School of Earth and Environment

Climate and Atmospheric Science (ICAS) PhD Projects

Designer ice nuclei for geoengineering of clouds

Supervisors: Dr Ben Murray, Dr Steven Dobbie, and Dr John Morris (Asymptote Ltd, St John's Innovation Centre, Cambridge. UK)

Deadline for applications: 12:00 Tuesday 2nd May. 

Fully-funded 3.5 year NERC CASE studentship (CASE partner is Asymptote Ltd.).  Eligibility criteria is at http://www.nerc.ac.uk/funding/available/postgrad/eligibility.asp). 

Overview

The collective international failure to curb rises in greenhouse gas emissions means we need to consider back up plans to avoid the worst potential impacts of climate change.  A number of geoengineering schemes have been put forward and one of these involves modifying cirrus ice clouds.  Thin cirrus clouds have a net warming effect on the planet, but by seeding them with efficient ice nuclei their global coverage could be reduced thus resulting in a cooling of the planet (Mitchell and Finnegan, 2009). Research is urgently needed into the basic science that will underpin schemes such as this.

We propose a laboratory experimental study to identify materials which could be used to efficiently, safely and cost effectively nucleate ice (ice nuclei) in any future cloud geoengineering projects.  In order to use ice nucleation to control cloud properties we need seed materials which serve as efficient ice nuclei in the target cloud, but do not detrimentally impact other clouds at a later time, are not toxic and are cheap to mass produce.  The pool of existing ice nuclei is restricted and most do not meet these criteria.  We will focus our efforts on porous materials which have received very little attention in the past.  Our strategy is to build on the experience and expertise at Asymptote Ltd who are experts in ice nucleation in the field of cryopreservation of biological samples.  Ben Murray already has an established working relationship with Asymptote and has published with them on freezing of water in jet fuel (Murray et al., 2011).  Our goal is to develop a fundamental understanding of ice nucleation by porous materials and use this to design ice nuclei which would be ideal for a range of applications.  The primary focus of the student will be to identify ice nuclei for geoengineering purposes with potential benefits for society, whereas Asymptote Ltd will apply the same fundamental information to the commercial area of cryopreservation.  

Project objectives

  • Design and test ice nuclei with geoengineering potential through a fundamental approach in collaboration with Asymptote Ltd who are experts in commercial applications of ice nucleation.
  • Develop a fundamental understanding of ice nucleation by porous materials which could be used to create particles with the desired ice nucleating properties.
  • Quantify the nucleating efficiency in the deposition and immersion mode of particles identified as potential geoengineering ice nuclei.
  •  Apply this new knowledge to other areas of science and technology which also require non-toxic ice nuclei, such as cryopreservation through Asymptote.

Scientific rationale

Water droplets free of solid particles can supercool to about -37oC before freezing homogeneously, but freezing can be catalysed at much higher temperatures in the presence of a particle of the correct material (ice nuclei).  Similarly, air can become supersaturated with respect to ice in the absence of ice nuclei.  Not all solid materials serve as effective ice nuclei and those that do, nucleate ice with different efficiencies under different conditions (Dymarska et al., 2006;Murray et al., 2010b).  Unfortunately our ability to predict which particles will serve as ice nuclei remains poor.  For example, in older texts ice nucleation by the mineral kaolinite is explained by a good match between the crystal structure of ice and one of the exposed crystal faces of kaolinite (Pruppacher and Klett, 1997).  However, recent computational studies reveal that this model is incorrect and ice nucleation may be related to defects, cracks or even pores in kaolinite (Hu and Michaelides, 2009) and our recent work suggests kaolinite is not as efficient as previously thought (Murray et al., 2010b).

However, progress is being made in other areas of nucleation science.  In the field of structural biology there is a desire to crystallise proteins in order to determine their crystal structure which is pivotal in the success of drug design, but these proteins are notoriously difficult to crystallise.  In recent years workers in this field have focused on nucleation by nano-porous materials.  This was in part motivated by a theoretical study by Page and Sear (2006) who proposed a two step model for nucleation in pores which suggest that there is an ideal pore size for nucleating a particular compound under specific conditions.  This has led to some success in identifying nuclei for proteins (Saridakis and Chayen, 2009) and provides a theoretical framework in which to identify porous materials for geoengineering purposes.

