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Coupled aerosol microphysics and multiphase halogen modelling

Coupled aerosol microphysics and multiphase halogen modelling. Doug Lowe, Dave Topping, Gordon McFiggans University of Manchester ( g.mcfiggans@manchester.ac.uk ). Multiphase Halogen Chemistry.

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Coupled aerosol microphysics and multiphase halogen modelling

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  1. Coupled aerosol microphysics and multiphase halogen modelling Doug Lowe, Dave Topping, Gordon McFiggans University of Manchester (g.mcfiggans@manchester.ac.uk)

  2. Multiphase Halogen Chemistry Chemistry scheme based on the scheme of Pechtl et al (ACP, 2006) – with adaptations to condensed-phase scheme to accommodate PD-FiTE thermodynamics core.

  3. Lower particle number: no chemistry effect Higher particle surface area: increased chemical- exchange rates between gas- and condensed-phases Lower particle volume: slower condensed-phase reactions and lower particulate chemical source term Remote marine testcases – aerosol initialisation 3 methods of generating discrete aerosol size distributions from continuous distributions: 1) Preserve particle number and volume (N/V) 2) Preserve particle number and surface area (N/S) 3) Preserve particle surface area and volume (S/V) S / V N / S N / V NUMBER SURFACE AREA VOLUME Quasi log-normal seasalt mode (after Toyota et al., GRL, 2001)

  4. Organisation of Modelling Studies • Analysis: • Determine influence of initialisation assumptions. For this we will use fixed deposition rates • Determine influence of deposition rate parameterisations.

  5. Size resolution dependence of aqueous species 1 bin per mode: Photochemistry leads to acidification of both modes. Bisulphate dissociation decreases in non-seasalt mode. Diurnal nitrate & sulphate in both modes. Diurnal chloride, bromide & iodide cycling in both modes. 16 bins per mode: Even greater complexity in size segregated composition for all species Further increased structure in composition 4 bins per mode: More complex size segregated composition for all halogen and non-halogen species. Higher resolution exposes increased structure in composition

  6. Influence of Aerosol Initialisation (3/5) Seasalt plus single-bin non-seasalt; fixed turnover rate

  7. Influence of Aerosol Initialisation (4/5) Seasalt plus single-bin non-seasalt; fixed turnover rate

  8. Influence of Deposition Scheme (1/3) Seasalt plus single-bin non-seasalt

  9. Influence of Deposition Scheme (3/3) Seasalt only; offline volumetric averaged turnover rate – 1-bin lifetimes of 0.56 days

  10. Loss rates for each cycle

  11. Conclusions Condensed-phase: A high aerosol size-resolution is necessary to capture variations in sea-salt composition. Gas-phase: Differences in gas-phase chemistry between different aerosol size-resolutions appear to be primarily due to microphysical changes, not changes in condensed-phase chemistry. Choice of initialisation scheme is important for low-resolution models – aerosol surface area and volume must be conserved to accurately capture aerosol influence on gas-phase chemistry. Accurate on-line calculation of size-resolved aerosol deposition and emission rates are important for studying gas-phase chemistry – this is not possible with a low particle size resolution.

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