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 degreesS, 18 degreesE). 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 * 10(3) kt yr(-1) (range 400 - 700 * 10(3) 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(-1)). Similarly, based on a CO2 emission from biomass burning of 3460 * 103 ktC yr(-1) (range 3000 - 6200 ktC yr(-1)), 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(-1)), 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.