Asymptote Ltd have discovered a range of mesoporous materials, when suspended in millimetre sized water droplets, can nucleate ice as high as -5oC, which is a remarkably high temperature.  In micron sized droplets, kaolinite nucleated ice below -33oC (Murray et al., 2010b).  This work now needs to be extended to atmospherically relevant conditions.

Programme of research

The student will spend a total of 6 months at Asymptote Ltd working with Dr John Morris where they will screen a range of porous material for ice nucleating potential.  Asymptote Ltd was recently awarded funds from the Technology Strategy Board to investigate ice nucleation by porous materials for use in cryopreservation equipment.  Materials will include molecular sieves, activated carbon, zeolites and porous gel–glasses.

 

The student will then quantify the ice nucleating efficacy of this material under atmospherically relevant conditions.  In Leeds we have equipment for quantifying the rate at which ice nucleates on particles suspended in supercooled water (Murray et al., 2010a;Murray et al., 2010b) or exposed to air supersaturated with respect to ice (Kulkarni and Dobbie, 2010).  These instruments have been specifically designed to separate the time and temperature dependence of nucleation, unlike cloud chamber instruments or continuous flow diffusion chambers where the range of exposure times to high supersaturations is limited.

The time spent at Asymptote will provide an opportunity to experience a commercial research environment and will learn skills that the School of Earth and Environment does not offer such as management of intellectual property and the importance of commercial confidentiality.  This combined with training in the fundamentals of nucleation and crystallisation as well as the transferrable skills training all Leeds students receive will give this individual a very competitive portfolio.

Requirements

The successful student will ideally have (or have the potential to achieve):

  • An undergraduate degree in an appropriate physical science (e.g. environmental science, physics, chemistry, engineering etc)
  • Practical laboratory experience
  • Experience in a research environment
  • Drive and ambition
  • Ability/potential to work independently
  • Work as part of a wider research team
  • Contribute to cloud-aerosol community in Leeds and beyond
  • Under guidance write high quality papers for the peer reviewed literature
  • Develop communication skills and present at international conferences
  • Able to spend 6 months out of 3.5 years in Cambridge

Finances

The award pays tuition fees, a stipend at the UK research council rate (£13,590 for 2011/12), plus a CASE top-up of £2.5K per year (contributed by Asymptote Ltd).

Further information

References

  • Dymarska, M., Murray, B. J., Sun, L. M., Eastwood, M. L., Knopf, D. A., and Bertram, A. K.: Deposition ice nucleation on soot at temperatures relevant for the lower troposphere, J. Geophys. Res., 111, 2006.
  • Hu, X. L., and Michaelides, A.: Ice formation on kaolinite: Lattice match or amphoterism?, Surface Science, 601, 5378–5381, 2009.
  • Kulkarni, G. R., and Dobbie, S.: Ice nucleation properties of mineral dust particles: Determination of onset rhi, in active fraction, nucleation time-lag, and the effect of active sites on contact angles, In preparation for J.Atm. Chem. Phys., 10, 95-105, 2010.
  • Mason, B. J.: The physics of clouds, Clarendon Press, Oxford, 1971.
  • Mitchell, D. L., and Finnegan, W.: Modification of cirrus clouds to reduce global warming, Environ. Res. Lett., 4, doi:10.1088/1748-9326/1084/1084/045102, 2009.
  • Murray, B. J., Broadley, S., Wilson, T. W., Bull, S., and Wills, R.: Kinetics of the homogeneous freezing of water, Phys. Chem. Chem. Phys., 12, 10380-10387, DOI: 10310.11039/c003297b, 2010a.
  • Murray, B. J., Wilson, T. W., Broadley, S. L., and Wills, R. H.: Heterogeneous freezing of water droplets containing kaolinite and montmorillonite particles, Atmos. Chem. Phys. Discuss., 10, 9695-9729, 2010b.
  • Murray, B. J., Broadley, S. L., and Morris, G. J.: Supercooling of water droplets in jet aviation fuel Fuel, 90, 433-435, doi:410.1016/j.fuel.2010.1008.1018 2011.
  • Pruppacher, H. R., and Klett, J. D.: Microphysics of clouds and precipitation, Kluwer, Dordrecht, 1997.
  • Saridakis, E., and Chayen, N. E.: Towards a 'universal' nucleant for protein crystallization, Trends in Biotechnology, 27, 99-106, 2009.