Ultrasonic Levitation Studies of Atmospheric Aerosols.

Project highlights

Probing for self-organisation in real atmospheric aerosols for the first time
Sampling & analysing of urban cooking emissions in Birmingham synergistically linked to tailored laboratory experiments incl. refractive index measurements
Employing state-of-the-art laboratory methods to establish the atmospheric importance of aerosol self-organisation

Overview

The project will investigate the potential impact on cloud formation & urban pollution of self-organisation within aerosol particles. Atmospheric aerosols arise from human activity, and influence whether clouds form, how quickly molecules degrade and therefore how long they persist in the atmosphere. Fatty acids & esters are key components of urban aerosols and emitted in substantial quantities from cooking.

So far little consideration has been given as to how these molecules arrange themselves within atmospheric aerosols, and the effects this organisation may have on aerosol properties. Fatty acids are “surface-active” molecules (“surfactants”), possessing water-loving heads & water-hating tails, causing such molecules to accumulate at the outside of water droplets thus determining key aerosol surface properties, such as the ability to nucleate clouds, even at low concentrations. From laboratory experiments, it is known that, within water droplets, surfactants self-organise to form a rich variety of 3–D structures including crystal-like arrays called “lyotropic phases” containing nanoscale sheets, spheres (“micelles”) or cylinders, strongly affecting physical properties including diffusion, viscosity & water uptake. These physical properties are key in an atmospheric context, e.g. for cloud formation & chemical lifetimes of organic molecules, with implications for local weather & human health. Optical properties such as refractive indices are key to establish the impact of aerosol on climate change – this will be addressed in this project through the new link to Dr Gupta’s expertise.

We will collect urban aerosols in Birmingham –with particular focus on cooking emissions– and then study the 3–D structure of atmospheric samples & aerosol proxies using complementary cutting-edge methods with an exciting potential to make a step-change in the understanding of the effects of the aerosol’s internal structure on chemical reactions, cloud nucleation, and the transport speed through the droplets & on atmospheric lifetimes, and thus for their impact on local weather, urban air quality and human health.

Fig. 1. Illustration of urban aerosol components of interest (aerosol proxies and urban particulates to be collected), changes in physical (humidity, temperature, pH) and chemical (exposure to O3/NO3) environments investigated in this project. Ultrasonic levitator used (bottom left) and complex self-organised lyotropic phases reported by us (Pfrang et al., Nature Commun, 2017; see also Milsom et al., 2021a, 2021b, 2022a and 2022b) in ultrasonically levitated droplets with proposed impact on key atmospheric aerosol properties (highlighted in red) & condition-dependent phase changes (highlighted in yellow).

Host

University of Birmingham

Theme

Climate and Environmental Sustainability

Supervisors

Project investigator

Dr. Christian Pfrang, University of Birmingham ([email protected])

Co-investigators

Dr. Ruchi Gupta, University of Birmingham ([email protected])
Dr. Ben Langford, Centre for Ecology and Hydrology (CEH) ([email protected])

How to apply

Each host has a slightly different application process.
Find out how to apply for this studentship.
All applications must include the CENTA application form.
Choose your application route

Methodology

We will collect and analyse urban aerosol samples in Birmingham benefitting from existing infrastructure, expertise and state-of-the-art instrumentation available within GEES at Birmingham. We will then investigate lyotropic phases formed in these atmospheric samples; this work will be complemented by studying well-defined “proxy” mixtures with atmospherically realistic surfactant composition, temperature and humidity, in “bulk” samples of surfactant & water, films and levitated droplets. We will probe the self-organisation using a technique for investigation of nanoscale structure (Small-Angle X-ray Scattering, SAXS), and the viscosity, diffusion & water uptake using complementary methods. Self-organisation of molecules on the surface of droplets will result in direction-dependent refractive indices. Thus, self-organisation will also be studied by measuring optical scattering signal corresponding to light of different polarisation. Scattering signals will be excited using whispering gallery mode and leaky waveguide resonances for improved signal to noise ratio building on Dr Gupta’s expertise. Applying these laboratory techniques for the first time to real atmospheric aerosols collected in Birmingham is an essential step to establish the real-world impact of lyotropic phases. The ultimate aim is to establish the importance of the nanoscale self-organisation within aerosols for atmospheric processes – potentially resolving key unknowns in the behaviour of aerosols, clouds & urban air pollutants.

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.

The student will be trained to carry out field sampling, laboratory experiments and participate in beamtime at large-scale facilities (DLS/MAXIV). S/he will link to Dr Gupta’s group in Chemistry benefitting from local expertise in optical measurement techniques and microfluidics, and networking opportunities.

There will be opportunities to participate in kinetic aerosol modelling in collaboration with the Max Planck Institute for Chemistry, MPIC (Mainz, Germany).

