YES-27-C-01: Hygroscopic behaviour of mixed aerosol systems

Project Description:

Atmospheric aerosols play important roles in climate, air quality and human health (Shrivastava et al., 2017). Their chemical composition is diverse, including many inorganic salts, mineral dust, soot from combustion processes and organic species. Aerosols often also contain a significant amount of liquid water, which can act as a critical solvent, impacting aerosol growth, ageing and ultimately lifetime in the atmosphere. For example, in order for aerosols to become activated into cloud droplets, they must be able to take up water. This means understanding the interplay between aerosol composition and liquid water content is critical to evaluate the roles aerosols play on climate (Pöhlker et al., 2023) and air quality and human health (e.g., through the formation of haze events (Ge et al., 2024)).

The ability for aerosols to take up or lose water, termed their hygroscopicity, is determined by their chemical composition and driven by thermodynamics. A variety of experimental techniques exist to measure hygroscopic growth and relate it to bulk chemical composition. However, many uncertainties remain in terms of the importance of individual aerosol components on this process. Significant effort has been made to develop thermodynamic models which accurately capture the hygroscopic behaviour of aerosol at a range of relative humidities, temperatures and salt concentrations. However, as mentioned previously, aerosols often become mixed with other particles resulting in complex mixtures. Although thermodynamic models can reasonably constrain simple inorganic salt systems, they often do not include other less abundant species, such as transition metals, or more complex organic components. In part due to the lack of systematic hygroscopicity studies involving these less abundant aerosol species.

In this project, you will use a combination of laboratory-based aerosol flow tube experiments and single particle micro-spectroscopy techniques to study the hygroscopic growth of various mixed-component aerosol systems, in addition to aerosol physicochemical properties. You will also get the opportunity to conduct modelling using thermodynamic models such as E-AIM (Wexler et al., 2002) and ISORROPIA (Fountoukis et al., 2007), to explore the role of seed particle composition on properties such as activity and aerosol liquid water content.

 

Project Objectives:

For this project you will use a combination of aerosol flow tube and single particle micro-spectroscopy experiments to:

• Measure the uptake and loss of liquid water for single and mixed component aerosol systems;
• Characterise the condensed-phase composition of aerosols, and identify how composition changes with the uptake of water;
• Use single particle experiments to evaluate the impact of chemical composition and water uptake on internal aerosol mixing state;
• Compare experimental results with thermodynamic models to evaluate their robustness, especially for more complex aerosol systems.

The research will lead to an improved understanding of hygroscopic growth, and its physicochemical impacts, on mixed component aerosol systems. You will acquire expertise in a range of instrumentation including mass spectrometry, aerosol sizing instruments, and x-ray based micro-spectroscopy (including synchrotron-based techniques) while conducting laboratory measurements. This will also introduce you to common lab practices in atmospheric sciences (e.g., safe handling of vacuum and gas systems, data acquisition, electronics), and engage in collaborations within the Atmospheric, Planetary and Theoretical Chemistry group in the School of Chemistry.

By working with expert investigators, you will receive advanced technical training and enhance your skills for your independent research career. This project will build upon existing expertise at Leeds in aerosol chemistry, by connecting how particles uptake water in the atmosphere. You will use state-of-the-art research infrastructure in the School of Chemistry, including the aerosol flow tube and School of Chemistry Instrumentation facilities. In addition to collaborations at Leeds, there will be opportunities to collaborate with atmospheric scientists in the UK and abroad. Results from this project will be communicated to the scientific community through high-quality publications in leading journals, and at conferences both on the national and international level.

Training:

You will work under the supervision of Dr. Natasha Garner and Prof. Dwayne Heard from the School of Chemistry at Leeds. The supervisors have expertise in conducting laboratory-based experiments to study aerosol multiphase chemistry.

The PhD will provide you with expertise in state-of-the-art atmospheric instrumentation and conducting aerosol flow tube and single particle micro-spectroscopy (e.g., Man et al., 2026) experiments. In addition to gaining technical expertise in the design and conduction of experiments and instrumentation, you will be supported in writing publications and encouraged to attend both national and international conferences. This will help you build your communication skills and help establish a network to assist your career upon graduation. You will also have access to a broad spectrum of training workshops (e.g., scientific writing), in addition to training provided through the National Centre for Atmospheric Science.

Your Profile:

You should have an interest in atmospheric chemistry, air quality, climate and global environmental problems, with a strong background in chemistry or a similar discipline (e.g. physics, engineering, environmental science).

References:

Shrivastava, M., et al. (2017). “Recent advances in understanding secondary organic aerosol: Implications for global climate forcing.” Reviews of Geophysics 55(2): 509-559.

Pöhlker, M.L., et al. (2023). “Global organic and inorganic aerosol hygroscopicity and its effect on radiative forcing.” Nature Communications 14: 6139.

Ge, S., et al (2024). “Characteristics of PM2.5 hygroscopicity and the influences of water-soluble ions during haze events in Beijing.” Atmospheric Environment 322: 120382.

Wexler, A. S. and Clegg, S. L. (2002). “Atmospheric aerosol models for systems including the ions H+, NH4+, Na+, SO42−, NO3−, Cl−, Br−, and H2O.” Journal of Geophysical Research: Atmospheres 107(D14): ACH 14-11-ACH 14-14.

Fountoukis, C. and Nenes, A. (2007). “ISORROPIA II: a computationally efficient thermodynamic equilibrium model for K+–Ca2+–Mg2+–NH4+–Na+–SO42−–NO3−–Cl−–H2O aerosols.” Atmospheric Chemistry and Physics 7: 4639–4659.

Man, R. et al (2026). “Direct observation of core-shell structure and water uptake of individual submicron urban aerosol particles.” Atmospheric Chemistry and Physics 26: 349–363.