Abstract
Tropospheric sections of flights with the CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrumented Container) observatory from May 2005 until June 2013, are investigated for the occurrence of plumes with elevated Hg concentrations. Additional information on CO, CO2, CH4, NOy, O3, hydrocarbons, halocarbons, acetone and acetonitrile enable us to attribute the plumes to biomass burning, urban/industrial sources or a mixture of both. Altogether, 98 pollution plumes with elevated Hg concentrations and CO mixing ratios were encountered, and the Hg/CO emission ratios for 49 of them could be calculated. Most of the plumes were found over East Asia, in the African equatorial region, over South America and over Pakistan and India. The plumes encountered over equatorial Africa and over South America originate predominantly from biomass burning, as evidenced by the low Hg/CO emission ratios and elevated mixing ratios of acetonitrile, CH3Cl and particle concentrations. The backward trajectories point to the regions around the Rift Valley and the Amazon Basin, with its outskirts, as the source areas. The plumes encountered over East Asia and over Pakistan and India are predominantly of urban/industrial origin, sometimes mixed with products of biomass/biofuel burning. Backward trajectories point mostly to source areas in China and northern India. The Hg/CO2 and Hg/CH4 emission ratios for several plumes are also presented and discussed.
Highlights
Mercury (Hg) is emitted by natural and anthropogenic processes, and because of its rather long atmospheric lifetime of one year, it can be transported over long distances [1,2]
We note that even if gaseous oxidized mercury (GOM) concentrations in the upper troposphere represent more than 1% or less of total gaseous mercury concentrations typically found in the boundary layer [36,37], its non-quantitative transmission by our inlet system would not substantially influence the results presented in this paper
Applying these criteria to the Hg/CO emission ratios shown in Figure 3 leads to the conclusion that the plumes encountered during the flights to South America and equatorial Africa originate predominantly from biomass burning, whereas the plumes observed over East
Summary
Mercury (Hg) is emitted by natural and anthropogenic processes, and because of its rather long atmospheric lifetime of one year, it can be transported over long distances [1,2]. An artificial tracer, such as SF6, is emitted in an area under investigation and the emission of the target substance is calculated from the known emission of the artificial tracer and the correlations of the target substance concentrations with those of the tracer. Both techniques have been successfully used to determine emissions of CO and NOy of a middle-sized city [18], but they can hardly be scaled up to larger areas. Correlations of Hg with CO, CO2 and CH4 provide Hg/CO, Hg/CO2 and Hg/CH4 emission ratios, which may help to constrain the estimates of mercury emissions using the CO, CO2 and CH4 emission inventories [21]
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