HR: 1340h
AN: A53A-0154    [Abstracts]
TI: Crystallization Pathways of Sulfate-Nitrate-Ammonium Aerosol Particles
AU: Schlenker, J C
EM: schlenk@fas.harvard.edu
AF: Harvard University, Div Eng Appl Sci, 29 Oxford St., Pierce Hall, Cambridge, MA 02138 United States
AU: * Martin, S T
EM: smartin@deas.harvard.edu
AF: Harvard University, Div Eng Appl Sci, 29 Oxford St., Pierce Hall, Cambridge, MA 02138 United States
AB: Atmospheric aerosol particles scatter incoming solar radiation directly back to space and serve as cloud condensation nuclei. Sulfate particles are the largest anthropogenic contribution to the global accumulation mode aerosol mass budget and significantly impact Earth's radiation budget in a cooling effect. The physicochemical behavior of the sulfate particles is strongly influenced by the presence of nitrate and ammonium. In particular, the aqueous versus crystalline phase of particles depends strongly on chemical composition. Phase, in turn, significantly impacts radiative forcing and atmospheric chemistry. For instance, given initial dry particle size distributions of 50 to 200 nm in diameter, which are typical in the troposphere, aqueous particles scatter solar radiation more efficiently than do crystalline particles. Knowledge of particle physical state is thus required to accurately determine the effect of sulfate, nitrate, ammonium, and proton particles on radiative forcing and atmospheric chemistry Crystallization experiments are conducted for aerosol particles composed of variable mixtures of (NH4)2SO4(aq) and NH4NO3(aq), (NH4)2SO4(aq) and NH4HSO4(aq), and NH4NO3(aq) and NH4HSO4(aq). Crystals of (NH4)2SO4(s), (NH4)3H(SO4)2(s), NH4HSO4(s), NH4NO3(s), 2NH4NO3.(NH4)2SO4(s), and 3NH4NO3.(NH4)2SO4(s) are formed. Characteristic infrared aerosol spectra are provided for each of these solids based upon a linear analysis of the recorded spectra. However, small nonzero residuals result because aerosol spectra depend on particle morphology, which changes slightly across the range of compositions studied. For most compositions containing NO3- and SO42-, 2NH4NO3(NH4)2SO4(s) forms more readily than 3NH4NO3.(NH4)2SO4(s). Although stoichiometric compositions of NH4NO3(aq) and NH4HSO4(aq) particles do not crystallize even to 1% relative humidity, addition of 5% SO42- or NO3- ions promotes crystallization. 2NH4NO3(NH4)2SO4(s) and (NH4)3H(SO4)2(s) appear to serve as good heterogeneous nuclei for NH4NO3(s) and NH4HSO4(s), respectively. Several of the mixed compositions crystallize with residual enclosed aqueous water pockets of up to 5% particle mass. The results provide further insights into the nonlinear crystallization pathways of sulfate-nitrate-ammonium aerosol particles.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0365 Troposphere: composition and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005