Dry Deposition Oliver Wild Lancaster Environment Centre, Lancaster University, UK Co-Is: Lisa Emberson (SEI, Univ. York) Dominick Spracklen (Univ. Leeds) PDRA: Catherine Hardacre ACITES Network Meeting, York, 9-10 th January 2013

Why Focus on Dry Deposition? Dry deposition links atmosphere and biosphere – Vital for budgets of many atmos. constituents (O 3, NO y, SO 2, aerosol…) – Vital for input of nutrients/pollutants/oxidants to vegetation, soils – Key component of wider climate and Earth System feedbacks – Policy-relevant implications for air quality, ecosystem health, crops… Deposition is poorly represented in current models – Strong observation/theoretical experience in UK community (CEH, SEI) – Model implementation/development has not kept pace with this A missed opportunity for the UK community? – Timely: metrics for deposition required for developing fully-coupled UK ESM, e.g, for implementing JULES in UKCA/HadGEM

Why Focus on Dry Deposition? Current models do not represent key processes well – Dependence on land surface, vegetation, meteorology… – Heterogeneity of surface (scale effects) Key uncertainty in budget terms (esp. for O 3, aerosol) – Poorly characterised from an atmospheric perspective! Important for Earth System Modelling – Key process for land-surface/atmosphere interactions – Necessary for representation of many ES/climate feedbacks Accommodating new process understanding – Exchange processes: deposition and emission not always separable – Interactions with wet deposition, biogenic emissions, PBL met.

Dry Deposition Processes 1. Turbulent transport through atmosphere 2. Molecular diffusion through laminar sub-layer 3. Uptake on surface by adsorption, followed by dissolution or reaction (depends on surface type: vegetation, soil, water, light, etc.) R a Aerodynamic resistance R b Laminar resistance R soil Soil resistance R can In-canopy resistance R cut Cuticular resistance R sto Stomatal resistance

Global Tropospheric Ozone Budget Global Model Budgets Observational Constraints Tropospheric O 3 burden 340±40 Tg335±10 Tg Strat-trop exchange 550±170 Tg/yr550±140 Tg/yr Photochemistry 450±300 Tg/yr?? Deposition 1000±200 Tg/yr?? Photochemistry Strat.-Trop. Exchange Deposition Ozone impacts: vegetation damage, stomatal closure, reduced CO 2 and H 2 O fluxes, near-surface oxidation, …

SOx NHx mg(S)/m 2 /yr mg(N)/m 2 /yr Accent Studies GBC, 2006

Aims Traceability across models from box models up to ESM – Include latest obs-based developments in deposition schemes – Ensure new advances can be rapidly implemented across all models Develop metrics to assess representation of dry deposition – Provide clear, cross-scale benchmarks for characterising deposition – Provide rigorous comparison against observations at small scales – Define constraints for modelling land/atmos interactions in ESM Self-consistency across gas phase and aerosol species – Aim for integrated, unified approach where possible Forge stronger links with land-surface researchers – e.g., interface with JULES model, etc. Not trying to reinvent deposition here: focus on unifying current schemes and ensuring coherence and consistency, not on developing new schemes!

Climate Impacts and Future Air Quality Importance of including Earth System interactions when looking at future atmos composition (JGR, 2010)

Current Plans Catherine Hardacre to start 1 st Feb 2013 Characterize schemes currently in use in UK models – Focus on approaches in UKCA and DO3SE – Identify necessary development pathway – Coordinate with other efforts under JULES, ECLAIRE, UKCA… Provide improved framework for observational comparison – Work with observations to define key ecosystem-scale tests – Initial focus O 3 but need to work across species (NO y, NH 3, SO 2, aerosol…) Define range of metrics for comparing schemes – Global and regional diagnostics for budgets – Characterise impacts on vegetation as well as atmospheric composition – Quantify sensitivity to vegetation type, phenology, leaf area, soil, PBL met, etc. to characterise spatial and temporal variability and assoc. uncertainty – Apply metrics to model intercomparison data (HTAP, ACCMIP, CCMI) and encourage use in future studies

Practical Aspects Gain insight from involvement in international model studies – Upcoming process-focussed CCMI and HTAP intercomparisons Contribution to UK ESM efforts – New interactions with land surface community, etc. – Provide opportunities for new science, e.g., Earth System interactions – Benefits for air quality/ecosystem impact studies, too. Welcome input from all in ACITES and ESM communities – What do you need? How can we be of most use? – Which processes/species are most important to look at?

Objectives – To extend Weseley deposition scheme based on experience with DO3SE model (in UKCA, CTM, box model) – To characterise current schemes based on their impacts on atmos composition and on vegetation (metric design) – To provide improved framework for observational comparison – To explore impacts of vegetation heterogeneity: sensitivity to vegetation type, phenology, leaf area, PBL met. Wider benefits – Gain insight from involvement in ongoing international model intercomparisons, e.g., ACCMIP – Provide input to future air-quality assessments, e.g., under HTAP – Involve UK land surface community/JULES DO3SE model (Lisa Emberson, SEI)