Long-distance transport (atmosphere)

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The atmospheric long-range transport (ger .: long-range atmospheric transport or long-range transport ), the airborne transport of pollutants over a long distance (typically several hundred or thousand km).

The atmosphere is one of the main transport media for pollutants. Both conversion products and the actual pollutant can be precipitated ( deposited ) in regions remote from the source . In terms of the above However, only the broad distribution of the actual pollutant can be defined under the term long-distance atmospheric transport. The prerequisite for this is that the pollutant is stable (inert) to environmental influences, i.e. H. is not subject to any chemical transformation during transport. Most of the pollutants that are stable belong to the group of persistent organic pollutants (POP) [from English. Persistent organic pollutants].

A determining factor is the proportion of a pollutant that is adsorbed on aerosols . In its adsorbed form it is - in contrast to the gas phase - from photo- oxidation , i. H. direct photolysis as well as oxidation by OH radicals or ozone .

background

The theory of long-distance transport of pollutants in the atmosphere was developed to explain the presence of pollutants far away from their areas of application.

One of the population groups most exposed to POP in the world are the Eskimos , although they themselves do not emit many of the POP.

The concentrations of pollutants such as B. DDT , lindane and other pesticides are sometimes higher in areas where they are rarely used than in tropical countries where they are used for pest control. Some areas can act as both sinks and sources of persistent organic pollutants (POP), depending on the time of year . Since this process is similar to the chemical process of distillation (first evaporating, then condensing), the process of long-distance atmospheric transport is also referred to as global distillation or the grasshopper effect.

mechanism

The theory of global distillation (also known as the grasshopper effect, grasshopper effect or cold condensation) states that pollutants can be transported to different distances in the air, depending on their physico-chemical properties (e.g. solubility , vapor pressure, etc.) before they pass through dry or moist deposition return to the earth. A pollutant can be dumped several times and remobilized (absorbed into the air) again through evaporation / evaporation . The final deposition of a pollutant that is subject to long-distance atmospheric transport takes place particularly in the polar regions, since re-evaporation / volatilization is unlikely here due to the low temperatures. Other high-altitude areas of the world, such as the Alps or the highlands of Tibet, are also affected. Substances accumulate there and are broken down even more slowly due to the low temperatures. However, new studies have shown that with most substances - exceptions are highly volatile and persistent substances such as B. chlorofluorocarbons - not the thermodynamic but the kinetic properties - the slower degradation rates at colder temperatures - are mainly responsible for the comparatively high concentrations in the polar regions.

literature

Individual evidence

  1. ↑ Carolyn J. Koester, Ronald A. Hites: Photodegradation of polychlorinated dioxins and dibenzofurans adsorbed to fly ash . In: Environmental Science & Technology . tape 26 , no. 3 , March 1, 1992, ISSN  0013-936X , p. 502-507 , doi : 10.1021 / es00027a008 .
  2. ↑ Jonathan D. Raff, Ronald A. Hites: Deposition versus Photochemical Removal of PBDEs from Lake Superior Air . In: Environmental Science & Technology . tape 41 , no. 19 , October 1, 2007, ISSN  0013-936X , p. 6725-6731 , doi : 10.1021 / es070789e .
  3. ↑ S. Schenker, M. Scheringer , K. Hungerbühler : Do Persistent Organic Pollutants reach a thermodynamic equilibrium in the global environment? Environmental Science & Technology , 2014, doi: 10.1021 / es405545w .
  4. ↑ F. Bergamin: Determined by slow degradation , ETH News, 2014.