In the following I set out how my team have addressed the individual ‘activities’ set out in my original proposal.
Activity 1. Construct a new-concept semi-autonomous ultra-sensitive INP counter
We have developed an instrument using microfluidically generated droplets in studies of heterogeneous freezing. We demonstrated that the technique works for a range of atmospherically relevant ice nucleating particle types and also some samples of aerosol sampled from the air. The advantage of this technique is the huge number of droplets that can be analysed, while also working all the way down to homogeneous freezing at around -37 C.
Activity 2: Developing new capacity to make INP measurements in the remote marine atmosphere
INP concentrations in many environments are poorly constrained, in part, because the community has not had adequate means to access those environments. We have constructed the IcePod, a mobile laboratory based around a converted shipping container. The IcePod is an insulated, air conditioned, facility which allows my team to perform aerosol sampling and ice nucleation experiments in environments were ice nucleation has never been measured. The laboratory is equipped with an inlet system, aerosol instrumentation, filter sampling systems, capacity for an aerosol based INP system (the PINE chamber), the NIPI suite of instruments including the microfluidics instrument.
We have developed a new expansion chamber for counting INP, known as PINE (Portable expansion chamber for Ice Nucleating particle mEasurements), in collaboration with Karlsruhe Institute of Technology (KIT). PINE has been put through an intensive testing period and has been deployed in multiple places around the world and there is now a commercial version available.
We have used Scanning Electron Microscopy (SEM) to study the size resolved composition of aerosol samples which we do in parallel to the filter based INP studies to inform us of the composition of aerosol and help relate INP concentrations to aerosol size and composition.
Activity 3: Quantify and characterise INP in marine environments
My team have done field campaigns around the world, from Barbados to the North Pole and the Finnish forests to the Iceland. These results have shown that sea spray INP are very important in marine locations remote from land, whereas the terrestrial environment provides a much stronger source of more active INPs. These campaigns have given us the underpinning data and understanding to model the global distribution of INPS from the oceans and deserts of the world.
Activity 4: Modelling the global distribution of marine INP
As part of this activity we now have a global distribution of INP associated with marine sources (Vergara-Temprado et al. 2017). In this work we parameterised INP measurements and linked this to the production of sea spray in a global aerosol model (GLOMAP). We also represented desert dust in order that we could study the competition between desert dust and marine sources of INP. We conclude that marine INP dominate in the world’s remote oceans, such as the Southern Ocean.
We then went on to incorporate the model INP concentrations in a global weather model. We demonstrated that with our representation of marine INP (i.e. low concentrations) we could reproduce the cloud fields in this region, which helps to solve the Southern Ocean bias (Vergara-Temprado et al. 2018). This places INP of first order importance for uncertainty in cloud-climate feedbacks and climate projections (Murray et al. 2021). In addition, we have shown that INP in the tropics are of first order importance in defining the development and properties of deep convective clouds in the tropical Atlantic (Hawker et al., 2021).
