title: High Mercury Wet Deposition at a "Clean Air" Site in Puerto Rico.
abstract: Atmospheric mercury deposition measurements are rare in tropical latitudes. Here we report on seven years (April 2005 to April 2012, with gaps) of wet Hg deposition measurements at a tropical wet forest in the Luquillo Mountains, northeastern Puerto Rico, U.S. Despite receiving unpolluted air off the Atlantic Ocean from northeasterly trade winds, during two complete years the site averaged 27.9 μg m(-2) yr(-1) wet Hg deposition, or about 30% more than Florida and the Gulf Coast, the highest deposition areas within the U.S. These high Hg deposition rates are driven in part by high rainfall, which averaged 2855 mm yr(-1). The volume-weighted mean Hg concentration was 9.8 ng L(-1), and was highest during summer and lowest during the winter dry season. Rainout of Hg (decreasing concentration with increasing rainfall depth) was minimal. The high Hg deposition was not supported by gaseous oxidized mercury (GOM) at ground level, which remained near global background concentrations (<10 pg m(-3)). Rather, a strong positive correlation between Hg concentrations and the maximum height of rain detected within clouds (echo tops) suggests that droplets in high convective cloud tops scavenge GOM from above the mixing layer. The high wet Hg deposition at this "clean air" site suggests that other tropical areas may be hotspots for Hg deposition as well.
authors.affiliation: U.S. Geological Survey, P.O. Box 628, Montpelier, Vermont 05601, United States.
authors.forename: James B
authors.initials: JB
authors.lastname: Shanley
authors.affiliation: U.S. Geological Survey, El Paso, Texas 79968, United States.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Engle
authors.affiliation: U.S. Geological Survey, Reston, Virginia 20192, United States.
authors.forename: Martha
authors.initials: M
authors.lastname: Scholl
authors.affiliation: U.S. Geological Survey, Middleton, Wisconsin 53562, United States.
authors.forename: David P
authors.initials: DP
authors.lastname: Krabbenhoft
authors.affiliation: Eurofins Frontier Global Sciences Inc., Bothell, Washington 98011, United States.
authors.forename: Robert
authors.initials: R
authors.lastname: Brunette
authors.affiliation: University of Illinois , Champaign, Illinois 61820, United States.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Olson
authors.affiliation: University of Vermont , Burlington, Vermont 05405, United States.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Conroy
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001267:Atlantic Ocean; D004784:Environmental Monitoring / Q000379:methods; D005431:Florida; D065928:Forests; D005740:Gases / Q000032:analysis; D008628:Mercury / Q000032:analysis*; D017669:Mercury Compounds / Q000032:analysis; D010087:Oxides / Q000032:analysis; D011647:Puerto Rico; D011891:Rain; D012621:Seasons; D014329:Tropical Climate; D014919:Wind
chemical_list: D000393:Air Pollutants; D005740:Gases; D017669:Mercury Compounds; D010087:Oxides; D008628:Mercury; C019468:mercuric oxide