Photoelectric charging of ultrafine volcanic aerosols: Detection of Cu(I) as a tracer of chlorides in magmatic gases

Abstract

Volcanic gases contain ultrafine aerosol particles in the nanometer size range; typical concentrations are 105 to 106 cm−3. Photoelectric charging of particles (PCP) is an in situ method for the material specific detection of very small particles in a gas. Field studies at degassing lava flows of Mount Etna, Sicily, and Kilauea, Hawaii, show that the chemistry of the ultrafine aerosols depends strongly on the degassing state of the lava. Heating of a relatively undegassed lava sample in the laboratory reveals the chemical nature of the particles that form by nucleation and condensation in the cooling gas. In the initial stages of degassing, the particles are mainly NaCl and KCl nanocrystals that contain iron oxide and copper chloride. Cu is in the monovalent state, which is stable even in an oxidizing environment due to a redox mechanism with the Fe ions. The fraction of Cu(I) in the aerosols is determined by PCP. The evolution of the Cu(I) fraction is considered an effective tracer of chlorides in the magmatic gases and thereby of magma degassing. The PCP technique allows a fingerprint to be obtained of the magmatic gas by an aerosol measurement in the diluted plume.

Halogens and trace metal emissions from the ongoing 2008 summit eruption of Kīlauea volcano, Hawai`i

“…2). These differences are consistent with the proposed role of halogens in terms of metal volatilisation and transportation in volcanic plumes (Murata, 1960;Symonds et al, 1987Symonds et al, , 1992Ammann et al, 1993).…”

“…However, recent measurements (made using similar analytical techniques) by Moune et al (2010) from Masaya volcano, Nicaragua, another basaltic system, yielded metal/sulphur ratios that were at least an order of magnitude larger for all elements measured, compared to those reported here. Studies based on limited measurements (e.g., spectroscopic measurements of CuCl(g) in K ılauea's plume by Murata, 1960), laboratory experiments (Ammann et al, 1993) and thermodynamic modelling (Symonds et al, 1987(Symonds et al, , 1992 suggest that many metals are primarily volatilised from the magma as chloride species. Moune et al (2010) did not report simultaneous measurements of gas phase halogen halides in Masaya's plume but HCl/SO 2 ratios tend to be an order of magnitude higher at Masaya than at K ılauea (e.g., Pyle and Mather, 2009) consistent with the suggestion that low halogen levels are responsible for the relatively metal-poor nature of the emissions from Hawaii.…”

“…Contrasting patterns of halogen emission in different tectonic settings may also lead to differences in volcanic trace-metal emissions, as halogens are thought to play an important, if poorly understood, role in metal degassing (Murata, 1960;Symonds et al, 1987Symonds et al, , 1992Ammann et al, 1993;Aiuppa et al, 2009). Therefore, understanding trace-metal behaviour in K ılauea's plumes may provide important insights into the factors that control volcanic trace-metal degassing.…”

The uptake of halogen (HF, HCl, HBr and HI) and nitric (HNO3) acids into acidic sulphate particles in quiescent volcanic plumes

“…and Burtscher et al, 1990;Ammann et al, 1993; Toutain et al, 1995; Martin et al, 2008; Moune et 94 al., 2010) show a range of compositions indicating that internal mixing is neither negligible nor 95 complete. Thus, while local equilibrium may be established between gases and particles over 96 timescales as short as a few seconds (Wexler and Seinfeld, 1992), the overall gas and particle 97 composition may remain out of equilibrium.…”

“…Due to the extreme hygroscopicity of H 2 SO 4 , along with the high abundances of 91 gas-phase H 2 SO 4 and H 2 O, binary homogenous nucleation of H 2 SO 4 and H 2 O may occur, in addition 92 to the heterogeneous nucleation of H 2 SO 4 onto metal salts. Single particle analyses (e.g., Ammann 93and Burtscher et al, 1990;Ammann et al, 1993; Toutain et al, 1995; Martin et al, 2008; Moune et 94 al., 2010) show a range of compositions indicating that internal mixing is neither negligible nor 95 complete. Thus, while local equilibrium may be established between gases and particles over 96 timescales as short as a few seconds (Wexler and Seinfeld, 1992), the overall gas and particle 97 composition may remain out of equilibrium.…”