HR: 0800h
AN: A21C-0756    [Abstracts]
TI: Experimentation and modelling of mineral aerosol dissolution as source of transition metals in cloud droplets
AU: * Desboeufs, K
EM: desboeufs@lisa.univ-paris12.fr
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AU: Sofikitis, A
EM: sofikitis@lisa.univ-paris12.fr
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AU: Velay, J
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AU: Losno, R
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AU: Dulac, F
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AU: Dulac, F
AF: LSCE, CEA-CNRS, CEA Saclay 709, Gif sur Yvette, 91191 France
AU: Colin, J
AF: LISA, Facult‚ des sciences 61 av. du General de Gaulle, Creteil, 94010 France
AB: Even at nano-molar concentrations, transition metals (TMI) could play an important role in the radical chemistry of the atmospheric liquid phase. For instance, cloud chemistry model calculations suggest that depletion of HOx by reactions between TMI and HO2/O2- radicals significantly slows down O3 production in polluted clouds. TMI are transferred into the liquid phase from aerosol particles by dissolution processes which can be a slow reaction. The dissolution kinetic of the solid phase thus competes with chemical kinetics in the homogeneous aqueous phase. It is therefore of importance to consider the evolution of TMI concentrations into cloud droplets in order to quantify the atmospheric impact of aerosols on the aqueous chemistry. Mineral particles including soil-derived particles and fly-ash are important sources of TMI in the troposphere.In order to parameterize the dissolution kinetic and concentrations of TMI from mineral particles into cloud droplets, we have conducted experimental laboratory simulations which mimic particles/water interactions occurring into droplets. These simulations were carried out in an open-flow reactor for typical atmospheric conditions (pH, ionic strength.). Data on TMI dissolution kinetic are provided for two generic kinds of mineral matrices from anthropogenic and natural sources: alumino-silicated and carbonaceous particles (dust, fly-ash, or urban particles). The concentrations of TMI released depend on pH, matrix type and particle-water contact time. The metals coming from carbonaceous particles are adsorbed impurities or salts and are very soluble with dissolution hardly dependent on pH. On the opposite, the metals dissolved from alumino-silicated particles are less soluble, notably the ones constitutive of the matrix network (Fe, Mn), and their dissolution is highly influenced by the pH. However, at a given pH, the results on the kinetic of dissolution emphasize that whatever the matrix, the TMI dissolution rates decrease with the contact time following a double first order kinetic. The kinetic constant of dissolution is determined for each metal from each particle type and at various pH. It appears that these constants are also directly related to the mineral matrix types. From these observations, the metals dissolution is parameterized as a function of particle-water contact time and particle composition. This parameterization could be included in cloud chemistry models.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0335 Ion chemistry of the atmosphere (2419, 2427)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting