Purely Inorganic Highly Efficient Ice Nucleating Particle

Mainak Ganguly; Simon Dib; Parisa A Ariya

doi:10.1021/acsomega.7b01830

Purely Inorganic Highly Efficient Ice Nucleating Particle

ACS Omega. 2018 Mar 20;3(3):3384-3395. doi: 10.1021/acsomega.7b01830. eCollection 2018 Mar 31.

Authors

Mainak Ganguly¹, Simon Dib², Parisa A Ariya^{1

2}

Affiliations

¹ Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec H3A 0B9, Canada.
² Department of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada.

Abstract

To evaluate the role of atmospheric heterogeneous reactions on the ice nucleation ability of airborne dust particles, we investigated the systematic study of ice nucleation microphysics with a suite of atmospherically relevant metals (10), halides (4), and oxyhalides (2). Within a minute, a kaolin-iron oxide composite (KaFe) showed efficient reactions with aqueous mercury salts. Among the different mercury salts tested, only HgCl₂ reacting with KaFe generated HgKaFe, a highly efficient ice nucleating particle (HEIN). When added to water, HgKaFe caused water to freeze at much warmer temperatures, within a narrow range of -6.6 to -4.7 °C. Using a suite of optical spectroscopy, mass spectrometry, and microscopy techniques, we performed various experiments to decipher the physical and chemical properties of surface and bulk. KaFe was identified as a mixture of different iron oxides, namely, goethite, hematite, magnetite, and ε-Fe₂O₃, with kaolin. In HgKaFe, HgCl₂ was reduced to Hg₂Cl₂ and iron was predominantly in maghemite form. Reduction of Fe²⁺ by NaBH₄, followed by aerial oxidation, helped KaFe to be an exact precursor for the synthesis of HEIN HgKaFe. Kaolin served as a template for synthesizing iron oxide, opposing unwanted aggregation. No other metal or metal halide was found to have more efficient nucleating particles than HgCl₂ with KaFe composite. The chelation of Hg(II) hindered the formation of HEIN. This study is useful for investigating the role of morphology and how inorganic chemical reactions on the surface of dust change morphology and thus ice nucleation activity. The understanding of the fundamentals of what makes a particle to be a good ice nucleating particle is valuable to further understand and predict the amount and types of atmospheric ice nucleating particles.