Trace gases

This chapter considers the extent, mechanisms and possibilities for control of emissions of trace gases from submerged soils. The focus is on ricefields because this is where research has been most intense and because ricefields are the focus of the greatest scrutiny for possibilities to reduce emissions. 

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Laser sources that emit in the mid-ir region of the spectmm (2—5 -lm) are useful for detection of trace gases because many molecules have strong absorption bands in that region. Other appHcations include remote sensing and laser radar. Semiconductor lead—salt (IV—VI) lasers that operate CW at a temperature of 200 K and emission wavelength of 4 p.m are commercially available however, they have relatively low output powers (<1 mW) (120). 

Forests can act as sources of some of the trace gases in the atmosphere, such as hydrocarbons, hydrogen sulfide, NO, and NH3. Forests have been identified as emitters of terpene hydrocarbons. In 1960, Went (10) estimated that hydrocarbon releases to the atmosphere were on the order of 108 tons per year. Later work by Rasmussen (11) suggested that the release of terpenes from forest systems is 2 x 10 tons of reactive materials per year on a global basis. This is several times the anthropogenic input. Yet, it is important to remember that forest emissions are much more widely dispersed and less concentrated than anthropogenic emissions. Table 8-2 shows terpene emissions from different types of forest systems in the United States. 

The interactions of air pollutants with forests at low-dose concentrations result in imperceptible effects on the natural biological cycles of these species. In some instances, these interactions may be beneficial to the forest ecosystem. Forests, as well as other natural systems, act as sinks for the removal of trace gases from the atmosphere. 

What types of trace gases are released to the atmosphere by forest ecosystems ... 

Browell, E. V.. Lidar remote sensing of tropospheric pollutants and trace gases, in Proceed-... 

The above values are based on the assumption that argon is combined with nitrogen, adjusting the molecular weight to 28.16. Other gases present in the atmosphere air are normally ignored, as these represent less than 0.003% (by volume, 27.99 ppm). Table 4.5 provides some basic information on these trace gases. 

Neglects trace gases such as argon, xenon, helium, krypton and assumes dry basis. 

Naturally-occurring Trace Gases. The naturally emitted gaseous species subject to atmospheric oxidation include ... 

The Antarctic ozone hole is the result of anthropogenic release of trace gases into the atmosphere (CFCs in particular), causing a decrease in stratospheric ozone and a subsequent increase in solar ultraviolet radiation reaching the earth s surface. 

Hitchcock, D. R. Wechsler, A E. Biological Cycling of Atmospherk Trace Gases Final Report NASA Contract NASA-CR-126663 1972 pp 117-154. 

Fig. 7-8 Inverse relationship between relative standard deviation of concentration, a /c, and residence time, T, for important trace chemicals in the troposphere. (Modified with permission from C. E. Junge (1974). Residence variability of tropospheric trace gases, Tellus 26, 477-488, Swedish Geophysical Society, Stockholm.)...

Fig. 7-14 Change in the vertical distribution of temperature due to an increase in CO2 alone, and CO2 along with other radiatively important trace gases. (Reproduced with permission from Ramanathan et al. (1985), with the permission of the American Geophysical Union.)...

Junge, C. E. (1974). Residence variability of tropospheric trace gases. Tellus 26,477-488. 

Ereyer, H.-D. (1979). Atmospheric cycles of trace gases containing carbon. In The Global Carbon Cycle" (B. Bolin, E. T. Degens, S. Kempe and P. Ketner, eds), pp. 101-128. Wiley, New York. 

Meliilo, J. M., Steudler, P. A., Aber, J. D. and Bowden, R. D. (1989). Atmospheric deposition and nutrient cycling. In "Dahlem Workshop on Exchange of Trace Gases Between Terrestrial Ecosystems and the Atmosphere" (M. O. Andreae and D. S. Schi-mel, eds). Wiley Interscience Publishers, New York. 

Dickinson, R. E. and Cicerone. R. J. (1986). Future global warming from atmospheric trace gases. Nature 319,109-115. 

Other trace gases important in atmospheric chemistry and climate (for example carbonyl sulfide and carbon monoxide) may also be measured in polar ice, and development of these and other measurements is underway in a number of laboratories around the world. 

In addition to the trace gases, many impurities, both soluble chemicals and insoluble particles, transfer from the atmosphere to the ice sheets and have measurable concentrations in ice cores. Such measurements are a window onto the... 

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