| Summary: | We report measurements of Hg, SO₂, and halogens (HCI, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gasceous SO₂ and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO₂ and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m⁻³. Hg/SO₂ mass ratios measured with the real-time instruments ranged from 1.1 x 10⁻⁷ to 3.5 x 10⁻⁵ (mean 2 x 10⁻⁵). Total gaseous mercury (TGM) concentrations measured by gold trap ranged from 100 to 225 ng m⁻³. Reactive gaseous mercury accounted for 1% of TGM, while particulate mercury was 5% of the TGM. Field measurements of Masaya's SO₂ flux, combined with the Hg/SO₂ ratio, indicate a Hg flux from Masaya of 7.2 Mg a⁻¹. At Masaya's low temperature fumaroles, Hg/CO₂ mass ratios were consistently around 2 x 10⁻⁸, lower than observed in the main vent (Hg/CO₂ ~ 10⁻⁷). Low-temperature fumarole Hg fluxes from Masaya are insignificant (~ 150 g a⁻¹). Ratios of S, C and halogen species were also measured at Masaya and Telica volcanoes. CO₂/SO₂ ratios at Masaya ranged from 2.8 to 3.9, comparable to previously published values. At Masaya molar Br/SO₂ was 3 x 10⁻⁴ and I/SO₂ was 2 x 10⁻⁵, suggesting fluxes of 0.2-0.5 Mg Hbr d⁻¹ and 0.03-0.05 Mg HI d⁻¹. At Telica the Br/SO₂ ratio was also 3 x 10⁻⁴ and the I/SO₂ ratio was 5.8 x 10⁻⁵, with corresponding fluxes of 0.2 Mg HBr d⁻¹ and 0.06 Mg HI d⁻¹. Gases at both volcanoes are enriched in I relative to Br and CI, compared to gases from volcanoes elsewhere.
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