Quantifying remoteness from emission sources of persistent organic pollutants on a global scale

One of the four screening criteria that are assessed when a chemical substance is nominated for international regulation under the Stockholm Convention is potential for long-range transport. Measured levels of a chemical in locations distant from sources can be used as evidence of long-range environmental transport, but until now, there has been no quantitative measure of the distance of a location from likely source areas of chemicals. Here we use a global atmospheric transport model to calculate atmospheric concentrations for a set of volatile tracers that differ in their effective atmospheric residence time. We then derive an empirical relationship to express these concentrations as a function of the atmospheric residence time and a location-specific parameter, the remoteness index, RI. We present maps of RI for two generic emissions scenarios that represent areas for emissions of industrial and technical chemicals and pesticides, respectively. Our results can be used to better interpret spatial patterns of measured and modeled concentrations of chemicals in the global environment and to derive long-range transport potential metrics for specific substances. We thus provide, to our knowledge for the first time, a description of remoteness that is applicable to measurement sites of continental- and global-scale monitoring programmes. Our results can be used to plan future measurement campaigns and extend monitoring networks.