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Modelling the evolution of the key properties

Modelling the evolution of the key properties controlling SSA from near sources to regional scales. Maria Grazia Frontoso K. Carslaw, G. Mann, D. Spracklen. Institute for Climate & Atmospheric Science (ICAS) University of Leeds. ADIENT meeting, 02 April 2009, Manchester.

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Modelling the evolution of the key properties

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  1. Modelling the evolution of the key properties controlling SSA from near sources to regional scales Maria Grazia Frontoso K. Carslaw, G. Mann, D. Spracklen Institute for Climate & Atmospheric Science (ICAS) University of Leeds ADIENT meeting, 02 April 2009, Manchester

  2. OBJECTIVES Quantifying the level of complexity required to capture observed temporal/spatial changes in SSA and what is lost by simplification in a climate model. Test of the UKCA model VS more complex size-resolved bin models. BENCHMARK DATASETS • Black Carbon: mass, size distr, mixing state from SP2 • Single Scatter Albedo

  3. GLOMAP GLObalModelofAerosol Processes

  4. GLOMAP

  5. dN dlogr log(r) GLOMAP-bin & GLOMAP-mode dN dlogr GLOMAP bin • Size & composition-resolved in 2-moment • multi-component bin scheme • Species: SU, SS, BC, OC into 2 distributions • (insoluble & soluble) • Include boundary layer nucleation log(r) GLOMAP mode • Size & composition-resolved in 2-moment • multi-component modal scheme • Species: SU, SS, BC, OC in 7 modes • (HAM/M7 scheme) • Implementing dissolution module • for NH3, HNO3 (NO3 & NH4 components in • soluble modes) BOTH MODELS HAVE COMPARABLE AEROSOL PROCESSES

  6. BLACK CARBON in GLOMAP (1) • EMISSIONS • - anthropogenic sources • (fossil fuel & biofuel BC/OC, Bond et al. 2004) • - wildfire sources • (BC/OC following GFED emissions in Van Der Werf 2003) • BC is treated as externally mixed • BC in GLOMAP-bin is 2 distributions with 20 size bins: • - insoluble • - soluble/mixed • BC in GLOMAP-mode is in 4 modes: • - insoluble Aitken • - soluble Aitken • - soluble accumulation • - coarse accumulation

  7. BLACK CARBON in GLOMAP (2) Ageing is treated by transferring number and mass of insoluble particles to the soluble distribution at a rate given by 1molecule coating of H2SO4 Soluble distribution Insoluble distribution Soluble BC is more efficiently removed by dry and wet deposition processes, and have a shorter residence time Amount of BC: Insoluble VS Soluble BC emitted in insoluble distribution

  8. Aircraft observations & global models??? RESOLUTION Not a winning combination • Vertical variability • Horizontal variability

  9. Aircraft observations & global models??? More reasonable averaging data taking into account the vertical variability

  10. Slope = 1.01 R = 0.99 BC mass - MODE BC mass - BIN BC mass: good agreement BIN & MODE GLOMAP-bin GLOMAP-mode DBC mass < 0.1 mg/m3

  11. BC mass against SP2 observations Gavin McMeeking, SP2 data Slope = 1.76 R = 0.66 A general overestimation B A • Two different trends? • A  underestimation • B  overestimation

  12. FLEXTRA: BC agespectrum Andreas Stohl, FLEXTRA products • Emissions based mostly on EDGAR 2000 plus better North American • emissions plus a few other modifications • Four anthropogenic tracers: • CO – passive • NOx – passive • SOx – dry and wet deposition • BC – dry and wet deposition • Two biomass burning tracers: CO and BC (latter again dry and wet • deposition) • Output resolution: 0.25 degree over Europe • BC agespectrum (purely passive and aerosol-like tracers) interpolated • along the flight-path • Mass of BC in 20 bins (1 day, 2 days, ..... 20 days)

  13. FLEXTRA: BC agespectrum Andreas Stohl, FLEXTRA products Y = 2.6 + 1.1 X R = 0.92 BC age as been calculated as average of BC aerosol and BC tracers age

  14. FLEXTRA: BC agespectrum Fresh BC more than 60% of BC mass has less than 1 day

  15. FLEXTRA: BC agespectrum Aged BC more than 50% of BC mass has more than 13 days

  16. BCmeas/BCmod against BC age • Model overestimate BC mass • when BC age < 7 days • Model underestimate BC mass • when BC age > 7 days too strong removal of aged BC? too strong emissions of fresh BC?

  17. Sensitivity runs Too strong emissions of fresh BC? BC is only emitted in insoluble Aitken mode BC emitted in 80% as insoluble Aitken and 20% as isoluble Aitken Too strong removal of aged BC? Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 1 moleculecoating of H2SO4 Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 10 moleculecoating of H2SO4

  18. BC mass against SP2 observations Slope = 1.76 R = 0.66 Slope = 1.49 R = 0.69 • BC mixing state? • BC size distributions? • SP2  Black Carbon • Emissions  Element. Carbon

  19. Insoluble vs soluble/mixed BC Fraction of Insoluble BC mass Standard runs New runs 50  27% Fresh BC decrease factor 2 6  30% Aged BC increase factor 5

  20. SSA: -bin, -mode against observations Megan Northway, SSA data GLOMAP-mode vs GLOMAP-bin GLOMAP-bin vs observations Slope = 1.006 R = -0.3 Slope = 1.00 R = 1.00

  21. Which is the role of RH on SSA? • In some cases, ECMWF RH is notcorrect • Sub-grid RH variations: resolution issue? • Increase in RH  increase in SSA

  22. Which is the role of RH on SSA? Model underestimate SSA when underestimate RH Model overestimate SSA when overestimate RH RH can constrain the calculation of SSA

  23. SSA forced with “real” RH Y = 0.882 X R = 0.69 • RH plays a role on SSA… • … not enough to reduce the discrepancies

  24. What controls SSA variations with RH? DSSA not linear with DRH DSSA not linear with fraction of soluble BC

  25. Future investigations • How the model performs in case of high internally mixed BC? • Does it affect SSA? • How the model performs against the size distributions? • Is the mass quite right but the size wrong? • Can we tune the emissions also for the size? • New parameterizazions needed? • Looking at CO & BC  identify BC sources • Is the model resolution an issue for that? • Look at SP2 measurements for mixing state & size distribution • Runs at higher resolution: 1x1 degree • Zoom over UK

  26. DELIVERABLE (W.P.4) • UKCA 1-year simulation to compare with GlobAerosol (2004) • Domain: Europe • Spatial resolution: 2.8x2.8 degrees • Temporal resolution: daily & hourly resolutions • SSA & AOD at 870 and 670 nm • Aerosol composition/type • Effective radius can be also provided

  27. Conclusions • The aerosol sectional bin scheme agrees well with • the modal one for BC mass (slope = 1.01, R = 0.99) • and SSA values (slope = 1.00, R = 0.99) • BC age & ratio insol/sol BC influence • the total amount of BC. • Solubility is driven more by ageing than emissions • General overestimation of BC over Europe • predicted by GLOMAP. More investigations required • looking at BC mixing state and size distributions • RH plays an important role and can constrains • the calculation of SSA • Higher resolution required for the sug-grid RH variations

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