Using a small expansion chamber to characterise ice nucleation by high-latitude mineral dusts and volcanic ash

Ice-nucleating particles (INPs) can influence the radiative properties of clouds and therefore climate. There are many different types of INPs including mineral dusts, biological aerosols and combustion aerosols, these different types can nucleate ice at different temperatures and through different mechanisms. Therefore, an understanding of the ice-nucleating activity (INA) of each of the different types of INPs is needed to fully understand their effect on the climate system. In this thesis I use the Portable Ice Nucleation Experiment (PINE), a small cloud expansion chamber, to characterise the INA high-latitude mineral dusts and volcanic ashes.

In order to achieve this, I first characterise the temperature inside the PINE and determine that the calculated adiabatic temperature is an accurate representation of the temperature inside the PINE on the timescales and conditions used in this thesis. Measurements of the INA of high-latitude dusts from Greenland and Alaska show that they have different INAs from one another. By using the PINE to measure the INA of volcanic ash samples aged in water, aged in acid and unaged, I find that the ageing generally decreases the INA of the ashes, but to varied extents depending on the ash and the type and length of ageing. The INA results for both high-latitude dust and volcanic ash are consistent with measurements of similar samples at warmer temperatures using a cold stage measurement technique. These new PINE measurements extend the previously existing measurements to lower temperatures than was possible using the cold stage technique. The results of this thesis highlight the differences between different INP types and provide underpinning knowledge that might be used in the future to predict the effect that high-latitude dusts and volcanic ashes may have on the radiative properties of clouds.