Sources and variability of ice-nucleating particles in the Southern Ocean region measured with PINEair on board the HALO aircraft

Ice Nucleating Particles (INPs) are a minor, strongly temperature-dependent subset of atmospheric aerosol particles that initiate primary ice formation (e.g., Forster et al., 2021). In cirrus and mixed-phase clouds (MPCs), they have an influence on the Earth’s radiative budget, and in MPCs, ice crystals often initiate the formation of precipitation. Over the past decades, various measurements were performed at boundary layer field sites to measure the INP concentration at mixed-phase cloud conditions (e.g., data compiled in Kanji et al., 2017). However, there is a lack of INP measurements in the free troposphere, as they can only be conducted by aircraft-based measurements or at high altitude mountain stations. In order to better understand and predict the formation of MPC and cirrus clouds, as well as their role in the climate system, direct INP measurements at different altitudes are required.

The HALO-South campaign, which investigated the interplay of clouds, aerosols and radiation above the Southern Ocean, took place in New Zealand in September/October 2025. For the first time, our newly developed INP instrument, PINEair (Portable Ice Nucleation Experiment airborne; Bogert, 2024), was on board the HALO aircraft. The instrument is a further development of the expansion-type cloud chamber design of PINE (Möhler et al., 2021). PINEair can measure INPs in an automated way at both mixed-phase cloud and cirrus cloud temperatures down to -60 °C with a time resolution of about 2min.

In this contribution, we present first results of the INP concentration measured at different temperatures during various flights, ranging from very clean air masses originating from Antarctica to more polluted ones from Australia. The PINEair measurements were successfully performed over a wide altitude range, covering the boundary layer up to the free troposphere.

 

References

Bogert, P. Ice-nucleating particles in the free troposphere: long-term observation and first measurements at cirrus formation temperatures using the novel Portable Ice Nucleation Experiment PINEair, Ph.D. thesis, Karlsruhe Institute of Technology, https://doi.org/10.5445/IR/1000174265, 2024.

Kanji, Z., et al. Ice formation and evaluation in clouds and precipitation: Measurement and modeling challenges, Meteorological Monographs, 58, 2017.

Möhler, O., et al. The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles, Atmospheric Measurement Techniques, 14, 1143–1166, 2021.

Forster, P., T. Storelvmo, K. Armour, et al. The Earth’s Energy Budget, Climate Feedbacks, and Climate Sensitivity, In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 923–1054, doi:10.1017/9781009157896.009, 2021.