CLOUD-MOTION · CLOUD-MObility, Training and InnOvation Network

CLOUD-MObility, Training and InnOvation Network

CLOUD-MOTION: CLOUD-MObility, Training and InnOvation Network New-particle formation, or nucleation, largely determines the number concentration of ultrafine particles (<100 nm) in the atmosphere, and models predict that approximately half of global cloud condensation nuclei form in this way. Nucleation is therefore critical to aerosol-cloud interactions and climate. Due to the non-linear nature of the processes, competing mechanisms, and the complex variety of chemical compounds that influence nucleation we are still far from a satisfactory level of understanding. Ice nucleation, i.e. the formation of ice in clouds, also plays an important role governing the radiative properties of ice and mixed-phase clouds and influencing precipitation and climate, but only a tiny, poorly understood fraction of atmospheric particles act as heterogeneous ice-nucleating particles (INP). Both of these topics - aerosol nucleation and ice nucleation - are studied with great precision at the CLOUD aerosol and cloud chamber facility at CERN. The experimental data are parametrized to improve air-quality models and climate-change predictions, two topics of highest relevance and timeliness for society. The major research activity of CLOUD-MOTION was to perform three sets of joint experiments at the CLOUD aerosol chamber. The focus of investigations was: a) aerosol nucleation and growth in pristine environments (tropical free troposphere and unpolluted marine environments), b) aerosol nucleation and growth in the polluted atmosphere (urban environments), c) the formation of ice on glassy Secondary Organic Aerosol acting as Ice Nucleating Particles (“glassy SOA as INP”). CLOUD is the world’s first experiment to reach the technical standards required to measure nucleation and growth of aerosol particles under controlled atmospheric conditions in the laboratory. A beamline at CERN allows to simulate the role of galactic cosmic rays for aerosol formation and cloud processes. CLOUD-MOTION was successfully finished on December 31, 2021. The scientific goals of the project were reached. Main conclusions of the project are that a) an important, so far unknown, role for the combination of nitric acid and ammonia was found to cause rapid growth of aerosol particles in urban atmospheres, b) the nitric acid-ammonia-sulfuric acid system is responsible for nucleation and growth of aerosols in the upper troposphere above the Asian monsoon, and c) the molecular steps for nucleation of iodine oxoacids were identified and the role of this process was highlighted for Arctic regions. All early-stage researchers, employed for CLOUD-MOTION, received excellent training at their host institutions as well as within the project network.

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