HR: 10:20h
AN: SA22A-01    [Abstracts]
TI: Nitric Acid Trihydrate Formation on Na-montmorillonite Clay
AU: * Mashburn, C D
EM: mashburn@colorado.edu
AF: University of Colorado Boulder, Department of Chemistry and Biochemistry/CIRES CIRES Room 318, Boulder, CO 80309 United States
AU: Gough, R V
EM: Raina.Gough@colorado.edu
AF: University of Colorado Boulder, Department of Chemistry and Biochemistry/CIRES CIRES Room 318, Boulder, CO 80309 United States
AU: Tolbert, M A
EM: tolbert@cires.colorado.edu
AF: University of Colorado Boulder, Department of Chemistry and Biochemistry/CIRES CIRES Room 318, Boulder, CO 80309 United States
AU: Toon, O B
EM: Brian.Toon@colorado.edu
AF: University of Colorado, Laboratory for Atmospheric and Space Physics Campus Box 392, Boulder, CO 80309 United States
AB: Polar stratospheric clouds (PSCs) composed of large nitric acid trihydrate (NAT) particles have recently been observed in the Arctic polar stratosphere. In addition to heterogeneous chlorine activation, large NAT particles can influence ozone (O₃) destruction by promoting denitrification due to particle sedimentation. However, potential effects on future O₃ loss are hard to determine because the formation mechanisms of these large NAT particles are still unknown. Recently, stratospheric micrometeorites have been suggested as potentially important selective nuclei for formation of PSCs. In the current study, FT-IR spectroscopy was used in a high vacuum chamber to study the heterogeneous formation of NAT on a smectite clay, Na-montmorillonite. We find that NAT forms on Na-montmorillonite at relative humidities with respect to liquid water greater than 40% and saturation ratios with respect to crystalline NAT of S_NAT > 8. This value of S_NAT is lower than all previous laboratory studies of NAT nucleation and neatly coincides with reported conditions of NAT particles observed in the field. Smectites are not only components on clay minerals, but also of micrometeorites. Thus, formation of NAT on micrometeorites is a possible mechanism for formation of large NAT particles in the Arctic polar stratosphere.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0340 Middle atmosphere: composition and chemistry
DE: 2129 Interplanetary dust
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3311 Clouds and aerosols
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005