1Independent researcher, 5785 Yonge Street, Toronto, Ontario M2M 4J2, Canada
2Air Quality Research Division, Science and Technology Branch, Environment Canada, 4905 Dufferin Street,Toronto, Ontario M3H 5T4, Canada
3Air Quality Sciences Section, Environment Canada, 45 Alderney Drive, Dartmouth, Nova Scotia B2Y 2N6, Canada
Received: 03 Jan 2013 – Discussion started: 14 Feb 2013
Abstract. Regional and local sources contributing to gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particle-bound mercury (PBM) at an urban coastal site in Dartmouth, Nova Scotia, Canada were investigated using the Concentration-Weighted Trajectory model (CWT) and Conditional Probability Function. From 2010–2011, GEM, GOM, and PBM concentrations were 1.67 ± 1.01 ng m−3, 2.07 ± 3.35 pg m−3, and 2.32 ± 3.09 pg m−3, respectively. Seasonal variability was observed, with statistically higher GEM and PBM concentrations in winter and spring and higher GOM in spring. In the CWT, concentrations are the weighting factors for the trajectory residence time in modeled grid cells, which results in the identification of source areas based on the CWT values in the grid cells. Potential source areas were identified in regions with known industrial Hg sources particularly in the fall season, but also in regions without these sources (e.g. Atlantic Ocean, northern Ontario and Quebec). CWTs for GOM and PBM that were associated with ≥ 5 kg industrial Hg emissions from 2010–2011 were statistically larger than those with zero Hg emissions, despite a lack of strong correlations. A large proportion of elevated CWTs (85–97%) was in regions with zero industrial Hg sources indicating the potential role of non-point sources, natural emissions, and residential-scale combustion. Analysis of wind data suggests that a commercial harbor and vehicular traffic were potential local sources. Evaluating modeled source areas against Hg emissions inventories was not an ideal method for assessing the CWT model accuracy because of insufficient data on Hg emissions at more precise locations.
Revised: 21 May 2013 – Accepted: 23 May 2013 – Published: 23 Jun 2013
Cheng, I., Zhang, L., Blanchard, P., Dalziel, J., and Tordon, R.: Concentration-weighted trajectory approach to identifying potential sources of speciated atmospheric mercury at an urban coastal site in Nova Scotia, Canada, Atmos. Chem. Phys., 13, 6031-6048, doi:10.5194/acp-13-6031-2013, 2013.