Training on modelling and experimental methods, literature search and scientific writing will be provided incl. weekly supervisory meetings. The student will benefit from expertise within GEES with 15+ permanent staff leading closely related research with opportunities to present research, discuss challenges, collaborate and get an understanding of the broader context. Chemistry offers expertise in interactions, interfaces and sensing with 10 academics working in this theme in addition to recently recruited academics focussing on atmospheric chemistry.

Partners and collaboration

This project is co-developed with the School of Chemistry at Birmingham in anticipation of the upcoming joint move into Birmingham’s new Molecular Science building in 2023. Co-I Dr Gupta is an expert in optical measurement techniques based on refractive index and their integration with (continuous and droplet) microfluidics. She has a PostDoc working on levitation and manipulation of fluidic droplets using sound waves and integration of acoustic levitator with optical detection. This project links very well to the proposed PhD project as well as to Dr Pfrang’s work on ultrasonic levitation of aerosols more generally with strong potential to lead to a long-term strategic link for UoB.

Co-I Dr Langford from the Centre for Ecology and Hydrology (CEH) has extensive experience in field sampling, specifically using state-of-the-art instruments such as PTR-Qi-TOF-MS systems available both at CEH and within GEES. He provides outstanding expertise in field studies synergistically complementing Dr Pfrang’s expertise in laboratory studies of self-organised samples. The MPIC is Dr Pfrang’s project partner on a current NERC grant workpackage on modelling oxidation of self-assembled atmospheric materials with a PostDoc within GEES. Dr Pfrang leads a NERC SPF network on “Air Pollution Solutions for Vulnerable Groups (CleanAir4V)” as well as a £1 million MetOffice SPF grant developing an “Indoor Air Quality Emissions & Modelling System (IAQ-EMS)” (since January 2022 for 37 months) which both include measurements of cooking emissions also harvesting Birmingham’s new “Air Quality Supersite Triplet (UK-AQST)” (Dr Pfrang is a Co-I for UK-AQST) facilities.

Further details

For further information, please contact Dr Christian Pfrang, School of Geography, Earth & Environmental Sciences, University of Birmingham ([email protected]; webpage: https://www.birmingham.ac.uk/staff/profiles/gees/pfrang-christian.aspx).

If you wish to apply to the project, applications should include:

A CENTA application form, downloadable from: CENTA application

A CV with the names of at least two referees (preferably three and who can comment on your academic abilities)

Submit your application and complete the host institution application process via: https://sits.bham.ac.uk/lpages/LES068.htm. and go to Apply Now in the PhD Geography and Environmental Science (CENTA) section. Please quote CENTA23_B17 when completing the application form.

Applications to be received by the end of the day on Wednesday 11^th January 2023.

Additional information for international applicants

All international applicants must ensure they can fulfil the University of Birmingham’s international student entry requirements, which includes English language requirements. For further information please visit https://www.birmingham.ac.uk/postgraduate/pgt/requirements-pgt/international/index.aspx.
Please be aware that CENTA funding will only cover University fees at the level of support for Home-fee eligible students. The University is only able to waive the difference on the international fee level for a maximum of two successful international applicants.

Possible timeline

Year 1

Literature review, training in generic research techniques (e.g. research ethics, project planning & laboratory safety), and subject-specific training in collecting & analysing aerosol samples, learning & applying laboratory-based analytical methods in GEES (aerosol and gas handling, ultrasonic levitation, SAXS, Raman microscopy and complementary techniques) and Chemistry (fabrication of leaky waveguides and applying them for scattering studies). Developing more advanced coding skills in preparation for the modelling component of the project.

Year 2

Continue urban sample collection; optimise extraction methods and characterise composition of urban samples; laboratory experiments on atmospheric aerosol proxies with ultrasonic levitation, in bulk mixtures and thin films; experimental set-up to excite whispering gallery mode resonances in levitated droplets and measure scattering signals; write-up of initial data for an international conference towards the end of year 2 (poster or oral presentation); contribute to beamtime applications at Diamond Light Source and MAXIV, Sweden.

Year 3

Complete urban sample collection; introduce urban samples into laboratory experimental systems and carry out optimised laboratory experiments; participate in beamtime experiments and contribute urban cooking samples; apply optical scattering measurements to complex urban samples; start writing up research papers and PhD thesis; participate at a second international conference towards the end of year 3 (oral presentation if possible).

Year 4: Completion of thesis and writing of papers.

COVID-19

This experimental project includes use of large-scale facilities and will potentially be affected by laboratory and facility closures. All facilities are available in the UK, so no international travel is essential (alternative facilities exist in Europe in case access to UK facilities becomes limiting). Experimental data will be obtained in short beam-time experiments and facilities run Covid-19 resilience programmes (e.g. if no user access is possible, experiments are carried out by mailing in samples). Many experiments can be conducted by a single person even if collaborative experimentation would not be feasible; a substantial proportion of the project will be highly flexible analysis and modelling of experimental data; some experimental data were collected already and back-up field samples are ready for use; interaction with CEH/MPIC can be carried out electronically.