Abstract
Abstract. Gaseous elemental mercury (GEM) and 222Rn, a radioactive gas of primarily terrestrial origin with a half-life of 3.8 days, have been measured simultaneously at Cape Point, South Africa, since March 2007. Between March 2007 and December 2011, altogether 191 events with high 222Rn concentrations were identified. GEM correlated with 222Rn in 94 of the events and was constant during almost all the remaining events without significant correlation. The average GEM / 222Rn flux ratio of all events including the non-significant ones was −0.0001 with a standard error of ±0.0030 pg mBq−1. Weighted with the event duration, the average GEM / 222Rn flux ratio was −0.0048 ± 0.0011 pg mBq−1. With an emission rate of 1.1 222Rn atoms cm−2 s−1 and a correction for the transport time, this flux ratio corresponds to a radon-calibrated flux of about −0.54 ng GEM m−2 h−1 with a standard error of ±0.13 ng GEM m−2 h−1 (n = 191). With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa seems to be a net mercury sink of about −1.55 ng m−2 h−1. The additional contribution of an unknown but presumably significant deposition of reactive gaseous mercury would further increase this sink.
Highlights
Including the non-significant ones was −0.0001 with a standard error of ±0.0030 pg mBq−1
The flux can be bi-directional depending on the mercury concentration in Mercury poses a serious environmental issue because of its transformation to methyl mercury, which is a potent toxin to humans and animals (Mergler et al, 2007; Scheuhammer et al, 2007)
Under the prevailing atmospheric conditions at Cape Point, we assume that reactive gaseous mercury (RGM) will be adsorbed by the inlet tubing and the aerosol filter and that the measured atmospheric mercury concentration represents exclusively gaseous elemental mercury (GEM) (Brunke et al, 2010)
Summary
The Cape Point station (34◦21 S, 18◦29 E) is part of the World Meteorological Organization’s (WMO) Global Atmosphere Watch (GAW) network. Gaseous mercury concentrations had been measured intermittently (about 200 samples per year) since September 1995 until December 2004 (Slemr et al, 2008) and have been continuously with a resolution of 15 min since March 2007 (Brunke et al, 2010). Under the prevailing atmospheric conditions at Cape Point (higher temperature and air humidity, in addition to hygroscopic sea salt aerosols), we assume that reactive gaseous mercury (RGM) will be adsorbed by the inlet tubing and the aerosol filter and that the measured atmospheric mercury concentration represents exclusively gaseous elemental mercury (GEM) (Brunke et al, 2010). Decay products newly formed under controlled conditions in the instrument delay tank are retained by a second filter Their alpha radiation is determined by a zinc sulfide scintillator.
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