level, the atmospheric pressure drops to 70 kPa (523 mm Hg) and the oxygen partial pressure to 14.61 kPa (110 mm Hg), only slightly above the 13.73 kPa (102.9 mm Hg) for the normal oxygen pressure in alveolar air. To compensate, the individual is forced to breathe much more rapidly to increase the ratio of new air to old in the lung mixture. 

This cycle is terrninated by the reaction of chlorine atoms with methane Cl + CH — HCl + CH3. The importance of this cycle depends on the avadabiLity of oxygen atoms and varies with altitude as well as the time of year it accounts for only 5% of the halogen-controUed loss at 15 km, but increases to 25% at 21 km. 

The following mechanisms are more important for explaining ozone destmction at lower altitudes, where the avadabiLity of oxygen atoms is limited ... 

The oxygen sensor closed loop system automatically compensates for changes in fuel content or air density. For instance, the stoichiometric air/fuel mixture is maintained even when the vehicle climbs from sea level to high altitudes where the air density is lower. 

Levels below 19.5% oxygen ean have detrimental effeets if the body is already under stress, e.g. at high altitudes. Exposures below 18% should not be permitted under any eireumstanee. Other ehemieals, e.g. earbon monoxide, result in toxie anoxia due to damage of the body s oxygen transport or utilization meehanism. 

Ozone is a highly reactive molecule composed of three atoms of oxygen. Ozone concentrations vary by geographical location and by altitude. In addition, ozone exerts a different climate-forcing effect, depending upon altitude. 

The most important gas on the planet is the atmosphere, a thin layer of gas held by gravity to the surface of the Earth. Half the mass of the atmosphere lies below an altitude of 5.5 km. If we were to look from a point where the Earth appears to be the size of a basketball, the atmosphere would appear to be only 1 mm thick (Fig. 4.1). Yet this delicate layer is vital to life it shields us from harmful radiation and supplies substances needed for life, such as oxygen, nitrogen, carbon dioxide, and water. 

Leger, L. Oxygen Atom Reaction with Space Shuttle Materials at Orbital Altitudes, NASA Technical Memorandum 58246, May 1982... 

The thermosphere is the outermost part of the atmosphere, above an altitude of about 85 km. Here, molecules of nitrogen and oxygen absorb X-ray radiation coming from the sun. These photons have enough energy to ionize molecules and to break chemical bonds. Here are two examples ... 

Why is the ozone layer confined to one region of the atmosphere The production of ozone requires both a source of oxygen atoms and frequent collisions between the atoms and the molecules that make up the atmosphere. At altitudes lower than 20 km, all the light energetic enough to split oxygen molecules into oxygen atoms has already... 

The influence of other active components, such as 1, OH, H on a semiconductor sensor, with other conditions being the same, is comparable with the influence of atomic oxygen [50]. Contribution of N and OH is proportional to their relative contents (compared to that of atomic oxygen) in the atmosphere and may become essential at altitudes lower than 60 - 70 km. The use of selective detectors excludes the influence of atomic hydrogen. Studies of adsorption of water vapours on ZnO films [50] show that their influence is negligibly small at the film temperatures below 100°C. Variations of electric conductivity of the films under the influence of water vapours and of an atomic oxygen are comparable at the ratio of their concentrations [H20]/[0] = 10" . 

The low concentrations of ozone normally present in the atmosphere are sufficient to cause severe oxidation and cracking in polyolefins (2-13) and many other polymers such as polystyrene (6,11,12,14.15). poly(vinyl chloride) ( y, J 2,J 6) and rubbers (11,12,17-20). Where the ozone concentration is increased by air pollution, higher altitudes or the present of electrical machinery, the rate of degradation considerably increases.The prevention of such degradation represents a matter of considerable economic interest since it can greatly improve service life of polymers and plastics. An additional application of this research is to apprise the suitability of polymers for upper atmosphere application (Space Shutle flights) where a plentitude of ozone and atomic oxygen prevails. 

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