Atmospheric Environment 41 (2007) 8205–8218 Estimation of mercury loadings to Lake Ontario: Results from the Lake Ontario atmospheric deposition study (LOADS) Soon-Onn Lai a , Thomas M. Holsen a,Ã , Young-Ji Han b , Philip P. Hopke c , Seung-Muk Yi d , Pierrette Blanchard e , James J. Pagano f , Michael Milligan g a Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY 13699-5710, USA b Department of Environmental Science, Kangwon National University, Chunchon 200-701, Republic of Korea c Department of Chemical Engineering and Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13699-5708, USA d School of Public Health and the Institute of Health and Environment, Seoul National University, Seoul 110-799, Republic of Korea e Environment Canada, Science and Technology Branch, 4905 Dufferin St., Downsview, Ont., Canada M3H 5T4 f Environmental Research Center, 319 Piez Hall, SUNY at Oswego, Oswego, NY 13126, USA g Department of Chemistry, SUNY at Fredonia, Fredonia, NY 14063, USA Received 13 November 2006; received in revised form 18 April 2007; accepted 23 June 2007 Abstract Atmospheric mercury (Hg) loadings to Lake Ontario were estimated using data measured at two land-based sites: Sterling, NY and Point Petre, Ont., as part of the Lake Ontario air deposition study (LOADS) between April 2002 and March 2003. These loadings were compared with those estimated using intensive data measured onboard the R/V Lake Guardian in April 2002, September 2002, and July 2003 (each approximately one week). Measured concentrations and modeled mass transfer coefficients of elemental mercury (Hg 0 ), reactive gaseous mercury (RGM) and particulate mercury (Hg (p) ) in air and total Hg in precipitation were incorporated into a total deposition model including wet deposition, air–water gas exchange and particle dry deposition. Urban/rural Hg concentration ratios were assumed based on literature values. Assuming that 10% of the lake was influenced by urban areas, the annual net Hg atmospheric loadings of wet deposition, net air–water gas exchange of Hg 0 (deposition ¼ 300 kg yr 1 and emission ¼ 410 kg yr 1 ) and RGM, and Hg (p) dry deposition to Lake Ontario were estimated to be 170, 110, 68, and 20 kg, respectively, resulting in a net loading of 150 kg yr 1 . Net Hg loadings were largest in the fall (46 kg) and smallest in the summer (20 kg). Hg 0 , wet, RGM and Hg (p) deposition contributed 55%, 30%, 12%, and 3.6% of the total Hg deposition, respectively. The net loading was found to be most sensitive to the assumed urban/rural concentration ratios, wind speed, DGM concentration and Hg 0 transfer velocity. An increase in the influence of urban areas from 0% to 30% resulted in a 90% increase in the total loading demonstrating the complexity and non-linearity of the atmospheric deposition of mercury to Lake Ontario and the importance of quantifying the urban footprint. r 2007 Elsevier Ltd. All rights reserved. Keywords: Mercury; Atmospheric deposition; Wet deposition; Dry deposition; Air–water exchange; Great Lakes ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2007.06.035 Ã Corresponding author. Tel.: +315 268 3851; fax: +315 268 7985. E-mail address: holsen@clarkson.edu (T.M. Holsen).