1. School of Earth and Environment INSTITUTE FOR CLIMATE & ATMOSPHERIC SCIENCE The UKCA aerosol model Ken Carslaw Graham Mann (NCAS, School of Earth & Environment, Univ. of Leeds) Carly Reddington, Matt Woodhouse, Sandip Dhomse, Kathryn Emmerson, Kirsty Pringle, Dominick Spracklen, Anja Schmidt, Lindsay Lee (School of Earth & Environment, Univ. of Leeds) Acknowledgements to the rest of the UKCA team Colin Johnson, Nicolas Bellouin, Mohit Dalvi Philip Stier, Rosalind West, Zak Kipling (Hadley Centre, UK Met Office) (University of Oxford) Luke Abraham, Paul Telford, Peter Braesicke, Alex Archibald, John Pyle (University of Cambridge)

2. Overview What is UKCA aerosol? What research is currently underway? Towards the best evaluated aerosol-climate model in the world Current lines of development What are the development needs and opportunities for community effort?

3. UKCA: The UK Chemistry and Aerosol model o Collaboration between NCAS (Leeds and Cambridge) & Met Office since 2005 o Aerosol-chemistry sub-model in the Unified Model environment for a range of applications (climate, air quality, Earth system science, weather) o Fully coupled tropospheric and stratospheric chemistry schemes o Multi-component aerosol microphysics o Cloud drop concentrations o Direct & indirect radiative effects for fully coupled composition-climate simulations

4. Aerosol representation in climate models IPCC climate models have mostly included only a simple representation of aerosols Mass of aerosol components is only advected quantity (e.g., sulphate, black carbon, dust, sea-salt mass) Assumed size distribution Chemical components not mixed Direct aerosol forcing: Use composition-dependent mass scattering efficiency (or assume a fixed size distribution) Indirect forcing: Use empirical cloud drop—aerosol relations Important aerosol types (e.g. organics, nitrate) omitted.

5. Processes control size & composition Coagulation Particle Size Emission of gas phase precursors Nucleation Emission of primary particles Dry Deposition cloud processing In-cloud oxidation Wet Deposition ~1.E-9 m Activation of CCN ~50.E-6 m Involatile and semi-volatile gas phase oxidation products Condensation In-air oxidation Uptake to clouds

6. Nucleation produces cloud-forming aerosol Growth of new particles to cloud condensation nuclei ~ CCN size Global Model Observations Spracklen et al., ACP, 2006

7. Nucleation is a global source of cloud-forming aerosol CCN from nucleationCCN from primary emissions 39% of low cloud-level CCN are from nucleation, 61% from primary particles Merikanto et al., ACP 2009 Merikanto et al., ACP, 2009

8. CLASSIC and UKCA compared CLASSICUKCA Transported particle types Associated with emissions (sulphate, biomass, etc) Defined by microphysics (Aitken, accumulation, etc) Size distributionPrognostic m Fixed size N derived from m and size Prognostic N, m Variable size Log-normal modes Mixed composition NoYes ChemistryOffline oxidantsCoupled chemistry Cloud drop number From massFrom size, N, mixed composition Particulate tracers1327 (min 24)

9. A fairly complex, but fast, microphysical scheme Bellouin, Mann et al., ACP, 2013

10. UKCA aerosol references Mann GW; Carslaw KS; Spracklen DV; Pringle KJ; Lee LA; Manktelow PT; Woodhouse MT; Schmidt A; Emmerson KM; Reddington CL; Chipperfield MP; Pickering SJ; Ridley DA; Merikanto J; Korhonen H; Schwarz JP; Breider TJ (2012) Intercomparison of modal and sectional aerosol microphysics representations within the same 3-D global chemical transport model, Atmospheric Chemistry and Physics, 12, pp.4449-4476. Mann GW; Carslaw KS; Spracklen DV; Ridley DA; Manktelow PT; Chipperfield MP; Pickering SJ; Johnson CE (2010) Description and evaluation of GLOMAP- mode: a modal global aerosol microphysics model for the UKCA composition- climate model, GEOSCI MODEL DEV, 3, pp.519-551. Mann et al., Description and evaluation of the UKCA aerosol scheme in the HadGEM climate model, to be submitted to GEOSCI MODEL DEV, 2013. Scientific application papers:

11. Importance of resolving microphysics: CCN response to DMS emissions Bellouin, Mann et al., ACP, 2013 Old aerosol scheme overestimates CCN response to DMS emissions because it can only add particle number

12. Importance of resolving microphysics: Indirect forcing CLASSIC UKCA Bellouin, Mann et al., ACP, 2013 Indirect forcing in UKCA is less than old scheme because nucleation generates higher CCN in pre-industrial.

13. What can UKCA-aerosol do?

14. Tropospheric chemistry and aerosol DMSSO2Sulphate Elemental C Organic CNaCl Mann et al., Upcoming UKCA- aerosol documentation paper in GMD, 2013

15. Tropospheric aerosol microphysics Global CCN CCN seasonal cycle at Cape Grim Global CCN evaluation Mann et al., Upcoming UKCA- aerosol documentation paper in GMD, 2013

16. Tropospheric aerosol radiative properties Bellouin, Mann et al., ACP, 2013 For aerosol optical depth, UKCA is as good, or better, than old scheme

17. Total (direct + indirect) forcing West, Stier et al., 2013 Mechanistic cloud drop number calculation  forcing

18. Model CN CN > 150nm CN > 250nm Observations CN CN > 150nm CN > 250nm ++++++ Balloon measurements of number concentration at Laramie, Wyoming (Deshler et al, 2003) 1 cm -3 Mar 1991Mar 1992 3 months before Pinatubo9 months after Pinatubo Stratospheric aerosol Emmerson, Dhomse et al., in prep 2013 Investigating radiative, chemical and dynamical effects of Pinatubo eruption

19. What research is currently underway?

20. Research currently underway PhD Douglas Hamilton Leeds Met Office Folberth Natural aerosol feedbacks in the Earth system PhD Leighton Regayre Leeds Met Office Booth Aerosol uncertainty and climate impacts PhD Steven Turnock Leeds Met Office – Haywood/Spracklen Mitigation of climate change by air pollutants ACCACIA Leeds, Manchester, York, BAS, UEA, Met Office Aerosol-cloud-climate effects in the Arctic ACID-PRUF Manchester, Oxford, Leeds, Exeter, Met Office Consortium to reduce the uncertainty in indirect forcing ASCI Leeds, Met Office High resolution (1km) aerosol-cloud coupled version of UKCA SAMBBA Exeter, Manchester, Leeds, Met Office, Reading South American Biomass Burning Analysis GASSP Leeds, Oxford, Manchester Global Aerosol Synthesis and Science Project PEGASOS EU Leeds, Edinburgh, CEH +++ AQ-climate interactions: 60y hindcast and 50y projection Semi-direct effect Reading Aerosol absorption and the semi-direct effect Volcanic Exeter and Leeds Various volcanic studies Geoengineering Exeter and Leeds Various geoengineering studies

21. Aiming to become the best understood and evaluated model in the world

22. Lots of previous evaluation of GLOMAP models Global CCN Global particle number Black carbon Global AMS organics Stratosphere Dozens of datasets to evaluate UKCA

23. Projects dedicated to model improvement AEROS (2010-2013) Aerosol Model Robustness and Sensitivity Study - Techniques for global aerosol model uncertainty analysis Leeds and Oxford GASSP (2013-2016) Global Aerosol Synthesis and Science Project - Constraining model processes Leeds, Oxford, Manchester + 11 data partners AEROCOM – Aerosol Comparison of Models Project - Leading the microphysics model intercomparison and evaluation

24. Quantifying the magnitude and causes of uncertainty Model Intercomparison Projects focus on diversity Doesn’t lend itself to model improvement Uncertainty attributable to processes would be a valuable addition mean +1  -1  Emission size Wet scav rate SOA burden Nucleation rate Best model “Real” discrepancy Observations Development path

25. AEROS: A new level of statistical information Lee et al., ACP, 2011, 2012 Model emulators enable a Monte Carlo-type sampling of the model uncertainty space  pdf of outputs  full variance-based uncertainty analysis

26. Sources of aerosol uncertainty Global mean of  CCN /CCN Global mean of  CCN /CCN Variance decomposition tells you how much each parameter contributes to the uncertainty in any location Lee et al., submitted ACP, 2013

27. The Global Aerosol Synthesis and Science Project (GASSP!) GASSP project will synthesise 20 years of data with UKCA to understand causes of bias NASA AIRBORNE TROPOSPHERIC CHEMISTRY FIELD CAMPAIGNS (1983-2006)

28. Multi-model assessment (AEROCOM) Graham Mann is leading the AEROCOM microphysics model intercomparison 12 models In parallel, analysing multiple models

29. Future development

30. ASCI - High resolution aerosol-cloud coupled UM Image courtesy Paul Field & Adrian Hill MODIS UM Collaboration of Leeds and Met Office (Field/Shipway/Hill) to develop a nested UKCA aerosol-cloud model down to 100m resolution.

31. Development needs and opportunities for community effort (1/2) Use the model! Models improve when they are used Lots of support/expertise: Mohit Dalvi (JWCRP), Luke Abraham (NCAS), Graham Mann (NCAS) Model development Secondary organic aerosol Aqueous (cloud) chemistry and wet removal Dry deposition of aerosol and precursors Sub-grid processes Emissions and sub-grid emissions

32. Development needs and opportunities for community effort (2/2) Community expert elicitation Uncertainty analysis depends on expertise and advice Model development path more connected to the community Idea in GASSP is to put ongoing data synthesis/evaluation results online and invite suggestions/collaboration Establish closer connection to other models, lab studies etc. Extension to chemistry?

33. Lots of models! TOMCAT global CTM GLOMAP-bin aerosol module Sectional (bin) aerosol GLOMAP-mode aerosol module Modal aerosol HadGEM UM GLOMAP-mode aerosol module Observations Field campaigns Climate Prediction UKCA in HadGEM2/3 Future UK ESM GLOMAP-mode aerosol module Earth System coupling ECMWF-IFS GLOMAP-mode aerosol module Operational forecasts NWP UM GLOMAP-mode aerosol module Weather NWP resolution AQ-UM GLOMAP-mode aerosol module Air quality Boundary conditions (PLANNED) Lots of exciting opportunities to use and develop models

34. UKCA-related meetings March The UK Composition-Climate Interaction Meeting (2011 Leeds, 2012 Oxford, 2013 Cambridge) Sept UKCA aerosol users meeting UKCA+ Early Career Network Douglas Hamilton, Leeds Steve Rumbold, Met Office d.hamilton@leeds.ac.uk

35. Aerosol-chemistry coupling in climate mode Basic tropospheric scheme: 8 emitted species, 46 species, 102 gas-phase reactions, 27 photolysis reactions. Ox, HOx and NOx chemical cycles and the oxidation of CO, ethane and propane. Aer-chem extension: Sulphur chemistry. Simple monoterpene oxidation for SOA. Standard “IsopTrop/CheT” tropospheric scheme: As above plus Mainz Isoprene Mechanism. Aer-chem extension: As above but rates match as in TOMCAT-GLOMAP. Not yet included isoprene-derived SOA Standard “StratChem/CheS” stratospheric scheme Simpler tropospheric chemistry beneath more complex stratospheric scheme. 5 heterogeneous reactions based on UKCA-MODE surface area concentration. Aer-chem extension: Stratospheric sulphur scheme including COS. Extended Tropospheric Chem (ExtTC): 63 tracers, 198 reactions. BVOCs (isoprene, terpenes, methanol, acetone) computed interactively. SOA sub-model: Includes isoprene, terpenes (lumped), aromatics (lumped), C4+-alkanes (lumped), ethene, propene, MEK, MVK, low-reactivity organic nitrate compounds, organic acids (formic, acetic), and semi-volatile SOA precursors. An extension to HadGEM2-ES. Not yet coupled to GLOMAP-mode (old CLASSIC aerosol scheme) Regional Air Quality scheme in UM (RAQ): Not yet coupled to GLOMAP-mode