Gaseous mercury emissions from a fire in the Cape Peninsula, South Africa, during January 2000

During mid-January 2000 the plume from a fire, which destroyed 9000 ha of mixed vegetation in the southern part of the Cape Peninsula, passed over the Cape Point Global Atmosphere Watch station (34°S, 18°E). The smoke plume was characterized by a CO/CO2 emission ratio (ER) of 0.0548 ± 0.0018 mol/mol, typical for biomass burning. Measurements of total gaseous mercury (TGM) made during this episode provided Hg/CO and Hg/CO2 emission ratios of(2.10 ± 0.21) * 10-7 and (1.19 ± 0.30) * 10-8 mol/mol, respectively. Based on the presently accepted CO source estimate for biomass burning of 621 * 103 kt yr-1 (range 400 - 700 * 103 kt yr-1), the ER(Hg/CO) suggests that the global mercury emission from biomass burning amounts to approximately 0.93 kt annually (range 0.51 - 1.14 kt yr-l). Similarly, based on a CO2 emission from biomass burning of 3460 * 103 ktC yr-1 (range 3000 - 6200 ktC yr-l), the ER(Hg/CO2) suggests that the global mercury emission from biomass burning amounts to approximately 0.59 kt annually (range 0.38 - 1.33 kt yr-l), in good agreement with the emission estimated from the ER(Hg/CO). If supported by measurements from fires in other regions, mercury emissions from biomass burning of the order of 1 kt yr-1 could represent one of the major, hitherto neglected, sources of atmospheric mercury.