Ozone layer formation

As described in Chap. 1, in contrast to stratospheric chemistry that can be traced back to the 1930s when the chemical theory of ozone layer formation was published by Chapman (1930), research on chemical reaction system in the tropospheric... 

There are probably more than five million species on the Earth many of which are very similar. Moreover, as many as now exist have probably been lost. In our opinion it is not to be expected that an explanation can be given for particular species although they are connected by morphology or DNA/RNA or protein sequences. We shall turn to the problem as to why there have been and are so many species in Chapter 11. We wish to look at evolution from the point of view of very general chemical and physical principles which is the same thermodynamic approach that we used in the analysis of formation of clouds or the ozone layer in Section 3.4. We observe immediately that the major groups in Table 4.2 have all advanced and have not displaced one another. 

Both processes are switched on by the absorption of short-wavelength radiation X < 240 nm for H20 and X < 230 nm for C02. On the assumption that H atoms escape from the atmosphere, there is a net gain in oxygen to the atmosphere. Reactions of O atoms and 02 chemistry would then lead to the formation of a small ozone layer with a low ozone concentration. 

The Stratospheric Ozone Layer Its Photochemical Formation and Degradation... 

Volatile organic compounds (VOC) contribute to the formation of tropospheric ozone (summer smog). Certain halogenated hydrocarbons (e.g. CFCs) also destroy the stratospheric ozone layer. Chlorinated solvents are hazardous to water and, if disposed of incorrectly (e.g. burning), may emit highly toxic substances (e.g. dioxins). 

There is a vaiiety of problems associated with air pollution, starting from photochemical smog, ozone formation, and acid rain at a regional level, to the greenhouse effect and ozone-layer depletion at a global level. These problems have an adverse impact on both environment and public health (Table 1.1) the last two problems are a threat to life on Earth generally. 

A few comments on nitrous oxide Nitrous oxide (NzO) is a gas produced mainly through natural sources. However, generally, motor vehicles and combustion processes contribute to its formation in urban areas. Unfortunately, it is involved adversely in the two global environmental problems it contributes to the greenhouse effect and penetrates into the stratosphere, destroying the ozone layer. 

What sort of chemistry controls the formation of an ozone layer What effects might man-made chemicals have on the ozone layer These... 

The residence times of SO2 and H2S04 in the troposphere are typically only a few days, but sulfuric acid aerosols reaching the stratosphere can be very persistent together with nitric acid, they provide the solid surfaces in polar stratospheric clouds on which reaction 8.9 and related processes occur heterogeneously. Indeed, studies suggest that NOx emissions of commercial supersonic aircraft in the lower stratosphere may pose less of a threat to the ozone layer than previously supposed however, the accompanying formation of sulfuric and nitric acid aerosols may exacerbate ozone loss by increasing the available catalytic surface area. 

It is a matter of conjecture as to whether sunlight was involved in the buildup of early organic molecules which eventually formed DNA, RNA and proteins. Photosynthetic bacteria may well have been the very first independent life forms, and from the time of the growth of green plants the atmosphere must have become gradually richer in oxygen, since it appears as a byproduct in the major process of photosynthesis. It is generally accepted that early life developed in the oceans, and it may be surmised that its eventual development on land was made possible by the formation of the protective ozone layer in the upper atmosphere. 

Depletion of stratospheric ozone layer Global warming Formation of photochemical pollutants Acidification Pluman toxicity... 

There are various approaches to parameterizing the process of formation and destruction of the ozone layer. The difficulty of deriving dynamic models of the ozone cycle in the atmosphere has to do with the participation in the cycle of more than 75 chemical reactions, a qualitative and quantitative description of which is impossible without deriving detailed models of the many minor gas components of the atmosphere. Nevertheless, there are empirical models of the ozone layer, which make it possible, under the present climatic situation, to obtain adequate spatial distributions of ozone. For instance, Bekoryukov and Fedorov (1987) derived a simple empirical model of total ozone content confirmed by observational data for the Southern Hemisphere ... 

In the precambrian (or on present day Mars), the absence, of an ozone layer allowed solar UV radiation with energies as high as 40,000 cm"1 (0.25 microns). Photoreduction transitions via the Fe(3d) to Fe(4s) transition may have been very significant. The photochemical oxidation of Fe2+, and the precipitation of FeOOH, may be the origin of the extensive precambrian banded iron formations (38-40). Moreover, the photooxidation of Fe2 may have reduced C02 to organic molecules (37.41) ... 

Another important mutagen is ultraviolet light. Recent concern about the depletion of the atmospheric ozone layer by chlorofluorocarbon compounds (CFCs) is due to the role of the ozone in absorbing UV radiation before it can cause mutations in the organisms at the earth s surface. All the DNA bases efficiently absorb UV and become chemically reactive as a result. The formation of pyrimidine dimers from adjacent thymidine residues in DNA interferes with replication and transcription of DNA. See Figure 8-14. 

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