In the atmosphere, minerals suspended in cloud droplets promote the formation of ice. We investigated ice formation in the presence of pure and binary mixtures of common minerals using a microfluidic device. The mineral with the best ability to initiate ice formation alone (that is, at the highest temperature) typically determined when ice formed in the binary mixture.

We analyzed the ability of silver iodide particles (a commonly used cloud-seeding agent) to form ice crystals in naturally occurring liquid clouds at −5 to −8 °C and found that only ≈ 0.1 %−1 % of particles nucleate ice, with a negative dependence on temperature. By contextualizing our results with previous laboratory studies, we help to bridge the gap between laboratory and field experiments, which also helps to inform future cloud-seeding projects.

Aerosol emissions from aircraft engines contribute to the formation of contrails, which have a climate impact comparable to that of aviation’s CO₂ emissions. We show that emissions of volatile particulate matter – from fuel sulphur, unburned fuel, and lubrication oil – can increase the number of ice particles formed within a contrail, and therefore have an important role in the climate impacts of aviation. This has implications for emissions regulation and climate mitigation strategies.

Two nucleation schemes are used to study ice nucleation, focusing on three ice sources: mountains, turbulence and anvils. Ice from mountains is concentrated in mid- and high-latitudes, while ice from turbulence and anvils is more common in low and mid-latitudes. Both schemes simulate orographic cirrus clouds, with mountain ice as the dominant source. The schemes differ in how they handle ice source competition, causing turbulence and anvils to influence clouds differently.

We model the cloud condensation nuclei (CCN) activation of sea spray aerosol particles with classical Köhler theory and with a new model approach that takes surface tension lowering into account. We categorize organic compounds into weak, intermediate, and strong surfactants, and we outline for which composition surface tension lowering is important. The results suggest that surface tension lowering allows sea spray aerosol particles in the Aitken mode to be a source of CCN in marine updraughts.