Photochemical oxygen depletion

Oxygen Limitation through Photochemical Oxygen Depletion... 

During illumination of ZnO a photodesorption of oxygen occurs 34-40> (Eq.6). Both photodesorption and readsorption in the dark (Eq. 2) are fast processes they are responsible for the fast rise and fall of the surface potential. The slow rise and fall over several hours are due to a chemical reaction. In the light, a photochemical reduction of the surface takes place (Eq. 7), leading to a destruction of the chemical depletion layer, since interstitial zinc is produced. The po-... 

Explain the following concepts and keywords photooxygenation stratospheric ozone depletion singlet oxygen photochemical smog photosensitivity phototoxicity photoallergy photodynamic therapy photoinhibition chemiluminescence perepoxide. 

Oxygen consists of three stable isotopes 0, " O and " O. For most applications only the ratio between the more abundant Lso-topes, 0 and O, is measured. If all fractionation processes in the environmental system were purely mass-dependent, measurements of 0/ 0, would be redundant, as they could be predicted from the 0/ 0 ratio. However, it has recently been ob.served that photochemical exchange between O2, Oi, and CO, in the stratosphere involves mass-independent fractionation among the oxygen isotopes (1990 Thiemens et al., 1993a, b Thiemens, 1999). Thereby O2 becomes anomalously depleted, while CO2 becomes anomalously enriched. Because of this, measurements of 0/ 0 in atmospheric O2 and/or CO2 provide an independent piece of information. Conveniently, one may define an O anomaly tracer (A 0) (Thiemens et n/., 1995b)... 

Nitrous oxide contributes to ozone depletion through photochemical reactions in the stratosphere. It reacts with an oxygen atom to form NO N2O is the chief source of NO in the stratosphere through the reaction... 

Nitrogen oxides (NO, i.e., NO, NOj, N2O) are considered as major air pollutants responsible for photochemical smog, acid rain, ozone depletion, as well as climate change. The conventional route to eliminate NO pollution is to reduce NO catalytically into N2 using NH3, urea, H, CO, and hydrocarbons as reducing agents. The decomposition of N2O is a kinetically limited reaction and inhibited by the oxygen molecule produced ... 

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