Enhancement of the volcanogenic "bromine explosion" via reactive nitrogen chemistry (Kīlauea volcano, Hawai'i)

Abstract. Since the first detection of bromine monoxide in volcanic plumes attention has focused on the atmospheric synthesis and impact of volcanogenic reactive halogens. We report here new measurements of BrO in the volcanic plume emitted from Kīlauea volcano – the first time reactive halogens have been observed in emissions from a hotspot volcano. Observations were carried out by ground-based Differential Optical Absorption Spectroscopy in 2007 and 2008 at Pu'u'O'o crater, and at the 2008 magmatic vent that opened within Halema'uma'u crater. BrO was readily detected in the Halema'uma'u plume (average column amount of 3×1015 molec cm⁻²) and its abundance was strongly correlated with that of SO₂. However, anticorrelation between NO₂ and SO₂ (and BrO) abundances in the same plume strongly suggest an active role of NO_x in reactive halogen chemistry. The calculated SO₂/BrO molar ratio of ~1600 is comparable to observations at other volcanoes, although the BrO mixing ratio is roughly double that observed elsewhere. While BrO was not observed in the Pu'u'O'o plume this was probably merely a result of the detection limit of our measurements and based on understanding of the Summit and East Rift magmatic system we expect reactive halogens to be formed also in the Pu'u'O'o emissions. If this is correct then based on the long term SO₂ flux from Pu'u'O'o we calculate that Kīlauea emits ~480 Mg yr⁻¹ of reactive bromine and may thus represent an important source to the tropical Pacific troposphere.