Ice nucleation in sulfuric acid/organic aerosols: Implications for cirrus cloud formation

Abstract

Using an aerosol flow tube apparatus, we have studied the effects of aliphatic aldehydes (C3 to C10) and ketones (C3 and C9) on ice nucleation in sulfuric acid aerosols. Mixed aerosols were prepared by combining an organic vapor flow with a flow of sulfuric acid aerosols over a small mixing time (~60 s) at room temperature. No acid-catalyzed reactions were observed under these conditions, and physical uptake was responsible for the organic content of the sulfuric acid aerosols. In these experiments, aerosol organic content, determined by a Mie scattering analysis, was found to vary with the partial pressure of organic, the flow tube temperature, and the identity of the organic compound. The physical properties of the organic compounds (primarily the solubility and melting point) were found to play a dominant role in determining the inferred mode of nucleation (homogenous or heterogeneous) and the specific freezing temperatures observed. Overall, very soluble, low-melting organics, such as acetone and propanal, caused a decrease in aerosol ice nucleation temperatures when compared with aqueous sulfuric acid aerosol. In contrast, sulfuric acid particles exposed to organic compounds of eight carbons and greater, of much lower solubility and higher melting temperatures, nucleate ice at temperatures above aqueous sulfuric acid aerosols. Organic compounds of intermediate carbon chain length, C4-C7, (of intermediate solubility and melting temperatures) nucleated ice at the same temperature as aqueous sulfuric acid aerosols. Interpretations and implications of these results for cirrus cloud formation are discussed.

Publisher

European Geosciences Union / Copernicus Publications

Publication Date

8-4-2006

Publication Title

Atmospheric Chemistry and Physics

Department

Chemistry and Biochemistry

Document Type

Article

DOI

https://dx.doi.org/10.5194/acp-6-3231-2006

Keywords

Ammonium sulfate particles, Acid solutions, Heterogeneous chemistry, Upper troposphere, Acetone, H2SO4, Temperatures, Organics, FTIR

Language

English

Format

text

Link to Full Text

Share

COinS