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Electron microscope studies of Mt. Pinatubo aerosol layers over Laramie, Wyoming during summer 1991
Author(s) -
Sheridan Patrick J.,
Schnell Russell C.,
Hofmann David J.,
Deshler Terry
Publication year - 1992
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/91gl02789
Subject(s) - aerosol , sulfate , particle (ecology) , ammonium sulfate , particle counter , volcano , mineralogy , single particle analysis , sulfate aerosol , nucleation , atmospheric sciences , particle size , analytical chemistry (journal) , materials science , chemistry , geology , meteorology , environmental chemistry , physics , oceanography , geochemistry , metallurgy , organic chemistry
Stratospheric aerosol layers resulting from the June 1991 eruptions of Mt. Pinatubo were first observed over Laramie, Wyoming in July 1991. Atmospheric particles were collected from these layers during three balloon flights in July and August using cascade impactors. Analytical electron microscope analysis of the aerosol deposits indicated that a large majority (> 99%) of the fine particles in all three samples were collected as submicrometer aqueous H 2 SO 4 droplets, which changed to (NH 4 ) 2 SO 4 particles over time. Other particles observed in the aerosol were larger, and consisted of supermicrometer sulfate particles and composite sulfate/crustal particles which ranged up to ∼10 μm in size. Peak aerosol concentrations for r > 0.15 μm diameter particles (determined by optical particle counters) in the layers were higher for the July flights than for the August sounding. This was reflected in the electron microscope results, which showed that the July impactor samples had particulate loadings on the fine particle stages which were 20–30% higher than those from the corresponding substrate from the August sample. A detailed analysis of the fine sulfate aerosol was performed to assess whether the sulfate particles contained small condensation nuclei. Nearly all analyzed sulfate particles showed no evidence of a solid or dissolved nucleus particle, which suggests that the volcanic H 2 SO 4 aerosol formed through homogeneous nucleation processes. These data support heated‐inlet optical particle counter data from the balloon flights which suggest that 95–98% of the volcanic particles were aqueous H 2 SO 4 .