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

Abstract

[1] Using optical microscopy, we investigated the heterogeneous nucleation of ice in aqueous (NH 4 ) 2 SO 4 -H 2 O particles containing two types of mineral dusts, kaolinite and montmorillonite. The efficacy of montmorillonite and kaolinite to nucleate ice in (NH 4 ) 2 SO 4 -H 2 O 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 NH 4 SO 4 -H 2 O particles containing mineral dust immersions. Based on our results, we conclude mineral dust is an efficient nuclei for ice in NH 4 SO 4 -H 2 O 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.

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

“…equation 6), if the aerosol particles consist primarily of two components (e.g., submicrometer particles and supermicrometer mineral dust particles) and if the variabilities in d a,coarse and d a,fine were small. It is also important to investigate the dependence of the d a value of dust particles on their internal mixing state (whether they are coated with solution or not) because the mixing state critically affects its direct radiative effect [Ackerman and Toon, 1981] as well as its cloud microphysical properties; they would activate as cloud condensation nuclei at lower supersaturations [e.g., Takeda and Kuba, 1982] and as ice forming nuclei in the immersion-freezing mode at lower supersaturations and warmer temperatures [Zuberi et al, 2002] when they were coated with solution.…”

Does the Homogeneous Ice Nucleation Initiate in the Bulk Volume or at the Surface of Super-Cooled Water Droplets? A Review

“…Molecular dynamics simulations have contributed to shed some doubt on the validity of classical nucleation theory. Chushak and Bartell [62] and Chushak and Bartell [63] performed simulations of spontaneous phase transition in large, deeply supercooled clusters of SeF 6 . A striking result was that nucleation invariably occurred at or near the cluster's surface, despite the fact that surfaces of clusters tend to be disordered and melt at significantly lower temperatures than their cores.…”

“…Heterogeneous freezing occurs at lower supersaturation and higher temperatures than homogeneous freezing [6] [7].…”

Laboratory study of heterogeneous ice nucleation in deposition mode of montmorillonite mineral dust particles aged with ammonia, sulfur dioxide, and ozone at polluted atmospheric concentrations

“…Mineral dust aerosols are thought to play an important role as ice nuclei in mixed phase and ice clouds in the atmosphere (Zuberi et al 2002;. Evidence of Asian desert dust particles acting as effective ice nuclei at temperatures warmer than that required for homogeneous freezing was obtained from continuous flow diffusion chamber data .…”

“…In the immersion mode, all biological particles showed higher median freezing temperatures than the mineral dust particles and soot. Montmorillonite can also act as an efficient ice nucleus in immersion mode, causing aqueous (NH 4 ) 2 SO 4 -H 2 O particles to freeze at warmer temperatures (Zuberi et al 2002).…”