New light from CLOUD on climate change
In a paper published in the journal Nature, the CLOUD experiment at CERN reports on a major advance towards solving a long-standing enigma in climate science: how do aerosol particles form in the atmosphere? It is known that all cloud droplets form on aerosols: tiny solid or liquid particles suspended in the air. However, how these aerosol particles form or “nucleate” from atmospheric trace gases – and which gases are responsible – has remained a mystery.
According to the Intergovernmental Panel on Climate Change (IPCC), aerosol particles and their influence on clouds constitute the biggest uncertainty in assessing human-induced climate change. Understanding how aerosol particles form in the atmosphere is important since in increased concentrations, they cool the planet by reflecting more sunlight and by forming smaller but more numerous cloud droplets. That, in turn, makes clouds more reflective and extends their lifetimes. These poorly-understood processes currently limit the precision of climate projections for the 21st century.
Thanks to CERN expertise in materials, gas systems and ultra-high vacuum technologies, the CLOUD team was able to build a chamber with unprecedented cleanliness. This enabled them to introduce minute amounts of various atmospheric vapours into an initially “pure” atmosphere under carefully controlled conditions, and start unravelling the mystery.
The researchers made two key discoveries. Firstly, they found that minute concentrations of amines can combine with sulphuric acid to form aerosol particles at rates similar to atmospheric observations. Secondly, using a pion beam from the CERN Proton Synchrotron, they found that cosmic radiation has a negligible influence on the formation rates of these particular aerosol particles.