Crutzen

R. A. Murgatroyd, G.M. Worrall, und S. Crutzen Lessons leamt from the RISC 111 study of the influence of human factors on inspection reliability. 6 European Conference on Nondestructive Te.sting, Nice. 1994, Vol. 2, p 989-993... 

O. Farli, R.M. Denys, S. Crutzen, Development of Acceptance Criteria for Pipeline Girth Weld Defects. European Conference on Non-Destructive Testing, Copenhagen, 26 - 29 May 1998... 

Crutzen P J 1995 Overview of tropospheric chemistry developments during the past quarter century and a look ahead Faraday Disouss. 100 1-21... 

Figure 2 Estimated methane produetion by domestieated animals and humans. (From data of Crutzen et al, 1986)...

F. S. Rowland and M. Molina showed that man-made chlorofluorocarbons, CFCs, could catalytically destroy ozone in the stratosphere (Nobel Prize for Chemistry, with P. Crutzen, 1995). 

M. J. Molina and F. S. Rowland, Nature 249, 810-12 (1974). (Shared 1995 Nobel Prize for Chemistry with P. Crutzen.)... 

The decrease is continuing due to global adherence to the provisions of the Montreal (1989) and London (1990) Protocols, and it is hoped that the most deleterious CFCs will eventually be phased out completely. As a result of their work, Rowland and Molina were awarded the Nobel Prize for Chemistry for 1995 (together with P. Crutzen, who showed how NO and NO2 could similarly act as catalysts for the depletion of stratospheric ozone). Several excellent accounts giving more details of the chemistry and meteorology involved are available. 

P. Crutzen (Max Planck Institute for Chemistry, Mainz), M. Molina (Massachusetts Institute of Technology) andF. S. Rowland (Irvine, California) work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone. 

The two scientists who first suggested (in 1974) that CFCs could deplete the ozone layer, F. Sherwood Rowland (1927-) and Mario Molina (1943-), won the 1995 Nobel Prize in chemistry, along with Paul Crutzen (1933—), who first suggested that oxides of nitrogen in the atmosphere could catalyze the decomposition of ozone. 

Mario Molina and Sherwood Rowland used Crutzen s work and other data in 1974 to build a model of the stratosphere that explained how chlorofluorocarbons could threaten the ozone layer. In 1985, ozone levels over Antarctica were indeed found to be decreasing and had dropped to the lowest ever observed by the year 2000, the hole had reached Chile. These losses are now known to be global in extent and it has been postulated that they may be contributing to global warming in the Southern Hemisphere. 

The concentration of ozone in the stratosphere is lower than predicted from reactions 1-4. This is due to the presence of trace amounts of some reactive species known as free radicals. These species have an odd number of electrons and they can speed up reaction 4 by means of catalytic chain reactions. Nitrogen oxides, NO and NO2, which are naturally present in the stratosphere at levels of a few parts per billion (ppb), are the most important catalysts in this respect. The reactions, first suggested by Paul Crutzen (2) and by Harold Johnston (3) in the early 1970 s, are as follows ... 

Figure 7-11 and its caption (Crutzen, 1983) depict the most important of the gas phase and photochemical reactions in the atmosphere. Perhaps the single most important interaction involves the hydroxyl free radical, OH-. This extremely reactive radical is produced principally from the reactions of electronically excited atomic oxygen, 0( D), with water vapor. Photo-... 

Fig. 7-11 Compilation of the most important photochemical processes in the atmosphere, including estimates of flux rates expressed in moles per year between the earth s surface and the atmosphere and within the atmosphere. (Modified with permission from P. J. Crutzen, Atmospheric interactions - homogeneous gas reactions of C, N, and S containing compounds. In B. Bolin and R. Cook (1983). "The Major Biogeochemical Cycles and Their Interactions," pp. 67-112, John Wiley, Chichester.)...

Fig. 11-6 Concentrations of gases in the smoke from an experimental fire of Trachypogon grass from Venezuela as a function of time and the stack gas temperature. The dotted line separates the flaming phase from the smoldering phase. Concentrations are in percent by volume for CO2, in volume mixing ratios (ppm) for the other species (1% = 10000 ppm). (Used with permission from Crutzen and Andreae (1990). Science 250 1669-1678, AAAS.)...

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

The role of carbon dioxide in the Earth s radiation budget merits this interest in atmospheric CO2. There are, however, other changes of importance. The atmospheric methane concentration is increasing, probably as a result of increasing cattle populations, rice production, and biomass burning (Crutzen, 1983). Increasing methane concentrations are important because of the role it plays in stratospheric and... 

Crutzen, P. J. and Andreae, M. O. (1990). Biomass burning in the Tropics impact on atmospheric chemistry and biogeochemical cycles. Science 250, 1669-1678. 

Seiler, W. and Crutzen, P. J. (1980). Estimates of gross and net fluxes of carbon between the biosphere and the atmosphere from biomass burning. Climat. Change 2, 226-247. 

Photochemistry plays a significant role in nitrogen s atmospheric chemistry by producing reactive species (such as OH radicals). These radicals are primarily responsible for all atmospheric oxidations. However, since the photochemistry of the atmosphere is quite complex, it will not be dealt with in detail here. For an in-depth review on tropospheric photochemistry, the reader is referred to Logan et al. (1981), Finlayson-Pitts and Pitts (1986), Crutzen and Gidel (1983) or Crutzen (1988). 

The lifetime of gaseous NO in the troposphere is on the order of 1-30 days (Sdder-lund and Svensson, 1976 Carrels, 1982 Crutzen, 1988). 

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