Clouds, ice, and bioaerosols: reducing climate uncertainty
“We are using state-of-the-art technologies to better understand the hugely important role that ice-nucleating particles play in determining the properties of clouds in the Southern Ocean, improving climate models and our ability to react to a changing climate.”
Dr Mark Tarn, Senior Research Fellow, University of Leeds
What’s the challenge we’re facing?
Climate models show that the Southern Ocean has the largest biases in surface radiation and sea surface temperature of any region in the world, significantly impacting our ability to predict global climate. Evidence suggests that these biases are due to the poor representation of mixed-phase clouds, which contain both water droplets and ice crystals.
Clouds play a critical role in our climate by reflecting solar radiation back into space as well as through precipitation – all of which are heavily influenced by the cloud’s water-to-ice ratio. This ratio is greatly influenced by aerosol particles such as ice-nucleating particles (INPs), which trigger the freezing of supercooled water droplets, forming ice crystals. However, INP observations in the Southern Ocean are scarce, making it difficult to accurately represent their concentrations, types, sources, and effects. To improve climate models, we need better INP data.
We are collaborating with the British Antarctic Survey (BAS) to better understand how aerosols influence cloud formation in the Southern Ocean. We deployed various aerosol and gas monitoring instruments to measure INPs and aerosols during a research cruise (Nov–Dec 2024) aboard the Royal Research Ship (RRS) Sir David Attenborough, led by Dr Tom Lachlan-Cope and Dr Amelié Kirchgaessner (BAS). In a further collaboration with Dr Floor van den Heuvel (BAS), we are investigating the ice-nucleating potential of Antarctic mosses and lichens – a possible natural source of bioaerosol INPs over the Southern Ocean.
What advances are we aiming for?
Real-time measurements of INPs have traditionally been difficult to achieve without compromising time or temperature resolution. However, a collaboration between the University of Leeds and Karlsruhe Institute of Technology (KIT) led to the development of the Portable Ice Nucleation Experiment (PINE) chamber – a compact, field-deployable version of KIT’s Aerosol Interaction and Dynamics in the Atmosphere (AIDA) chamber. PINE samples ambient air into a 10L chamber, then uses adiabatic expansion to form a cloud. A particle counter then detects the number of cloud droplets and ice crystals generated, allowing us to measure INP concentrations every six minutes at user-defined temperatures.
Aerosol particle size distributions in the ambient air are measured simultaneously using devices like optical particle counters (OPCs), while bioaerosol concentrations are monitored with the fluorescent particle counter, Plair Rapid-E, part of a new bioaerosol facility at Leeds. This equipment can be set up in mobile labs, such as Leeds' IcePod shipping container lab, which we deployed on the RRS Sir David Attenborough.
What have we achieved so far?
PINE represents a step-change in real-time INP measurements, and its integration with Rapid-E bioaerosol monitoring has provided a powerful tool for determining the presence and importance of bioaerosol INPs in the field.
We also performed offline INP measurements in the Southern Ocean by collecting aerosols on filters and analysing them for INPs using droplet freezing assays. Heat treatments indicated the presence of proteinaceous bioaerosol INPs in some samples, while we also measured the INP content of seawater. We are now looking at the data to find correlations between INPs, bioaerosols, and aerosol sizes across different environments.
Where next, through the Hub?
Through the Biodetection Technologies Hub, we are expanding our collaboration with BAS to investigate the ice-nucleating activity of Antarctic mosses and lichens, by testing species in the BAS Herbarium and those collected from the research cruise. Using Leeds’ aerosol chamber facilities, we will launch Antarctic dusts, soils, mosses, and lichens into controlled atmospheric conditions to assess their aerosolisation potential and ability to sustain ice-nucleating activity. These collaborations will enhance our understanding of the sources and behaviour of INPs in the Southern Ocean, contributing to more accurate climate models and better predictive capabilities.