Our laboratories provide world-class facilities for carrying out innovative experiments on atmospheric aerosols, clouds and ice formation. Our laboratories are also used to build and prepare instruments for field campaigns taking place across the world in meteorology, aerosol and cloud physics and chemistry, using facilities such as research aircraft and ships.
Ice nucleation in the laboratory
Ice nucleation in clouds has a profound impact on cloud properties and hence climate. From soot to bacteria, we investigate atmospherically relevant particles suspended in droplets, as well as measuring ice nucleation in natural samples such as desert dust and seawater, using our Nucleation by Immersed Particle Instruments (NIPI) suite. Recent advances include the discovery that one particular mineral group, the feldspars, is what makes desert dust good at nucleating ice, rather than clays, as previously thought (Atkinson et al. Nature, 2013).
Ice nucleation in the field
Our lab science forms the basis of field studies as we apply new methods of measuring the concentration of atmospheric ice-nucleating particles around the world. For example, we have recently gathered and analysed seawater samples from research ships in the Arctic and Atlantic Oceans. The FAAM research aircraft has enabled us to collect atmospheric data from the Arctic Circle and Sahara; Cape Verde will be the base for the upcoming ICE-D campaign.
We are all familiar with the hexagonal shape of snowflakes and ice crystals, and it is well established that their six-fold symmetry is derived from the arrangement of water molecules in a hexagonal crystal structure. However, recent experiments using our X-ray diffractometer have shown that ice in a wide range of cloud types, from cirrus to contrails as well as diamond dust, may not always conform to this standard structure. Instead, sequences of the hexagonal structure can be interlaced with cubic sequences to create a 'stacking disordered ice' (Malkin et al. PNAS, 2012 and Malkin et al. PCCP, 2014).
Aerosol phases and kinetic limitation
Recreating conditions found in the atmosphere, we measure at what point droplets pass from one phase to another using a Raman microscope. For instance, atmospheric organic aerosols can be so viscous that they behave like solids, meaning that they are capable of nucleating ice in cold cirrus clouds (Murray, Nature Geoscience, 2010). We also measure the rate at which water molecules diffuse in ultraviscous liquids and glassy solids using our Raman microscope with a new isotope tracer method (Price, ACP, 2014). This enables us to predict how aerosol particles will respond to changes in atmospheric conditions, which improves our understanding of how they form clouds, scatter radiation and affect the chemistry of the atmosphere.
Ice nucleation in industry
Our fundamental atmospheric ice-nucleation work has provided critical insights into what nucleates ice in nature. This knowledge can be developed to bring social and economic benefits through potential commercial applications such as in-vitro fertilisation and regenerative medicine, which we are currently investigating with partners Asymptote Ltd.