Atmospheric mercury accumulation and washoff processes on impervious urban surfaces Chris S. Eckley a, b, * , Brian Branfireun a , Miriam Diamond c , Peter C. Van Metre d , Frank Heitmuller d a Department of Geography, University of Toronto at Mississauga, 3359 Mississauga Road N., Mississauga, ON L5L 1C6, Canada b Natural Resources and Environmental Science, University of Nevada, Reno, 1664 N. Virginia Street, Reno, NV 89557, USA c Department of Geography, University of Toronto,100 St. George Street, Toronto, ON M5S 3G3, Canada d U.S. Geological Survey, 8027 Exchange Drive, Austin, TX 78754-4733, USA article info Article history: Received 9 February 2008 Received in revised form 7 June 2008 Accepted 9 June 2008 Keywords: Mercury Urban Deposition Washoff abstract The deposition and transport of mercury (Hg) has been studied extensively in rural environments but is less understood in urbanized catchments, where elevated atmo- spheric Hg concentrations and impervious surfaces may efficiently deliver Hg to water- ways in stormwater runoff. We determined the rate at which atmospheric Hg accumulates on windows, identified the importance of washoff in removing accumulated Hg, and measured atmospheric Hg concentrations to help understand the relationship between deposition and surface accumulation. The main study location was Toronto, Ontario. Similar samples were also collected from Austin, Texas for comparison of Hg accumulation between cities. Windows provided a good sampling surface because they are ubiquitous in urban environments and are easy to clean/blank allowing the assessment of contemporary Hg accumulation. Hg Accumulation rates were spatially variable ranging from 0.82 to 2.7 ng m 2 d 1 in Toronto and showed similar variability in Austin. The highest accumu- lation rate in Toronto was at the city center and was 5 higher than the rural comparison site (0.58 ng m 2 d 1 ). The atmospheric total gaseous mercury (TGM) concentrations were less than 2 higher between the rural and urban locations (1.7  0.3 and 2.7  1.1 ng m 3 , respectively). The atmospheric particulate bound fraction (HgP), however, was more than 3 higher between the rural and urban sites, which may have contributed to the higher urban Hg accumulation rates. Windows exposed to precipitation had 73  9% lower accumulation rates than windows sheltered from precipitation. Runoff collected from simulated rain events confirmed that most Hg accumulated on windows was easily removed and that most of the Hg in washoff was HgP. Our results indicate that the Hg flux from urban catchments will respond rapidly to changes in atmospheric concentrations due to the mobilization of the majority of the surface accumulated Hg during precipitation events. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Contemporary atmospheric mercury (Hg) concentra- tions are estimated to be three-fold higher than pre- industrial levels as a result of anthropogenic emissions (Mason et al., 1994). The majority of human exposure to Hg pollution is through the consumption of contaminated fish (Myers et al., 2000). Therefore, understanding the link * Corresponding author. Natural Resources and Environmental Science, University of Nevada, Reno,1664 N. Virginia Street, Reno, NV 89557, USA. Tel.: þ1 775 784 4966; fax: þ1 775 784 4789. E-mail address: ceckley@cabnr.unr.edu (C.S. Eckley). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.06.013 Atmospheric Environment 42 (2008) 7429–7438