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

[摘要] Heterogeneous ice freezing points of aqueous solutions containing variousimmersed solid dicarboxylic acids (oxalic, adipic, succinic, phthalic andfumaric) have been measured with a differential scanning calorimeter. Theresults show that only the dihydrate of oxalic acid (OAD) acts as aheterogeneous ice nucleus, with an increase in freezing temperature between 2and 5 K depending on solution composition. In several fieldcampaigns, oxalic acid enriched particles have been detected in the uppertroposphere with single particle aerosol mass spectrometry. Simulations witha microphysical box model indicate that the presence of OAD may reduce theice particle number density in cirrus clouds by up to ~50% whencompared to exclusively homogeneous cirrus formation without OAD. Using theECHAM4 climate model we estimate the global net radiative effect caused bythis heterogeneous freezing to result in a cooling as high as−0.3 Wm⁻².

[学科分类] 大气科学