Study On Atmospheric Hg’s Transport In The Boundary Layer Over The Antarctic Inland And Seas And Its Air-sea Flux

Mercury(Hg)is noxious and becomes potentially bioavailable by transformation to more water-soluble and toxic compounds.Due to its ubiquitous presence and neurotoxicity,mercury attracts considerable interest with respect to a global health concern.Ehanced Hg accumulation in polar regions indicates that Hg could impact the areas far away from the major anthropogenic mercury emissions.Hg’s transport and transformation in polar regions must have its specificality as most regions are covered by snow and ice,and related to climate change.The exchange of Hg between the sea and the air plays a crucial role in Hg’s global cycle.Most of the Hg(especially the reactive form)deposited in the ocean is lost via gas evasion by the reduction to dissoved gaseous Hg(DGM,mainly Hg0)and likely cycles between the surface ocean and the mairine boundary layer(MBL).The elemental mercury(Hg0)that is subject to re-emission from the surface ocean is not noly a main supply to Hg in the atmosphere,but also help it long-range disperse.The report was supported by the yearly Chinese National Antarctic Research Expedition(CHINARE).Study area includes:Antarctic inland;the Southern Ocean;the Central Indo-Pacific.Here we focus on the transport of atmospheric Hg in the marine boundary layer and the boundary layer in polar regions.also the air-sea flux of mercury exchange.Main conclusions as below:(1)Total gaseous mercury(TGM)in the atmospheric boundary layer was investigated along a transect from coastal to central Antarctic from December 16,2012 to February 6,2013.TGM varied considerably from 0.32 to 2.34 ng m-3 with a mean value of 0.91 ng m-3.Spatially,relatively high values occurred near the coastal region and on the central plateau with altitude higher than 3000m above sea level.This distribution pattern cannot be accounted for simply by the influence of mercury emission from the ocean.Changes in TGM were also found to be related to the topography.TGM was higher in the inland flat region(290-800 km from the coast)than in the inland transition zones with steep slopes(800-1000 km from the coast).Temporally,diurnal cycling of TGM was clearly observed at Kunlun Station,with the lowest value occurring typically at midnight,and the peak value at midday.This diurnal pattern was attributed to the reemission of gaseous elemental mercury(GEM)from the snow pack,the oxidization of GEM and convective mixing.(2)Gaseous elemental mercury(GEM)in the marine boundary layer(MBL),and dissolved gaseous mercury(DGM)in surface seawater of the Southern Ocean were measured in the austral summer from December 13,2014 to February 1,2015.GEM concentrations in the MBL ranged from 0.39 to 1.92 ng m-3(mean ± standard deviation:0.93 ± 0.19 ng m-3),whereas DGM concentrations in surface seawater ranged from 7.0 to 75.9 pg L-1(mean ± standard deviation:23.7 ± 13.2 pg L-1).The occasionally observed low GEM in the MBL suggested either the occurrence of atmospheric mercury depletion in summer,or the transport of GEM-depleted air from the Antarctic Plateau.Elevated GEM concentrations in the MBL and DGM concentrations in surface seawater were consistently observed in the ice-covered region in Ross Sea implying the influence of the sea ice environment.Diminishing sea ice could cause more mercury evasion from the ocean to the air.Using the thin film gas exchange model,the air-sea fluxes of gaseous mercury in non-ice-covered area during the study period were estimated,revealing GEM(re-)emission from the East Southern Ocean in summer.(3)We found clearly shifting GEM concentrations over the equatorial region in Central Indo-Pacific,approximately defined by the latitudes 3° N and 7° S,this differ with many reports that GEM decreases interhemispherically going north to south,consistent enhanced DGM in surface sea.Excluding the contribution of anthropogenic,volcanic and biomass burning emissions,the enhanced GEM in MBL in our study was likely due to the vast evasion form the surface sea.This regional effect is evident locally,and may be related to the vast deposition of Hg by the intense convective rainfall,and subsequent rapid photoreduction.It indicates that the equatorial seas are like transfer stations for atmospheric mercury’s global transport,just like a springboard for Hg’s "grasshopper-jump".(4)We develop a continuous system to sample and determine dissolved gaseous mercury(DGM),connected to a ship’s bow water system.These data,along with the GEM concentrations and ancillary meteorological data allowed us to estimate for the air-sea fluxes of mercury exchange,eg.,in the Southern Ocean and west Pacific.The aie-sea flux of Hg is mainly affected by the DGM concentrations and wind speed.High temporay and spatial variability of the DGM concentrations and the air-sea fluxes were presented in other reports and our work,more study is needed to target efforts.