HR: 09:15h
AN: A41B-05    [PDF]
TI: The importance of the organic aerosol component for the passivation of aqueous atmospheric particles
AU: * Kiendler-Scharr, A W
EM: a.kiendler-scharr@fz-juelich.de
AF: ICG-II: Troposph\"are, Forschungszentrum J\"ulich, J\"ulich, 52425 Germany
AU: Folkers, M
EM: m.folkers@fz-juelich.de
AF: ICG-II: Troposph\"are, Forschungszentrum J\"ulich, J\"ulich, 52425 Germany
AU: Mentel, T F
EM: t.mentel@fz-juelich.de
AF: ICG-II: Troposph\"are, Forschungszentrum J\"ulich, J\"ulich, 52425 Germany
AU: Wahner, A
EM: a.wahner@fz-juelich.de
AF: ICG-II: Troposph\"are, Forschungszentrum J\"ulich, J\"ulich, 52425 Germany
AB: Secondary tropospheric particles are often mixtures of aqueous electrolytes and soluble organic components or surfactants. The uptake kinetics of e.g.~$\rm N_2O_5$ and the thermodynamics of binary and higher mixtures of aqueous electrolytes are quite well understood. In contrast, not much is known on a quantitative basis about the modification of these properties by organic aerosol components. The hydrolysis of $\rm N_2O_5$ on aqueous aerosol surfaces of mixed inorganic and organic aerosols was used to probe the surface reactivity/water availability. The experiments were performed in the large Aerosol Chamber at the FZ-J\"ulich at room temperature and 60 - 70 % relative humidity. The ozonolysis of $\alpha$-pinene, myrcene, limonene and isoprene was utilized to condense organic components on $\rm NH_4HSO_4$ particles. The build up of the organic component was monitored by Aerosol Mass Spectrometry (Aerodyne AMS). In the terpene experiments the hydrolysis of $\rm N_2O_5$ on the particle surface was diminished by factors of 2 to 30 compared to the pure inorganic salt (reaction probability $\gamma_{N2O5}$ = 0.02). The degree of passivation depends on the organic load and the specific terpene. For purely organic particles from $\alpha$-pinene ozonolysis, which are not hygroscopic, the reaction probabilty $\gamma_{N2O5}$ is 0.00045. In the isoprene experiment the main known ozonolysis products in the particulate phase are water soluble $\alpha$-dicarbonyls. Despite the low organic mass fraction of only 6% the hydrolysis on this mixed organic/inorganic aerosol is significantly retarded by a factor of 2 ( $\gamma_{N2O5}$ = 0.01). We were able to identify mass fragments of methyl glyoxal and pyruvic acid in the particles. Moreover, there is indication by the AMS that higher molecular components are also present in the particles, possibly formed in the particulate phase. Specific addition even of high loads of the single component methyl glyoxal to $\rm (NH_4)_2SO_4$ particles did only show a smaller effect ($\gamma_{N2O5}$ = 0.014) compared to the "real" and complex ozonolysis products of isoprene. Our findings demonstrate the importance of oxidized large biogenic organics for passivation (reduced water availability at the surface) of mixed particles. But also small molecules can contribute to passivation if condensation reactions takes place which form larger (ampholytic) molecules (M. Jang et al., Science, 298, 814-817, 2002) The studies are part of the EC CASOMIO project.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0315 Biosphere/atmosphere interactions
DE: 0365 Troposphere--composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting