Multi-species nucleation rates in CLOUD

In the CLOUD experiment at CERN we have been investigating the chemical species that are most important to atmospheric new particle formation. Sulphuric acid plays a key role in aerosol nucleation, but other vapours and ions can strongly enhance the formation rate. Quantifying the contribution of each species and the conditions under which each one is important is a major challenge and requires sophisticated laboratory experiments. The CLOUD chamber, a 3m stainless steel aerosol chamber exposed to a pion beam from the CERN Proton Synchrotron, can create a precisely controlled atmospheric environment over a wide range of temperatures, ionisation states and gas mixtures, while keeping contamination levels extremely low. CLOUD has studied a range of vapour species at atmospheric concentrations, including, in various combinations, sulphuric acid, ammonia, dimethylamine and alpha-pinene. The effect of ions on the nucleation rates has been measured for all species since it is of considerable interest as a possible link between galactic cosmic rays and climate[1]. This work will present an overview of the nucleation rates measured in CLOUD and compare them with atmospheric observations.