Global multimedia source-receptor relationships for persistent organic pollutants during use and after phase-out

Chemicals that are persistent in the atmosphere can be transported long distances and across international boundaries. Therefore, information about the fraction of local versus imported air pollution is required to formulate regulations aimed at controlling pollutant levels. The objective of this work is to illustrate the capabilities of a dynamic global–scale multimedia model to calculate source–receptor relationships for persistent organic pollutants that cycle between air, water, soil and vegetation in the global environment. As exemplary case studies, we present model calculations of time–evolving source–receptor relationships for PCB28, PCB153, α–HCH and β–HCH over the duration of their usage, phase–out and a post–ban period. Our analysis is geographically explicit, and elucidates the role of primary versus secondary sources in controlling the levels of air pollution. Our case studies consider source–receptor relationships between the four regions defined by the Convention on Long–range Transboundary Air Pollution Task Force on Hemispheric Transport of Air Pollution, as well as the Arctic as a remote receptor region. We find source–receptor relationships that are highly variable over time, and between different regions and chemicals. Air pollution by PCBs in North America and Europe is consistently dominated by local emissions, whereas in East– and South–Asia extra–regional sources are sometimes major contributors. Emissions of α–HCH peak at different times in the four regions, which leads to a phase of high self–pollution in each region, and periods when pollution enters mainly from outside. Compared to α–HCH, air pollution with the less volatile and more persistent β–HCH is more strongly determined by secondary emissions near source areas throughout its use history. PCB concentrations in Arctic air are dominated by emissions transported from North America and Europe from 1930 to 2080, whereas for HCHs each of the source regions contributes a high share at some point between 1950 and 2050.