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Abstract:
Gaseous elemental mercury (GEM) and Rn-222, 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 2009 altogether 59 events with high Rn-222 concentrations were identified. GEM correlated with Rn-222 in 41 of the events and was constant during the remaining events without significant correlation. The average GEM/Rn-222 emission ratio of all events was -0.0047 +/- 0.0054 pg mBq(-1), with +/- 0.0054 being the standard error of the average. With an emission rate of 1.1 Rn-222 atoms cm(-2) s(-1) and a correction for the transport duration, this emission ratio corresponds to a radon calibrated flux of about -0.53 +/- 0.62 ng m(-2) h(-1) which is statistically not distinguishable from zero. With wet deposition, which is not included in this estimate, the terrestrial surface of southern Africa appears to be a net mercury sink.
