Transport of pollutants in the atmosphere
The atmosphere is the most common and quickest mode of transport for pollutants. It may take only a few days or weeks for the pollutants to reach the Arctic from certain areas. Volatile and semi-volatile compounds are transported in the atmosphere.
Airborne pollutants are carried to the Arctic on air currents in the atmosphere. For example, it is estimated that some 45 % of long-transported PCBs reach Svalbard by direct air transport. Some types of pollution, particularly volatile and semi-volatile organic compounds and mercury, are transported in gaseous form and behave differently from substances that are bound to particles and aerosols. As the temperature gradually drops, the pollutants become bound to particles or dust and fall to the ground as rain or snow. This process may be repeated through seasonal cycles, so that ice melting, autumn storms and other events whirl the particles up so that they may be transported further in the atmosphere. Persistent organic pollutants (POPs) and mercury can repeat this process many times and spread over the entire planet. However, the climatic conditions at high latitudes make it more difficult for them to convert into a gaseous form again when they have been precipitated so that they are easily accumulated in these regions.
The part played by the atmosphere as a means of transport varies from season to season. The transport is greatest in winter and spring, and least in summer, because the properties of the air masses differ in different seasons. The Arctic winter is characterised by a stable High over the North Pole which “captures” the air masses for a long period. The air therefore remains stable for a long time, giving plenty of time for pollutants to be deposited on ice, sea or land. In summer, temperature changes give the air masses more energy which, in turn, generates more dynamic weather instead of the static high pressure.
Climate changes that affect the weather systems may have an effect on one or more of the processes which control the transport or deposition of the pollutants. Much more needs to be learnt about this, and a great deal of research and modelling are taking place to elucidate the consequences of climate changes for the atmospheric transport of pollution. Existing knowledge suggests that POPs, for example, “captured” in water and ice will be revitalised in the atmosphere as the temperature rises, and there is evidence that such a process has already begun for some of the most volatile substances. A recently published study indicates that several POPs have been remobilised in the atmosphere during the last two decades as a result of climate change, and several other studies have shown that climate change has already had significant consequences for many aspects of the transport and remobilisation of mercury, partly in association with distribution and transport in the sea-ice-air interface. However, another recently published study indicates that the indirect consequences of climate change (changes in agriculture, utilisation of resources, etc.) will have at least as great an effect on the distribution and deposition of pollutants as the direct changes.
- Jianmin Ma, Hayley Hung, Chongguo Tian & Roalnd Kellenborn 2011. Revolatilization of persistent organic pollutants in the Arctic induced by climate change. Nature Climate Change 1, 255–260, 2011. DOI:10.1038/nclimate1167
- Gary A. Stern, Robie W. Macdonald, Peter M. Outridge, Simon Wilson, John Chételat, Amanda Cole, Holger Hintelmann, Lisa L. Loseto, Alexandra Steffen, Feiyue Wang, Christian Zdanowicz 2012. How does climate change influence arctic mercury?. Science of The Total Environment 414, 22–42, 2012. DOI:10.1016/j.scitotenv.2011.10.039
- Roland Kallenborn et al. 2012. Long-term monitoring of persistent organic pollutants (POPs) at the Norwegian Troll station in Dronning Maud Land, Antarctica. Atmos. Chem. Phys. (13): 6983–6992. DOI:10.5194/acp-13-6983-2013