Development of particle size and composition distributions with a novel aerosol dynamics model |
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| Authors: | LIISA PIRJOLA MARKKU KULMALA |
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| Institution: | Department of Physics, University of Helsinki, PO Box 64, FIN‐00014 Helsinki, Finland |
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| Abstract: | An aerosol dynamics model, AEROFOR2, is developed in the context of the BIOFOR project focussing on boreal forest aerosol. It is the second version of a Lagrangian type box model AEROFOR for investigating the formation and growth of particles under clear sky atmospheric conditions. Particles can consist of soluble and insoluble material and the particle population can be externally or internally mixed. AEROFOR2 includes gas phase chemistry and aerosol dynamics, and calculates the number and composition distributions of particles as functions of time. Observed growth rates of the nucleation mode particles after a typical nucleation event are 2–3 nm/h. The model simulations predict that 3·107 molecules cm?3 of insoluble organic vapour and less than 6·106 molecules cm?3 of soluble vapour condensing onto particles are enough to make them grow in good agreement with the observed growth rates. Then the source rate of the organic vapour must be an order of 105 molecules cm?3 s?1, and its saturation vapour density should be below 106 molecules cm?3. If the aerosol was initially an internal mixture of soluble (70%) and insoluble (30%) constituents it transformed to an externally mixed aerosol during the simulation. By applying the externally‐mixed aerosol based on measured soluble volume fractions, it was concluded that the modelled soluble fraction of the nucleation mode was too low in comparison with the measurements, and thus, a part of the condensable organic vapour must be water soluble. |
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