Emissions of natural volatile organohalogens in Arctic and Sub-Arctic vegetation types
Ole Stig Jacobsen, Senior Scientist, GEUS/CENPERM
Today it is generally recognized that the volatile organic halogen compounds as chloroform has a powerful effect on atmospheric chemistry, including the degradation of the protective ozone layer in the upper atmosphere. Many of these compounds are now known to be produced by natural processes in the soil and the sea. However, there is still uncertainty about emission and distribution of the naturally production of some of these compounds, in particular with regard to the fate and emissions from arctic and subarctic rural areas. The present project attempted to clarify some of these processes by examining the natural production and fate of the volatile organic halogen compounds in the arctic and subarctic vegetation areas. In addition, we examined some of the biological processes and environmental factors involved in the formation of organic halogen compounds. The project was an integration of field measurements (Kangerlussuaq, Disko and Narsarsuaq, Greenland and Abisko, northern Sweden) and laboratory tests, combined with simplified model calculations which include the measurement of climatic factors such as temperature and precipitation. We have at all 10 sites seen a positive emission of chloroform. Of all possible halogenated substances we were able to detect, only chloroform and in a few cases chlorobromoform were emitted to the atmosphere. The emission from the 45 individual fixed plots showed a very large variation, but in general plots with low emissions continued to have low emissions during the project period. The general trend is for nearly all arctic and subarctic sites a significantly lower emission than our previous measurements in the Danish ecosystems and what is measured in temperate forests. The measurements have been made on Disko and Zackenberg shows the same trend. However, at two sites, birch forest and pine forest at Abisko, the emissions were of the same order as found in Danish forest. We did not by this study to identify which parameters biotic / abiotic as within the same vegetation type gave the large variation in emission. However we did determine the temperature dependency of emission.
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