Self-Organisation in Urban Atmospheric Aerosols?

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.