Overview

Project Highlights:

  • Probing for self-organisation in real atmospheric aerosols for the first time
  • Sampling & analysing of urban cooking emissions in Birmingham is synergistically linked to tailored laboratory experiments
  • 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.

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) in ultrasonically levitated droplets with proposed impact on key atmospheric aerosol properties (highlighted in red) & condition-dependent phase changes (highlighted in yellow).

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.

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

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 visit CEH benefitting from local expertise in atmospheric sampling and networking opportunities. There will be opportunities to participate in kinetic aerosol modelling in collaboration with the Max Planck Institute for Chemistry.

Training on literature search and scientific writing will be provided during weekly supervisory meetings. S/he will benefit from expertise within GEES with 10+ academics leading closely related research with opportunities to present research, discuss challenges, collaborate and get an understanding of the broader context of this project.

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 (aerosol and gas handling, ultrasonic levitation, SAXS, Raman microscopy and complementary techniques).

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; 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; 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.

 

Partners and collaboration (including CASE)

This project is co-developed with the Centre for Ecology and Hydrology (CEH) building on a current joint NERC grant on impact of air pollution on insect communication. Co-I Dr Langford 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. Co-I Dr Shi is science coordinator of the Atmospheric Pollution and Human Health in a Chinese megacity (APHH-China) programme and coordinated two successful field campaigns in Beijing. Drs Langford and Shi thus provide outstanding expertise in field studies synergistically complementing Dr Pfrang’s expertise in laboratory studies of self-organised samples.

Further Details

For further information, please contact Dr Christian Pfrang, School of Geography, Earth & Environmental Sciences, University of Birmingham (c.pfrang@bham.ac.uk; 0121 414 5519; webpage: https://www.birmingham.ac.uk/staff/profiles/gees/pfrang-christian.aspx).