Using microfluidic technology to measure and identify atmospheric ice nucleating particles
Prof. Ben Murray (School of Earth and Environment, University of Leeds) Dr Jung-uk Shim (School of Physics and Astronomy, University of Leeds) Dr Daniel McCluskey (University of Hertfordshire) Dr Mark Tarn (School of Earth and Environment, University of Leeds)
Contact Ben Murray to informally discuss the project in advance of the application deadline (3rd Feb): [email protected]
Summary
Our lack of knowledge of how clouds will respond to a changing climate represent one of the largest sources of uncertainty in our projections of future climate (Tan et al., 2016). A major source of this uncertainty is related to special aerosol particles, known as ice-nucleating particles (INPs) which are needed to trigger ice formation in clouds. Once ice crystals form a cascade of processes triggers precipitation and leads to dramatic changes in cloud coverage and cloud reflectivity. However, the sources, characteristics and distribution around the globe of atmospheric ice nucleating particles is extremely poorly understood. In part, this is due to our lack of instrumentation capable of making the necessary measurements of INP and our ability to identify the aerosol particle types which nucleate ice.
To tackle this problem we have developed a microfluidic system which generates 100s of droplets a second in a channel and flows them over a cold plate and counts the fraction that freeze. In a further development we can now separate frozen from unfrozen droplets for off chip analysis which in principle allows us to analyse the composition and properties of ice nucleating particles. This system offers Ice nucleating particles (INPs) high throughput with extremely low levels of contamination strongly impact clouds. For example, with the possibility of automation. This will take us to a in these massive oceanic cloud new level of automation, statistics and coverage of the systems the introduction of INPs parameter space. strongly reduces the amount of supercooled water and the reflectivity of cold clouds. The correct Objectives representation of clouds like these is critical for climate predictions and depends on measurements of ice The overarching goal of this project is to make use of and nucleating particles (Vergara- further develop our recently constructed microfluidics Temprado et al., 2018). platform for quantifying atmospheric ice nucleating particle concentrations. This will involve:
1. Learning to use our existing systems for quantifying ice nucleation in atmospheric samples.
2. Use our aerosol sampling equipment at the new Leeds Atmospheric Observatory to collect samples for analysis with the microfluidics system
3. Develop analytical tools to characterise the particles in frozen droplets, relative to unfrozen droplets, which will be separated with our new sorting device. 4. Develop a technique to sample aerosol into liquid water which is then fed directly into the microfluidic device. This would be a powerful micro total analysis system.
Background science
Atmospheric ice-nucleating particles (INP) are aerosol particles with special physical and chemical properties that enable them to induce the formation of ice crystals in clouds below 0°C. In the absence of INP, cloud droplets can supercool to below -33°C. Formation of ice in clouds is a fundamental process that initiates most of the global precipitation. It also has profound effects on the radiative properties of clouds and thereby influences the effect that We think that biological fragments clouds have on climate. For example, we recently which nucleate ice are extremely demonstrated that the low INP concentrations above the important INP, but do not know what Southern Ocean leads to clouds which persist in a their dominant sources are or their supercooled state, but are extremely sensitive to changes atmospheric concentration. in INP concentration (Vergara-Temprado, 2018). (O’Sullivan et al. 2015).
There are different types of clouds in which ice is important, but the type and mode of action through which INP nucleate ice is distinct in the different cloud regimes. In the lower and mid troposphere at temperatures between 0 and -35oC clouds can exist as supercooled water, ice or a mixture of the two. In this regime, INP tend to be immersed in supercooled water before they can trigger freezing. In contrast, in the upper troposphere under cirrus conditions ice can form directly onto aerosol particles well below the supersaturation required to form a liquid cloud. In fact, different populations of aerosol serve as INPs in the different cloud regimes, hence measurements need to be made that distinguish between these different populations.
Despite decades of research on INP, our understanding of INP sources in the atmosphere, and hence their impact on climate, is in its infancy. Substantial developments are being made by characterizing INP in innovative laboratory and field experiments, and then carrying this new knowledge into atmospheric models. For example, the Leeds group discovered that a specific mineral group in desert dust particles can explain their ice nucleating properties, enabling a global model of these INP to be developed (Atkinson et al., 2013). Similarly, we quantified marine organic INP through field measurements in remote environments from research ships and then used our global model to represent the global distribution of these INP (Wilson et al. 2015; Vergara-Temprado et al. 2017).
Our new microfluidic INP instrument (LOC-NIPI)
Microfluidics is a technology which allows the generation of micron scaled droplets within a channel on a chip with droplet production rates of Schematic showing the principle of droplet freezing up to many thousands per second. We have in continuous flow for ice-nucleating particle (INP) developed a microfluidic platform for the study of analysis. Aqueous droplets containing sampled atmospheric ice-nucleating particles (INPs) via on- aerosols pass over a cold plate set to a temperature chip freezing analysis of droplets in continuous below 0 °C, and the fraction of droplets that freeze flow. This complements our other instruments where we can study ~50 droplets an hour. In LOC- is NIPI droplets are generated using a flow focussing determined. The process is then repeated for nozzle, then passed across a cold stage and a high speed camera is used to monitor the phase of the droplets. By flowing droplets over the cold plate we can then count the fraction of droplets which are frozen at this temperature and then repeat the process at a different temperature. We have tested this instrument against a range of standard ice nucleating materials and used it in its first field campaign in Israel in 2018. The next steps in this project are using LOC-NIPI in new field environments (e.g. we were recently funded to go the Labrador Sea on a ship cruise and there is an opportunity for the successful student to join this cruise). As part of this project we will also work on combining LOC-NIPI with an aerosol-into-liquid sampler in order to create an instrument which both samples aerosol and analyses its ice nucleating ability.
We have also recently developed a second stage where we can sort frozen and unfrozen droplets into two separate channels based on buoyancy. This potentially allows us simply the data analysis (we would not need an expensive and data intensive high speed camera) as well as allowing the analysis of the composition of aerosol in the frozen vs unfrozen The construction of the LOC- droplets. This NIPI microfluidics system. will allow us to say which aerosol are nucleating ice.
Research environment in Leeds
You will join the vibrant Ice Nucleation group in the Institute for Climate and Atmospheric Science Droplets freezing in flow. (ICAS). ICAS covers climate, air pollution, meteorology and climate impacts, with extensive programmes in observations, modelling and lab studies. Atmospheric science at Leeds is ranked 9th in the Centre for World University Rankings (http://cwur.org/2017) and 13th in the Academic Ranking of World Universities out of 400 (http://www.shanghairanking.com). Wider interdisciplinary experience is guaranteed through our new cross-campus Priestley Centre (http://climate.leeds.ac.uk). Peer exchange and learning occurs through frequent institute and group seminars, discussion meetings and paper review groups.
We also have formal partnerships with both the UK Met Office and also the Karlsruhe Institute of Technology. The KIT-ICAS partnership has led to exchange of students and staff and many joint publications.
The supervisors have an outstanding track record of PhD student supervision, with students having won School of Earth and Environment PhD publication prize (out of 200 students), the Piers Sellers Priestly prize as well as several national and international prizes.
The new Atmospheric Observatory
The University of Leeds has recently made a £3 million investment in the University of Leeds Research Farm and as part of this we are constructing a new Atmospheric Observatory. This facility will allow us to perform ambitious INP measurements on our doorstep. The Atmospheric Observatory will consist of space and power for several mobile laboratories, aerosol samplers, a drone landing pad, a 12 m high walk-up tower, an advanced Raman Lidar and plans for much more in the future.
The plan for the new Atmospheric Observatory, which is currently under construction.
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