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Heterogeneous nucleation of ice in (NH4)(2)SO4-H2O particles with mineral dust immersions

TitleHeterogeneous nucleation of ice in (NH4)(2)SO4-H2O particles with mineral dust immersions
Publication TypeJournal Article
Year of Publication2002
AuthorsZuberi, B, Bertram, AK, Cassa, CA, Molina, LT, Molina, MJ
JournalGeophysical Research Letters

Using optical microscopy, we investigated the heterogeneous nucleation of ice in aqueous (NH4)(2)SO4-H2O particles containing two types of mineral dusts, kaolinite and montmorillonite. The efficacy of montmorillonite and kaolinite to nucleate ice in (NH4)(2)SO4-H2O particles is similar. The difference in freezing temperatures, compared to the homogeneous freezing temperatures, is found to vary from 8-20 K and it is larger for particles with concentrations greater than 27 wt %. Our freezing data shows that for temperatures ranging from 239 K to 198 K, ice super-saturations between 1.35 and 1.51 are required for ice to heterogeneously nucleate in NH4SO4-H2O particles containing mineral dust immersions. Based on our results, we conclude mineral dust is an efficient nuclei for ice in NH4SO4-H2O aerosols and as a result, it can initiate the formation of upper tropospheric ice clouds at warmer temperatures and lower super-saturations in comparison to homogeneous freezing.