Emissions of mercury in southern Africa derived from long-term observations at Cape Point, South Africa

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, Hg 0 ), GEM/CO 2 , GEM/CH 4 , CO/CO 2 , CH 4 /CO 2 , and CH 4 /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/CO 2 , GEM/CH 4 , CO/CO 2 , CH 4 /CO 2 , 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/CO 2 , CH 4 /CO 2 , and CH 4 /CO emission ratios agree within the combined uncertainties of the observations and emissions with the ratios calculated from EDGAR (version 4.2) CO 2 , CO, and CH 4 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/CO 2 , and GEM/CH 4 emission ratios and the annual mean CO, CO 2 , and CH 4 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)(2008)(2009) as well as better data on the speciation of the total mercury emissions in South Africa.

Correlation slopes of GEM / CO, GEM / CO<sub>2</sub>, and GEM / CH<sub>4</sub> and estimated mercury emissions in China, South Asia, the Indochinese Peninsula, and Central Asia derived from observations in northwestern and southwestern China

“…The geometric means of the CO / CO 2 correlation slopes for mainland China, South Asia, and Central Asia were 29.0 ± 20.8 (1 SD, n = 43), 22.5 ± 20.7 (1 SD, n = 8), and 16.8 ± 8.4 ppb ppm −1 (1 SD, n = 8) , respectively. The observed correlation slopes for CH 4 / CO, CH 4 / CO 2 , and CO / CO 2 in the studied regions were higher than that obtained for South Africa (Brunke et al, 2012). Note that observed CH 4 / CO and CH 4 / CO 2 correlation slopes were lower than anthropogenic emission ratios of CH 4 / CO and CH 4 / CO 2 , while observed CO / CO 2 correlation slopes were consistent with anthropogenic emission ratios of CO to CO 2 (with the exception of South Asia, Table 1 and Table 2).…”

“…The GEM / CO, GEM / CO 2 , and GEM / CH 4 correlation slopes in Asian were higher than those observed in other regions. For example, the GEM / CO ratios in Europe, South Africa, and North America were in the range of 0.3-5.0 pg m −3 ppb −1 (Jaffe et al, 2005;Slemr et al, 2006;Brunke et al, 2012). For GEM / CO 2 ratios, previous studies reported a mean of 184 pg m −3 ppm −1 for the northeastern USA and 63 pg m −3 ppm −1 for South Africa (Lee et al, 2001;Brunke et al, 2012).…”

“…Asia, Europe, and South Africa (Jaffe et al, 2005;Slemr et al, 2006;Brunke et al, 2012). Such a measurement-based method complements the regional emission inventories estimated by means of conventional statistical approaches.…”

“…This method was developed and first utilized for estimating Hg emissions in Asia using the correlation of GEM to CO during Asian outflow events (Jaffe et al, 2005). Subsequently, correlation slopes between GEM and other trace gases such as CH 4 , CO 2 , and halocarbons were also calculated (Slemr et al, 2006;Brunke et al, 2012). These methods are based on assumptions of no chemical and physical losses of air pollutants, as well as constant emission ratios and constant background of air pollutants during atmospheric transport events (Jaffe et al, 2005).…”

<sup>222</sup>Rn-calibrated mercury fluxes from terrestrial surface of southern Africa

“…The events can extend up to 7 days, but most of them last 2-4 days. Their duration is thus substantially longer than that of the depletion events or the typical pollution plumes observed at Cape Point, which generally last only several hours (Brunke et al, 2010(Brunke et al, , 2012. Using time series and scatter plots, this difference allows us to discriminate against the depletion events, the anthropogenic emissions and emission from biomass burning.…”