Abstract
Abstract. Mercury emissions in South Africa have so far been estimated only by a bottom-up approach from activities and emission factors for different processes. In this paper we derive GEM/CO (GEM being gaseous elemental mercury, Hg0), GEM/CO2, GEM/CH4, CO/CO2, CH4/CO2, and CH4/CO emission ratios from plumes observed during long-term monitoring of these species at Cape Point between March 2007 and December 2009. The average observed GEM/CO, GEM/CO2, GEM/CH4, CO/CO2, CH4/CO2, and CH4/CO emission ratios were 2.40 ± 2.65 pg m−3 ppb−1 (n = 47), 62.7 ± 80.2 pg m−3 ppm−1 (n = 44), 3.61 ± 4.66 pg m−3 ppb−1 (n = 46), 35.6 ± 25.4 ppb ppm−1 (n = 52), 20.2 ± 15.5 ppb ppm−1 (n = 48), and 0.876 ± 1.106 ppb ppb−1 (n = 42), respectively. The observed CO/CO2, CH4/CO2, and CH4/CO emission ratios agree within the combined uncertainties of the observations and emissions with the ratios calculated from EDGAR (version 4.2) CO2, CO, and CH4 inventories for South Africa and southern Africa (South Africa, Lesotho, Swaziland, Namibia, Botswana, Zimbabwe, and Mozambique) in 2007 and 2008 (inventories for 2009 are not available yet). Total elemental mercury emission of 13.1, 15.2, and 16.1 t Hg yr−1 are estimated independently using the GEM/CO, GEM/CO2, and GEM/CH4 emission ratios and the annual mean CO, CO2, and CH4 emissions, respectively, of South Africa in 2007 and 2008. The average of these independent estimates of 14.8 t GEM yr−1 is much less than the total emission of 257 t Hg yr−1 shown by older inventories which are now considered to be wrong. Considering the uncertainties of our emission estimate, of the emission inventories, and the fact that emission of GEM represents 50–78 % of all mercury emissions, our estimate is comparable to the currently cited GEM emissions in 2004 and somewhat smaller than emissions in 2006. A further increase of mercury emissions due to increasing electricity consumption will lead to a more pronounced difference. A quantitative assessment of the difference and its significance, however, will require emission inventories for the years of observations (2007–2009) as well as better data on the speciation of the total mercury emissions in South Africa.
Highlights
Mercury emissions to the atmosphere are of global importance because of its long range transport, deposition and partial transformation to highly neurotoxic methyl mercury
A small additional uncertainty originates from using the average annual emissions for 2007 and 2008 while the observations cover 2009 as well for which the emissions are not available yet. Taking all these uncertainties into account we conclude that the CO/CO2, CH4/CO2 and CH4/CO emission ratios observed at Cape Point reproduce reasonably well the emission ratios for South Africa and southern Africa calculated from the EDGAR inventory
Sixty seven pollution events have been identified over the period from March 2007 till December 2009 and analysed for the following emission ratios: gaseous elemental mercury (GEM)/CO, GEM/CO2, GEM/CH4, CO/CO2, CH4/CO2, and CH4/CO
Summary
Mercury emissions to the atmosphere are of global importance because of its long range transport, deposition and partial transformation to highly neurotoxic methyl mercury. Nriagu and Pacyna, 1988; Nriagu, 1989; Pirrone et al, 1996, 1998, 2010; Pacyna et al, 2002, 2003, 2006, 2010; Streets et al, 2005, 2009) Despite all these efforts the emission estimates are still quite uncertain, especially those related to natural sources and anthropogenic emissions in rapidly developing countries in East. In emission inventories for 1995 and 2000 South Africa and especially its provinces Gauteng and Mpumalanga were supposed to represent the region with the highest mercury emission density within the southern hemisphere (Pacyna et al 2003; Wilson et al, 2006). Selin et al, 2007; 2008; Strode et al, 2007) but the uncertainty of these constraints is seldom smaller than that of the emission inventories Such global constraints do not provide much information about regional emission densities. In addition the GEM/CO, GEM/CO2, and GEM/CH4 emission ratios for plumes which according to the backward trajectories originate from the Gauteng and Mpumalanga provinces are compared with emission ratios from other regions
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