CLOUD experiment

In 2014, CLOUD researchers presented newer experimental results showing an interaction between oxidised biogenic vapours (e.g., alpha-pinene emitted by trees) and sulphuric acid.

Ions produced in the atmosphere by galactic cosmic rays enhance the formation rate of these particles significantly, provided the concentrations of sulphuric acid and oxidised organic vapours are quite low.

This new process may account for seasonal variations in atmospheric aerosol particles, which are being related to higher global tree emissions in the northern hemisphere summer.

The experiments show that sulfuric acid and oxidized organic vapors at low concentrations reproduce suitable particle nucleation rates.

The nucleation mechanism used on global aerosol models yields a photochemically and biologically driven seasonal cycle of particle concentrations and cloud formation in good agreement with observations.

The nucleation process of water droplets/ice micro-crystals from water vapor reproduced in the CLOUD experiment and also directly observed in the Earth atmosphere do not only involve ions formation due to cosmic rays but also a range of complex chemical reactions with sulfuric acid, ammonia and organic compounds emitted in the air by human activities and by organisms living on land or in the oceans (plankton).