Mercury in the atmosphere and in rainwater at Cape Point, South Africa

Abstract

Mercury measurements were concurrently made in air (Gaseous Elemental Mercury, i.e. GEM) as well as in precipitation samples (Total mercury, i.e. TotHg) over a seven year period (2007-2013) at Cape Point, South Africa, during the rainy seasons (May-October). Eighty-five rain events, almost exclusively associated with cold fronts, have been identified of which 75% reached the Cape Point observatory directly across the Atlantic Ocean from the south, while 19% moved in to the measuring site via the Cape Town metropolitan region. In statistic terms the GEM, TotHg, CO and ²²²Rn levels within the urban-marine events do not differ from those seen in the marine rain episodes. Over the 2007-2013 period, the May till Oct averages for GEM ranged from 0.913 ng m^-3 to 1.108 ng m^-3, while TotHg concentrations ranged from 0.03 to 52.5 ng L^-1 (overall average: 9.91 ng L^-1). A positive correlation (R² = 0.49, n = 7) has been found between the average annual (May till October) GEM concentrations in air and TotHg concentration in rainwater suggesting a close relationship between the two species. The wetter years are normally associated with higher GEM and TotHg levels. Both GEM and TotHg annual means correlate positively with total annual (May till October) rain depths. If one or two outlier years are removed from the data set, the R² values increase from 0.23 to 0.10 for GEM and TotHg to 0.97 (n = 5) and 0.89 (n = 5), respectively. The relationship between annual mean GEM and annual precipitation depth also holds for the period 1996-2004 (R² = 0.6, n = 8) when GEM was measured manually (low resolution data). A positive correlation was also seen between annual average GEM concentrations and the El Nifio Southern Oscillation (ENSO) Index (SOI), for the 1996-2004 period (R² = 0.7, n = 8). For the 2007-2013 periods this relationship was also positive but less pronounced. The relationship between annual precipitation depth and annual SOI suggests that the inter-annual variations of GEM (Hg0) concentration might be caused by large-scale meteorological processes. (C) 2015 Elsevier Ltd. All rights reserved

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

“…Within tropical regions, wet deposition has been shown to be a significant pathway for mercury from the atmosphere to both oceanic and terrestrial ecosystems, even in relatively low-mercury air and despite the low solubility of mercury in its elemental form (Fostier et al, 2000;Costa et al, 2012;Hansen and Gay, 2013;Soerensen et al, 2014;Shanley et al, 2015). Mercury "rainout" -or the tendency for mercury rainwater loading to decrease with increasing precipitation -has also been demonstrated in Mercury Deposition Network (MDN) data in North America (Glass and Sorensen, 1999;Prestbo and Gay, 2009) and positive correlations between GEM (TGM) and rainwater mercury have been reported in MDN data (GEM; Cole et al, 2014) and at Cape Point, South Africa (TGM; Brunke et al, 2016). Re-emission of any deposited mercury is likely to be inhibited throughout the wet season, as it has been shown that GEM emission from background mercury soils is suppressed when the soils are saturated (Briggs and Gustin, 2013).…”

Atmospheric mercury deposition over the land surfaces and the associated uncertainties in observations and simulations: a critical review

“…Therefore, here we only briefly introduce the spatial distribution of forest Hg deposition. South America was estimated to bear the highest litterfall Hg deposition (65.8 ± 57.5 µg m −2 yr −1 ) around the world (Teixeira et al, 2012(Teixeira et al, , 2017Buch et al, 2015;Fostier et al, 2015;Fragoso et al, 2018;Shen et al, 2019). There have been numerous forest Hg deposition studies in the recent decade in East Asia with the second highest average litterfall Hg deposition flux (35.5 ± 27.7 µg m −2 yr −1 ) (Wan et al, 2009;Wang et al, 2009;Fu et al, 2010aFu et al, , b, 2016aGong et al, 2014;Luo et al, 2016;Ma et al, 2015Ma et al, , 2016Han et al, 2016;Wang et al, 2016b;Zhou et al, 2016Zhou et al, , 2017.…”

El Niño–Southern Oscillation influence on tropospheric mercury concentrations

“…Brunke et al [] noticed that the annual average mercury concentrations in the atmosphere and in rainwater at Cape Point, South Africa, correlate with annual precipitation depth which in turn is also influenced by ENSO in southern Africa. This finding prompted us to analyze several atmospheric mercury data sets in detail, each of which encompasses more than 8 years of measurements.…”

“…Because biomass burning is one of the major sources of atmospheric CO, CH 4 , CH 3 Cl, and many other trace gases and aerosols [Andreae and Merlet, 2001], the observed interannual variations of many of these gases could be shown to be driven by ENSO [e.g., Wang et al, 2004;Simmonds et al, 2005;Logan et al, 2008;Chandra et al, 2009;Voulgarakis et al, 2010;Inness et al, 2015]. Brunke et al [2016] noticed that the annual average mercury concentrations in the atmosphere and in rainwater at Cape Point, South Africa, correlate with annual precipitation depth which in turn is also influenced by ENSO in southern Africa. This finding prompted us to analyze several atmospheric mercury data sets in detail, each of which encompasses more than 8 years of measurements.…”