Our knowledge of the special aerosol particles which trigger ice formation in clouds is extremely poor. This project will take some of the first ever measurements of ice nucleating particle size in order to better understand their transport.

Abstract:

It is well known that the formation of ice in a cloud can influence many of its properties from its reflectivity to its longevity it the atmosphere. Given this, the presence of ice-nucleating particles (INPs) in clouds can have a significant impact on individual clouds and on climate as a whole. However, currently, little is known about the origins, the abundance and the transportation of these particles in the atmosphere. Doubtless, understanding the size and distribution of INP in the atmosphere would help to deepen our understanding of their lifetimes, but few studies have examined this aspect of cloud formation. Furthermore, improving understanding of INPs in the atmosphere will help to inform climate models due to the uncertainty in the cloud radiative effect and how this may change with future warming.

Given this, the proposed project will aim to investigate the size, sources and transport of INPs in the atmosphere by utilising the newly developed SHARK (Selective Height Aerosol Research Kit). The SHARK will be used to collect size resolved aerosol for offline INP analysis by using cascade impactors to separate the aerosol sample into different size bins. This radio-controlled payload has been designed to be attached to a tethered balloon, allowing the collection of aerosol particles from much higher altitudes without the use of aircraft. The aim of this is to investigate size distribution of INP at different locations and at different altitudes, to examine the different sources of INPs and investigate whether they are transported to atmospherically relevant altitudes for cloud formation. The collected aerosol samples will be analysed using off-line droplet freezing techniques to determine the size resolved INP concentrations and active ice fractions. Then, further analysis will be required to get a better understanding of the source and composition of the INP. Scanning electron microscopy (SEM) will be used to examine the morphology of the aerosols collected and energy dispersive X-ray spectroscopy (EXD) will be used to examine their chemical composition.