Nucleation of Atmospheric Aerosols

Aerosol particles are important constituents of the Earth’s atmosphere. They play a vital role in the lower atmosphere by affecting the Earth’s radiation balance through the scattering of solar radiation. They also have other highly significant consequences, including detrimental effects on human health. Secondary aerosol particles form by condensation of molecules in the atmosphere. However, the mechanism of this process is very poorly understood and is one of the fundamental unknowns in atmospheric chemistry.

Sulfuric acid has been identified as a critical component but neither it, nor its combination with water, is sufficient to explain the rate of new particle nucleation. At least one additional component is necessary and small organic bases, such as methylamine and dimethylamine, have recently been suggested as prime suspects. To understand how small organic amines might combine with sulfuric acid to initiate the growth of aerosols, it is critical to know how these molecules interact with each other at the molecular level and how this interaction develops into a sustainable intermolecular network, as found in an aerosol particle. This is the target of this studentship. The molecular ingredients will be brought together, molecule-by-molecule, and their interactions will be probed using infrared spectroscopy. The focus will be on the interaction between sulfuric acid molecules and the small amines likely to be significant in the atmosphere, methylamine and dimethylamine. Water molecules can also be added to establish the importance of ternary nucleation.

We will use a novel approach in which molecules are combined inside nanodroplets of liquid helium. As well as providing a nanoscale trap, the helium acts as the transmitter of spectroscopic signals: helium atoms evaporate every time spectroscopic absorption takes place by the molecules inside the nanodroplet, and this loss of helium from the droplet provides our signal. We are international leaders in this technique but it has not previously been used to address problems in environmental science. The student will deliver new information on the fundamental mechanism of aerosol formation. These data are critical in fixing parameters in numerical models of aerosol formation rates, which will in turn feed into global climate models.

Superfluid helium nanodroplets provide an inert, cold and gentle environment in which to trap and assemble molecules into larger structures. This makes it possible to follow an incipient nucleation event, molecule-by-molecule. Infrared spectra will be recorded via a signal depletion technique which is well established in our laboratory. This technique combines IR absorption with mass spectrometry and enables us to use mass-selective detection scheme to extract size-specific information. The spectra will be interpreted using quantum-based simulation techniques.

The principal experimental challenge is to add a gas delivery and pickup cell system to our existing apparatus which can cope with the corrosive effects of sulfuric acid vapour. This will require some modification of the gas delivery lines, the pickup cell design, and the independent pumping of the sulfuric acid pickup cell to minimise leaks into the main vacuum system.

We have received strong support from Andreas Kürten of the Institute for Atmospheric and Environmental Sciences, Goethe-University, Frankfurt, to proceed with these studies. Andreas’s work is directly concerned with the nucleation of new aerosol particles and involves both laboratory studies (e.g. cloud chamber measurements) and field work.

Entry requirements
Applicants are required to hold/or expect to obtain a UK Bachelor Degree 2:1 or better in a relevant subject. The University of Leicester English language requirements apply where applicable.

How to apply
The online application and supporting documents are due by Thursday 25th April 2019.

Any applications submitted after the deadline will not be accepted for the studentship scheme.

References should arrive no later than Monday 29th April 2019.

Applicants are advised to apply well in advance of the deadline, so that we can let you know if anything is missing from your application.

Required Materials:
1. Online application form
2. Two academic references
3. Transcripts
4. Degree certificate/s (if awarded)
5. Curriculum Vitae
6. English language qualification (if English is not your first language)

Applications which are not complete by the deadline will not be considered for the studentship scheme. It is the responsibility of the applicant to ensure the application form and documents are received by the relevant deadlines.

All applications must be submitted online, along with the supporting documents as per the instructions on the website.

Please ensure that all email addresses, for yourself and your referees, are correct on the application form.