Wet Mercury Deposition to a Remote Islet (Pengjiayu) in the Subtropical Northwest Pacific Ocean in 2009-2013

Abstract:

One hundred and ninety-one weekly rainwater samples were collected between 2009 and 2013 at a weather station (25º37’46”N, 122º4’16.5”E, 101.7 m a.s.l.) in Pengjiayu, a remote islet in the subtropical Northwest (NW) Pacific Ocean with an area of 1.14 km², to study the distribution of rainwater mercury (Hg) concentrations and associated wet deposition fluxes. This is likely one of the longest dataset concerning wet Hg deposition to the subtropical NW Pacific Ocean downwind of the East Asian continent, which is the major source region for Hg emissions worldwide. Sample Hg concentrations ranged from 1.32 to 49.56 ng L^-1, with an overall volume-weighted mean (VWM) concentration of 7.78 ng L^-1. The annual VWM Hg concentrations were 8.85, 9.16, 7.08, 8.01 and 5.78 ng L^-1 for 2009, 2010, 2011, 2012 and 2013, respectively. The annual wet Hg deposition fluxes were 13.54, 20.19, 10.84, 15.57 and 11.46 μg m^-2, respectively, about 2.7-5 times the fluxes measured at sites on the Pacific coast of the USA and 1.5-2.8 times the flux measured in Bermuda, indicating higher wet Hg deposition to the NW Pacific Ocean than to the NE Pacific Ocean and the North Atlantic Ocean.