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. Black Carbon: mass, size distr, mixing state from SP2 Single Scatter Albedo BENCHMARK DATASETS

3. GLOMAP GLO bal M odel of A erosol P rocesses

4. GLOMAP

5. GLOMAP-bin & GLOMAP-mode dN dlogr log(r) dN dlogr BOTH MODELS HAVE COMPARABLE AEROSOL PROCESSES Size & composition-resolved in 2-moment multi-component bin scheme Species: SU, SS, BC, OC into 2 distributions (insoluble & soluble) Include boundary layer nucleation GLOMAP bin 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)

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) Soluble distribution Insoluble distribution BC emitted in insoluble distribution Ageing is treated by transferring number and mass of insoluble particles to the soluble distribution at a rate given by 1 molecule coating of H 2 SO 4 Amount of BC: Insoluble VS Soluble Soluble BC is more efficiently removed by dry and wet deposition processes, and have a shorter residence time

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

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

10. BC mass: good agreement BIN & MODE Slope = 1.01 R = 0.99 BC mass - BIN BC mass - MODE BC mass < 0.1 g/m 3 GLOMAP-binGLOMAP-mode

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

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

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 emissions of fresh BC? too strong removal of aged BC?

17. Sensitivity runs Too strong emissions of fresh BC? Too strong removal of aged BC? BC is only emitted in insoluble Aitken mode BC emitted in 80% as insoluble Aitken and 20% as isoluble Aitken Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 1 molecule coating of H 2 SO 4 Ageing is treated by transferring number and mass of insoluble particles to corresponding soluble mode at a rate given by 10 molecule coating of H 2 SO 4

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 Fresh BC Aged BC Standard runsNew runs 50 27% 6 30% decrease factor 2 increase factor 5

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

21. Which is the role of RH on SSA? RH meas (%)RH mod (%) 56.450.3 59.247.3 62.748.2 5847.4 62.849.4 46.748.7 43.654.4 35.347.3 43.647.6 10.148.3 SSASSA+RHmeas 0.9440.950 0.9550.962 0.9550.972 0.9330.952 0.9350.959 0.9400.939 0.9240.919 0.9100.904 0.9090.907 0.9090.913 In some cases, ECMWF RH is not correct Sub-grid RH variations: resolution issue? Increase in RH increase in SSA

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

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

24. What controls SSA variations with RH? SSA not linear with RH SSA 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. 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 DELIVERABLE (W.P.4)

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