HR: 15:25h
AN: A33C-08    [Abstracts]
TI: Physical State of Aqueous Sulfate-Nitrate-Ammonium-Proton Aerosol Particles
AU: * Martin, S T
EM: smartin@deas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, Cambridge, MA 02138 United States
AU: Schlenker, J C
EM: schlenk@fas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, Cambridge, MA 02138 United States
AU: Malinowski, A
EM: adma@deas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, Cambridge, MA 02138 United States
AU: Hung, H
EM: hmhung@deas.harvard.edu
AF: Harvard University, Division of Engineering and Applied Sciences, Cambridge, MA 02138 United States
AU: Rudich, Y
EM: Yinon.Rudich@weizmann.ac.il
AF: Weizmann Institute, Department of Environmental Sciences, Rehovot, 76100 Israel
AB: The crystals formed at 293 K by aerosol particles composed of SO42-, NO3-, NH4+, and H+ are determined by aerosol flow tube infrared spectroscopy. An innovative experimental protocol is employed to restore water content to the aerosol particles and thus remove the ambiguity of their physical state after exposure to low relative humidity. The six crystals formed include (NH4)2SO4, (NH4)3H(SO4)2, NH4HSO4, NH4NO3, 2NH4NO3(NH4)2SO4, and 3NH4NO3(NH4)2SO4. The dependence of which crystals form on aqueous chemical composition is reported. The infrared signatures of these crystals are determined. The infrared spectra of 2NH4NO3(NH4)2SO4 and 3NH4NO3(NH4)2SO4 and their formation in aerosol particles are reported for the first time. The formation of NH4HSO4 and NH4NO3 in initially homogeneous aerosol particles is also reported for the first time: the crystallization occurs only after another crystal has already formed, indicative that heterogeneous nucleation is necessary for their formation. For some chemical compositions, in a fraction of the aerosol particles, metastable crystals that form at low relative humidity reconstruct to thermodynamically stable crystals at higher relative humidity. An externally mixed aerosol results. Contact ion pairs are apparent in the infrared spectra of aerosol particles that do not crystallize even to 1% relative humidity. Taken together, our findings suggest a more diverse array and more frequent occurrence of crystalline SO42-/NO3-/NH4+/H+ aerosol particles in the troposphere than currently considered in the literature.
UR: http://www.deas.harvard.edu/environmental-chemistry/pubs.php
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0345 Pollution--urban and regional (0305)
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting