HR: 13:55h
AN: V12E-02    [PDF]
TI: Aerosol Evolution Within a Low-Temperature Volcanic Plume
AU: * Pfeffer, M A
EM: pfeffer@dkrz.de
AF: Max Planck Institute for Meteorology, Bundestrasse 55, Hamburg, 20146 Germany
AU: Rietmeijer, F J
EM: fransjmr@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM 87131 United States
AU: Brearley, A J
EM: brearley@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM 87131 United States
AU: Fischer, T P
EM: fischer@unm.edu
AF: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM 87131 United States
AB: In order to investigate the early evolution of aerosols within a volcanic plume, atmospheric samples were collected at Poas, a persistently degassing volcano in Costa Rica. Chemical bulk compositions and morphologies of the collected aerosols were examined using transmission electron microscopy. Aerosol morphologies correlate with distinctions in composition and with sampling location. A bimodal size distribution of aerosols is observed at all sampling locations. The small aerosols exist in clusters of semi-spherical bodies averaging 35nm across, characteristic of homogeneously nucleated aerosols. The large aerosols are solid and/or liquid, with the solid aerosols averaging 150nm across, characteristic of primary aerosols. The large liquid aerosols have more complex bulk chemistry than the small homogeneously nucleated aerosols, both size and composition suggesting they condensed on already existing aerosols. Both size modes of aerosols are 300nm larger 280m distant from source, indicating that coagulation commences immediately and occurs uniformly for both modes of aerosols. Aerosol compositions were compared with predictions of an equilibrium model assuming homogeneous nucleation of aerosols generated by mixing the $92\deg$C volcanic gases with ambient temperature air. The collected aerosols have different and more complex compositions than the model predicts to be stable in the plume. We suggest that heterogeneous nucleation and coagulation are important processes in the first seconds of plume travel and these processes, as well as the inclusion of airborne, locally-produced mineral dust must be considered in an accurate model of plume evolution.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0370 Volcanic effects (8409)
DE: 8409 Atmospheric effects (0370)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting