The current understanding of climatic influences of cloud formation has been described by the intergovernmental panel on climate change, IPCC, to be 'very low' and an examination of these processes is clearly required.

All cloud droplets form on atmospheric aerosol by taking up water vapour in atmospheric updrafts. The chemical composition of the aerosol determines whether it will activate to become a cloud droplet or not.

Cloud formation is of climatic importance since clouds reflect sunlight back into space and are thus responsible for cooling of the atmosphere. Cloud chemistry also determines the cloud water content and thus controls if a cloud will rain.

Atmospheric aerosol is often coated in organic films that may be one molecule thick. Such monolayers have the ability to lower the surface tension of the droplet and enhance cloud formation (Köhler theory). The atmosphere is oxidising and oxidative degradation of these organic films may increase the surface tension of the organic film and thus prevent cloud formation.

The lab tests whether the atmospheric oxidation is fast enough to compete with the lifetime of aerosol or cloud droplets. Aerosol films are generates on a Langmuir trough and oxidised with gas-phase and liquid phase atmospheric oxidants.

We use the following techniques to study the effect of atmospheric oxidation on aerosol. Principally to investigate the potential for atmospheric oxidation to lower the critical saturation point for cloud formation of an individual aerosol.

• Langmuir trough.

• Neutron Scattering. (www.isis.stfc.ac.uk)

• Optical trapping and Raman analysis of single aerosol. (www.clf.rl.ac.uk)

• Filter analysis of Black Carbon