In a study led by the University of Leeds, scientists have solved one of the most long-standing challenges in atmospheric science: to understand how particles are formed in the atmosphere.
Fundamental questions remain about the origin of newly formed atmospheric aerosol particles because data from laboratory measurements have been insufficient to build global models. In contrast, gas-phase chemistry models have been based on laboratory kinetics measurements for decades. Here we build a global model of
Here we build a global model of aerosol formation using extensive laboratory-measured nucleation rates involving sulfuric acid, ammonia, ions and organic compounds. The simulations and a comparison with atmospheric observations show that nearly all nucleation throughout the present-day atmosphere involves ammonia or biogenic organic compounds in addition to sulfuric acid.
A significant fraction of nucleation involves ions, but the relatively weak dependence on ion concentrations indicates that for the processes studied variations in cosmic ray intensity do not significantly affect climate via nucleation in the present-day atmosphere.
The lead scientist on the study, Professor Ken Carslaw, from the School of Earth and Environment at the University of Leeds, said: “This is a major milestone in our understanding of the atmosphere. The CERN experiment is unique, and it has produced data that seemed completely out of reach just five years ago.”
Clouds in the atmosphere consist of tiny droplets, which form when water condenses around small particles in the atmosphere called ‘aerosols’.
Understanding how aerosols are formed is therefore vital for understanding cloud formation — a process that has, until now, been an uncertain quantity in climate models, introducing problems for climate change projections.
For over 30 years, scientists have been able to build computer simulations of atmospheric gases based on measurements of chemical reaction rates made in a laboratory. This capability has been essential to our current understanding of the atmosphere, including the destruction of the ozone layer.
Until now, the same level of understanding has not been possible for aerosol particles in the atmosphere because of the enormous challenges involved in reliably measuring particle formation in a laboratory.
The CLOUD experiment can measure the ‘nucleation’ of new atmospheric particles – that is, when certain molecules in the atmosphere cluster together and grow to form new particles – in a specially designed chamber under extremely well controlled environmental conditions. Nucleation is important because, by current estimates, about half of all cloud droplets are formed on aerosol particles that were created in this way.
Professor Carslaw concludes: “These new results will give us much more confidence in how particles and clouds are handled in global climate models.”