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TYC@UCL: Particles out of thin air

Professor Hanna Vehkamaki, University of Helsinki

Atmospheric aerosol particles affect human health, visibility and climate.  Cloud formation in our atmosphere always involves particles as cloud condensation nuclei.  The direct scattering effect together with the influence via clouds constitute the largest uncertainty in predicting future climate. Not all the particles are emitted in the air in solid or liquid form: it is estimated that approximately half of modern-day cloud condensation nuclei originate from atmospheric nucleation born in the air from condensable vapours.  In many (but not all) atmospheric locations, the strongest candidate for a particle forming vapour is sulphuric acid, but other vapours are needed to assist the process.  We have used first principles computational chemistry method to study the stability of charged and neutral sulphuric acid clusters containing also ammonia, dimethylamine and water. Using the computed cluster properties in a cluster size distribution dynamics model we are able match the nucleation rates observed in the CLOUD chamber in CERN.  Comparison of theoretical results with mass spectrometric data reveals that clusters are  affected by the instrument, and thus we currently  study cluster also fragmentation inside mass spectrometers, where thermodynamic equilibrium is not a valid assumption.

Friday 13 October 2017
Time: 1-2pm
Venue: Physics Building room E7
Contact: Karen Stoneham
Tel: 020 76797306
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    Hanna Vehkamaki
    Professor in computational aerosol physics

    Hanna Vehkamäki is a professor in computational aerosol physics in the Division of Atmospheric Sciences, Department of Physics at the University of Helsinki.  She leads a research group of   around 10 people whose research focuses on molecular level modeling of atmospheric cluster and  particle formation, as well as ice nucleation.  She has an MSc (1994) and PhD (1998) in Theoretical Physics from the University of Helsinki and was a Research Fellow at University College London between 1998-1999.  Hanna received an ERC stating grant in 2009 and an ERC advanced grant in 2015.  Hanna has also received an award for her equal opportunities work in academia.

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