Sources of atmospheric mercury in the tropics: continuous observations at a coastal site in Suriname

Abstract

Abstract. Mercury measurements at a coastal site in Nieuw Nickerie (5 • 56 N, 56 • 59 W), Suriname, provide the only continuous records of atmospheric mercury in the tropics. Here we evaluate observations of total gaseous mercury (TGM) during 2007. Nieuw Nickerie typically samples marine air from the Atlantic Ocean, with occasional influence from continental South America. Over the year, average concentrations are 1.40 ng m −3 . As the intertropical convergence zone passes over Suriname twice each year, the site samples both northern and southern hemispheric air masses. We use back trajectories to classify each measurement by hemisphere, as well as continental or ocean. For air passing over ocean before sampling, TGM concentrations are 10 % higher in air coming from the Northern Hemisphere (1.45 ng m −3 ) than from the Southern Hemisphere (1.32 ng m −3 ). Air from the South American continent also carries higher TGM (1.43 ng m −3 ) than air from the South Atlantic Ocean, with most of these trajectories occurring in August and September. Biomass burning in Brazil peaks in the same months and likely contributes significantly to elevated concentrations seen in Nickerie. We also compare the observed seasonal cycle to two atmospheric mercury chemistry and transport models (GRAHM and GEOS-Chem). Both models simulate transition between northern and southern hemispheric air, thus capturing the seasonal cycle; however the models overestimate the TGM concentrations during months when Nickerie samples Northern Hemisphere air. It is difficult to determine whether the models' sources or sinks in the Northern Hemisphere tropics are responsible.

Atmospheric mercury in the Southern Hemisphere tropics: seasonal and diurnal variations and influence of inter-hemispheric transport

“…Towards the equator, the existence of the Intertropical Convergence Zone (ITCZ) and the associated upward/poleward movement of the Hadley circulation leads to reduced tropospheric mixing across the atmospheric or chemical equator (Bowman and Cohen, 1997;Hamilton et al, 2008;Holmes and Prather, 2017) and hence a broad, hemispheric gradient of GEM concentrations (Slemr et al, 1985;Sprovieri et al, 2016). Stationary observations of GEM within the tropics are rare but those that are available report significant changes in concentration as source regions shift across hemispheres with the drift of the atmospheric equator (Müller et al, 2012;Wang et al, 2014). The tropics also represent an important region for mercury cycling as they are home to around 40 % of the world's population, including over 50 % of people under the age of 15, a group at greater risk of adverse effects due to mercury exposure during early development (Bose-O'Reilly et al, 2010).…”

“…Characterisation of background GEM in the tropics and Southern Hemisphere (SH) has been hindered by a lack of observations and is based largely on intermittent ship voyages (Soerensen et al, , 2014, along with a few longterm stationary records in South America, Africa, Antarctica, and islands in the Indian and eastern Pacific oceans (Sheu et al, 2010;Müller et al, 2012;Wang et al, 2014;Angot et al, 2014Angot et al, , 2016Slemr et al, 2015). A recent comparison of interannual records from four mercury monitoring stations spanning a latitude range of 34-72 • S, of which the longestrunning spans 7 years, suggests that background GEM concentrations in the SH are between 0.85 and 1.05 ng m −3 .…”

Four years (2011–2015) of total gaseous mercury measurements from the Cape Verde Atmospheric Observatory

“…The site at Nieuw Nickerie experiences 10 % higher concentrations in the air arriving from the north compared to the south (Müller et al, 2012) and is additionally impacted by emissions from biomass burning and gold mining from South America . Comparisons to ship-borne field campaigns in the Atlantic made between 1977 and 2001 show that the data from CVO are more comparable with southern Atlantic conditions than the northern Atlantic.…”

Atmospheric mercury in the southern hemisphere tropics: seasonal and diurnal variations and influence of inter-hemispheric transport

“…Towards the equator, the existence of the Intertropical Convergence Zone (ITCZ) and the associated upward/poleward movement of the Hadley circulation leads to reduced tropospheric mixing across the atmospheric or chemical equator (Bowman and Cohen, 1997;Hamilton et al, 2008;Holmes and Prather, 2017) and hence a broad, hemispheric gradient of GEM concentrations (Slemr et al, 1985;Sprovieri et al, 2016). Stationary observations of GEM within the tropics are rare but those that are available report significant changes in concentration as source regions shift across hemispheres with the drift of the atmospheric equator (Müller et al, 2012;Wang et al, 2014). The tropics also represent an important region for mercury cycling as they are home to around 40 % of the world's population, including over 50 % of people under the age of 15, a group at greater risk of adverse effects due to mercury exposure during early development (Bose-O'Reilly et al, 2010).…”

“…Characterisation of background GEM in the tropics and Southern Hemisphere (SH) has been hindered by a lack of observations and is based largely on intermittent ship voyages (Soerensen et al, , 2014, along with a few longterm stationary records in South America, Africa, Antarctica, and islands in the Indian and eastern Pacific oceans (Sheu et al, 2010;Müller et al, 2012;Wang et al, 2014;Angot et al, 2014Angot et al, , 2016Slemr et al, 2015). A recent comparison of interannual records from four mercury monitoring stations spanning a latitude range of 34-72 • S, of which the longestrunning spans 7 years, suggests that background GEM concentrations in the SH are between 0.85 and 1.05 ng m −3 .…”