B. Zuberi

Hydrophilic properties of aged soot

[1]xa0The global presence of soot has significant effects on regional and global climate, as well as human health. Influence of soot on radiation budget, rain formation and heterogeneous chemistry, and its residence time in the atmosphere are largely dependent on its ability to interact with water. While freshly emitted soot is extremely hydrophobic, oxidation during aging causes soot to become more hydrophilic. Laboratory studies demonstrate that aged soot attracts and retains water, and can be efficiently removed from the troposphere by entrapment in existing liquid cloud droplets or by activation as cloud condensation nuclei.

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

[1]xa0Using optical microscopy, we investigated the heterogeneous nucleation of ice in aqueous (NH4)2SO4-H2O particles containing two types of mineral dusts, kaolinite and montmorillonite. The efficacy of montmorillonite and kaolinite to nucleate ice in (NH4)2SO4-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.