In search of potential source regions of semi-volatile organic contaminants in air in the Yukon Territory, Canada from 2007 to 2009 using hybrid receptor models

Environmental context Some long-lived organic contaminants, such as chlorinated organics, brominated flame retardants and polycyclic aromatic hydrocarbons, can undergo transport through the atmosphere to remote regions. A series of measurements of these compounds taken over almost 3 years in the air at a remote location was combined with meteorological data to try to reveal potential source areas. After adjusting several parameters to optimise the method’s ability to identify sources it was found that for most contaminants no definitive sources are revealed. Abstract A suite of brominated flame retardants, chlorinated organic pesticides and some metabolites thereof were analysed in week-long and day-long air samples collected at Little Fox Lake in Canada’s Yukon Territory from 2007 to 2009. Several trajectory-based methods for source region identification were applied to this dataset, as well as to polycyclic aromatic hydrocarbon (PAH) concentrations in those same samples reported previously. A type of concentration weighted trajectory (CWT) analysis, using a modified grid to avoid difficulties near the Earth’s poles, and removing trajectory endpoints at altitudes greater than 700m did not identify distinct source regions for most analytes. Decreasing the spatial resolution of the grid made interpretation simpler but reinforced patterns that may have stemmed from single trajectories. The potential source contribution function (PSCF) is similar to CWT but treats the concentration data categorically, rather than numerically. PSCF provides more distinct results, highlighting the Arctic Ocean as a potential source of para,para′-dichlorodiphenyldichloroethene and both northern Siberia and Canada’s Yukon and Northwest Territories as potential sources of PAHs. To simulate the uncertainty associated with individual trajectories, a set of trajectories was also generated for six points surrounding the sampling station and included in the trajectory analyses. This had the effect of smoothing the CWT and PSCF values for those analytes with no clearly definable sources, and highlighting the source regions for the two that did. For the bulk of the analytes discussed here, Little Fox Lake is well positioned to act as a background monitoring site.