Oxalic acid as a heterogeneous ice nucleus in the upper troposphere and its indirect aerosol effect

Zobrist, B.; Marcolli, C.; Koop, T.; Luo, B. P.; Murphy, D. M.; Lohmann, U.; Zardini, A. A.; Krieger, U. K.; Corti, T.; Cziczo, D. J.; Fueglistaler, S.; Hudson, P. K.; Thomson, D. S.; Peter, T.

Heterogeneous ice freezing points of aqueous solutions containing various immersed solid dicarboxylic acids (oxalic, adipic, succinic, phthalic and fumaric) have been measured with a differential scanning calorimeter. The results show that only the dihydrate of oxalic acid (OAD) acts as a heterogeneous ice nucleus, with an increase in freezing temperature between 2 and 5 K depending on solution composition. In several field campaigns, oxalic acid enriched particles have been detected in the upper troposphere with single particle aerosol mass spectrometry. Simulations with a microphysical box model indicate that the presence of OAD may reduce the ice particle number density in cirrus clouds by up to ~50% when compared to exclusively homogeneous cirrus formation without OAD. Using the ECHAM4 climate model we estimate the global net radiative effect caused by this heterogeneous freezing to result in a cooling as high as −0.3 Wm −2.

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Zobrist, B. / Marcolli, C. / Koop, T. / et al: Oxalic acid as a heterogeneous ice nucleus in the upper troposphere and its indirect aerosol effect. 2006. Copernicus Publications.

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