ITN CLOUD

Duration: 2008-2012

Contact: Urs Baltensperger, urs.baltensperger@psi.ch

CLOUD (cosmics leaving outdoor droplets) is an experiment that uses a 3-m stainless-steel chamber at CERN to study the possible link between galactic cosmic rays and cloud formation. Current experiments are designed to better understand aerosol nucleation process (i.e. the formation of new particles from condensing vapors) to provide reliable aerosol physics for climate models. These data will help to quantify the direct and indirect radiative effects of aerosols on climate, which are recognized as the largest source of uncertainty in climate forcing contributed by mankind.

The CLOUD experiment is funded by the EU (Marie Curie Initial Training Network "CLOUD ITN") and involves an interdisciplinary team of scientists from 18 institutes in 9 countries, comprised of atmospheric physicists, solar physicists, and cosmic-ray and particle physicists.

Our contribution to the project are the development and employment of instruments for the measurement of

• particle size distributions (nano-SMPS, CPC battery, and laminar diffusion tube)
• low precursor gas concentrations (such as ammonia and dimethylamine)

In a recent paper published in Nature, the CLOUD collaboration presents measurements of the formation of new particles from sulphuric acid, ammonia and water vapors. The enhancement of atmospheric aerosol nucleation from galactic cosmic rays has also be characterized and the paper presents measurements of the chemistry and growth of newly-formed clusters from single molecules up to stable aerosol particles.