| Autor: |
Renbaum-Wolff, L., Song, M., Marcolli, C., Zhang, Y., Liu, P. F., Grayson, J. W., Geiger, F. M., Martin, S. T., Bertram, A. K. |
| Zdroj: |
Atmospheric Chemistry & Physics Discussions; 2015, Vol. 15 Issue 22, p33379-33405, 27p |
| Abstrakt: |
Particles consisting of secondary organic material (SOM) are abundant in the atmosphere. To predict the role of these particles in climate, visibility, and atmospheric chemistry, information on particle phase state (i.e. single liquid, two liquids, solid and so forth) is needed. This paper focuses on the phase state of SOM particles free of inorganic salts produced by the ozonolysis of a-pinene. Phase transitions were investigated both in the laboratory and with a thermodynamic model over the range of < 0.5% to 100 % relative humidity (RH) at 290 K. In the laboratory studies, a single phase was observed from 0 to 95 % RH while two liquid phases were observed above 95 % RH. For increasing RH, the mechanism of liquid-liquid phase separation (LLPS) was spinodal decomposition. The RH range at which two liquid phases were observed did not depend on the direction of RH change. In the modelling studies at low RH values, the SOM took up hardly any water and was a single organic-rich phase. At high RH values, the SOM underwent LLPS to form an organic-rich phase and an aqueous phase, consistent with the laboratory studies. The presence of LLPS at high RH-values has consequences for the cloud condensation nuclei (CCN) activity of SOM particles. In the simulated Köhler curves for SOM particles, two local maxima are observed. Depending on the composition of the SOM, the first or second maximum can determine the critical supersaturation for activation. The presence of LLPS at high RH-values can explain inconsistencies between measured CCN properties of SOM particles and hygroscopic growth measured below water saturation. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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