Biogenic trace gases

Livingston G, Hutchinson G. Enclosure-based measurement of trace gas exchange applications and sources of error. In Matson PA, Harris RC, editors. Biogenic Trace Gases Measuring Emissions from Soil and Water. Osney Mead, Oxford Blackwell Sciences Ltd. 1995. pp. 14r-51. 

CO2, and has an average residence time in the atmosphere of 5-10 years. Carbon monoxide has an atmospheric residence time of only a few months. Its low concentration, —0.1 ppm, and its short residence time result from its chemical reactivity with OH radicals. Carbon monoxide is not a greenhouse gas, but its chemical reactivity affects the abundances of ozone and methane which are greenhouse gases. Non-methane hydrocarbons, another unstable form of carbon in the atmosphere, are present in even smaller concentrations. The oxidation of these biogenic trace gases is believed to be a major source of atmospheric CO, and, hence, these non-methane hydrocarbons also affect indirectly the Earth s radiative balance. 

Chanton j. P. and Whiting G. J. (1995) Trace gas exchange in freshwater and coastal marine environments ebullition and transport by plants. In Biogenic Trace Gases Measuring Emissions from Soil and Water (eds. P. A. Matson and R. C. Harriss), pp. 98-125. Blackwell Science, Oxford. 

Matson, P. A. and R. C. Harriss, Eds. (1995) Biogenic trace gases Measuring emissions from soil and water (Ecological methods and concepts). Wiley-Blackwell, 408 pp. 

Matson, P., Biogenic Trace Gases Measuring Emissions from Soil and Water, Blackwell, Carlton South, Australia, 1995. 

Isoprene is a eonjugated diene (2-methyl-buta-1,3-diene), volatile and hardly soluble in water under normal pressure it boils at 34 C (Merck, 1999) and dissolves up to 1.47x10 M at 21.5 C, with a Henry s constant of 0.027 mole kg atm at 25 C (NIST, 2001). Isoprene is a metabolite in plants, microbes, animals and humans, and a major biogenic trace compound emitted to the atmosphere. It is very reactive towards atmospheric gas-phase oxidants such as hydroxyl and nitrate radicals or ozone. At higher concentrations, 220 - 7000 ppm, it is carcinogenic to rodents and possibly carcinogenic to humans (Melnick and Sills, 2001). 

In addition to the important role biogenic terpenes play in gas-hase chemistry, their impact also extends to heterogeneous air chemistry. Although Went (1960) linked the formation of the blue haze over coniferous forests to the biogenic emission of 20 monoterpenes over 40 years ago, it was not until recently that terpenes received their due attention with respect to their role in secondary organic aerosol (SOA) formation. O Dowd et al. (2002) reported that nucleation events over a boreal forest were driven by the condensation of terpene oxidation products. Formaldehyde (HCHO) is a high-yield product of isoprene oxidation. The short photochemical lifetime of HCHO allows the observation of this trace gas to help constrain isoprene emissions (Shim et al. 2005). 

N2O is an otherwise relatively unreactive trace gas, whose main source is biogenic emission. Each of the reagent species (OH, HO2, H, NO2) themselves undergo many other reactions besides those shown, so that there is an intricate web involved in the final balance of O3 in the stratosphere as a function of height, season, time of day and location. Model predictions of ozone depletion, not surprisingly, are very sensitive to the accuracy of laboratory kinetic data and the assumptions and approximations applied to these systems. 

The hydrate recovered consisted of methane ( 99%), with minor to trace amounts of carbon dioxide (1.22%), ethane (86 ppmv), propane (2 ppmv), with a volumetric ratio of methane to water of 154. The chlorinity concentration (57.2 mM) of water collected indicated that the sample was a mixture of 10% pore water and 90% freshwater. The gas water ratio exceeded 170, higher than any previously reported for in situ hydrates. The C1/C2 ratio was 11,500, compared to a headspace value three times lower however, both gas ratios indicate biogenic gas. 

Van Kranendonk, M.J., Webb, G.E., and Kamber, B.S., 2003. Geological and trace element evidence for a marine sedimentary environment of deposition and biogenicity of 3.45 Ga stromatolitic carbonates in the Pilbara Craton and support for a reducing Archaean ocean. Geobiology, 1, 91-108. 

This book covers homogeneous gas-phase kinetics important in the atmosphere, which has been almost established, and provides the solid scientific bases of oxidation of trace gases and oxidant formation. Nevertheless, unresolved problems remain, for example, unsatisfactory reproduction of observed OH/HO2 mixing ratio by model simulation under certain conditions, and oxidation mechanisms involving isoprene, terpenes and other biogenic hydrocarbons, and anthropogenic aromatic hydrocarbons. Therefore, descriptions of these topics are not completed in the book. Heterogeneous reaction chemistry is not covered well except for the chemistry on polar stratospheric clouds (PSCs) and reactive uptake coefficients of selected... 

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