However, we have examples of Tasmanian fires from the Bass Strait islands or the Tasmanian mainland that impinge on Cape Grim and do not show the usual urban markers such as HFC134a (CH2FCF3). These plumes affecting Cape Grim are likely to be due to fires only. In these instances there is no evidence of any CCl4 enhancement in the bushfire plumes. We conclude that bushfires are not a significant source of CCl4 emissions. These examples are shown in Figures 8 and 9. Although not obvious from the data, there is the suggestion that CCl4 levels in the fire plumes are slightly lower than baseline, indicating some CCl4 destruction in the fire. This will be further investigated later for a wider range of fires at Cape Grim. Figure 8. Figure 9. Trace gas Trace gas enhancements enhancements in a in a ‘pure’ ‘pure’ bushfire plume bushfire plume (i.e. a plume seen at Cape that is not Grim. On 19 contaminated March 2008 with urban air) (purple vertical seen at Cape column), there Grim, is a large Tasmania, biomass 26–27 burning February 1995 episode that (purple vertical shows no column). The enhancement large biomass in CCl4, but a burning very large episode (27 enhancement February) in CO (approx shows no 3000 ppb). enhancement According to in CCl4, but a back-trajectory very large information enhancement this large in CO (approx. event has not 1000 ppb). been This biomass influenced by burning event Melbourne was the result (urban) air. of a local Earlier grass fire. In biomass contrast, on burning 25 February episodes 1995 (grey March) vertical have been column) there influenced by is a Melbourne Melbourne air pollution event and therefore that results in show a small elevated CCl4, enhancement CFC-12, CH4 in CCl4. and CO
However, we have examples of Tasmanian fires from the Bass Strait islands or the Tasmanian mainland that impinge on Cape Grim and do not show the usual urban markers such as HFC134a (CH2FCF3). These plumes affecting Cape Grim are likely to be due to fires only. In these instances there is no evidence of any CCl4 enhancement in the bushfire plumes. We conclude that bushfires are not a significant source of CCl4 emissions. These examples are shown in Figures 8 and 9. Although not obvious from the data, there is the suggestion that CCl4 levels in the fire plumes are slightly lower than baseline, indicating some CCl4 destruction in the fire. This will be further investigated later for a wider range of fires at Cape Grim. Figure 8. Trace gas enhancements in a ‘pure’ bushfire plume (i.e. a plume that is not contaminated with urban air) seen at Cape Grim, Tasmania, 26–27 February 1995 (purple vertical column). The large biomass burning episode (27 February) shows no enhancement in CCl4, but a very large enhancement in CO (approx. 1000 ppb). This biomass burning event was the result of a local grass fire. In contrast, on 25 February 1995 (grey vertical column) there is a Melbourne pollution event that results in elevated CCl4, CFC-12, CH4 and CO Figure 9. Trace gas enhancements in a ‘pure’ bushfire plume seen at Cape Grim. On 19 March 2008 (purple vertical column), there is a large biomass burning episode that shows no enhancement in CCl4, but a very large enhancement in CO (approx 3000 ppb). According to back-trajectory information this large event has not been influenced by Melbourne (urban) air. Earlier biomass burning episodes March) have been influenced by Melbourne air and therefore show a small enhancement in CCl4.
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