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Alison Redington* and Derrick Ryall* Dick Derwent** * Met Office, Exeter, United Kingdom

MODELLING PARTICULATE SULPHATE AND NITRATE IN NORTH WEST EUROPE WITH A LAGRANGIAN DISPERSION MODEL. Alison Redington* and Derrick Ryall* Dick Derwent** * Met Office, Exeter, United Kingdom ** rdscientific, Newbury, United Kingdom EMEP Workshop on PM Measurement and Modelling

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Alison Redington* and Derrick Ryall* Dick Derwent** * Met Office, Exeter, United Kingdom

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  1. MODELLING PARTICULATE SULPHATE AND NITRATE IN NORTH WEST EUROPE WITH A LAGRANGIAN DISPERSION MODEL Alison Redington* and Derrick Ryall* Dick Derwent** * Met Office, Exeter, United Kingdom ** rdscientific, Newbury, United Kingdom EMEP Workshop on PM Measurement and Modelling New Orleans, April 2004

  2. PM10 TRENDS IN THE UNITED KINGDOM IN URBAN CENTRES

  3. UK POLICY-MAKERS CONCERNS • What are the levels, sources and characteristics of PM10 and PM2.5 in the UK ? • What are the trends in PM10 and PM2.5 ? • What are the extent of exceedances of air quality targets currently and in the future ? Some form of modelling is required to answer these questions.

  4. MODELLING SUSPENDED PARTICULATES IN THE UNITED K INGDOM • Primary vs secondary and inorganic vs organic particulate matter • Particulate sulphate and nitrate is main focus of this study • Role of long range transboundary transport and local formation • Application of the UK Met Office NAME Lagrangian dispersion model • Aim is to give source attribution to particulate sulphate and nitrate at 15 minutes time resolution and 15 km spatial resolution

  5. NAME MODEL • UK Met Office’s operational dispersion model (1-1000’s kms) • Lagrangian - pollutant modelled by large numbers of ‘parcels’ released into the ‘model’ atmosphere • Model driven by meteorological fields from the Met Office’s operational forecast model • Particles are transported by local mean wind in 3-dimensions • Diffusion by turbulence is represented by random walk techniques, displacing particles in both the horizontal and vertical

  6. LAGRANGIAN DISPERSION MODEL Receptor Source 65°N 20°E emissions grid 15°W 43°N Long-range transport and dispersion of an inert tracer

  7. max O3 125 ppb 11/08/03

  8. FORMATION OF SECONDARY INORGANIC AEROSOLS SO2 + OH = HOSO2 HOSO2 + O2 = HO2 + SO3 SO3 + H2O = H2SO4 = sulphate aerosol SO2aq + H2O2 = H2SO4 = sulphate aerosol SO2aq + O3 = H2SO4 = sulphate aerosol NO2 + OH = HNO3 = nitrate aerosol NO2 + O3 = NO3 + O2 NO2 + NO3 = N2O5 = nitrate aerosol NH3aq + HNO3aq = NH4NO3aq = nitrate aerosol

  9. OPERATIONS IN A LAGRANGIAN DISPERSION MODEL • Emit some new air parcels, each loaded up with SO2 and NOx • Move air parcels to new locations with 3-d turbulent wind fields • Locate air parcels in Eulerian grid • Calculate air concentrations in Eulerian grid • Allow for chemical transformations and deposition • Recalculate air parcel masses This is the main time-stepping algorithm in a source-oriented Lagrangian dispersion model.

  10. ANNUAL AVERAGE SO2 CONCENTRATIONS - 1996 Compares well with EMEP observations for 1996

  11. ANNUAL AVERAGE PARTICULATE SULPHATE CONCENTRATIONS - 1996 Compares well with observations for 1996

  12. ANNUAL AVERAGE NO2 CONCENTRATIONS - 1996 Compares well with rural observations for 1996

  13. ANNUAL AVERAGE HNO3 CONCENTRATIONS - 1996 No observations for direct comparison

  14. ANNAUL AVERAGE PARTICULATE NITRATE CONCENTRATIONS - 1996 No observations for direct comparison

  15. ANNUAL AVERAGE SECONDARY INORGANIC AEROSOL - 1996 Tendency to overestimate rural PM10 observations

  16. EMEP MONITORING SITE NETWORK

  17. STATISTICS FOR EVALUATION OF DAILY MEASURED AND MODELLED PARTICULATE SULPHATE FOR 1996 agreement is somewhat disappointing, over-prediction during wintertime, lack of background sulphate from North Atlantic

  18. STATISTICS FOR EVALUATION OF MONTHLY MEASURED AND MODELLED HNO3 AND NO3 FOR 1999-2000 nitrate aerosol is slightly over-predicted, nitric acid is under-predicted and shows poorer performance, however the data are inadequate

  19. EMEP MONITORING SITE NETWORK

  20. WINTERTIME AND SUMMERTIME MODEL PERFORMANCE timing of peaks is excellent, but overestimation during winter

  21. SOURCE ATTRIBUTION • Each air parcel emitted into the NAME model keeps a record of the location where it was emitted • It is straightforward to construct a map showing the origins of the particulate sulphate and nitrate found at any location in the model • The source allocation given for secondary pollutants refers to the origins of the primary pollutant precursors

  22. MEAN DIURNAL VARIATIONS IN PARTICULATE NITRATE DURING 10 DAYS IN MAY 2003 AT A RURAL EMEP SITE AT HARWELL OXFORDSHIRE UK Preliminary data kindly provided by Steve Moorcroft, Casella Stanger

  23. CONCLUSIONS • Model development is severely hampered by lack of good observations of the individual components of PM10 and PM2.5 • These need to be of hourly time resolution and co-located with other air quality measurements • Artefact-free nitrate observations are particularly sparse in Europe and must distinguish ammonium nitrate from sodium and calcium nitrates • Cloud liquid water content, low cloud amount, precipitation amounts and boundary layer depths are difficult quantities to obtain from meteorological models with sufficient accuracy for secondary particle modelling

  24. ACKNOWLEDGEMENTS • To the United Kingdom Department for Environment Food and Rural Affairs for their support through contract CPEA 7 • To Alison Redington and Derrick Ryall United Kingdom Met Office for their patient work with the NAME model • To Steve Moorcroft, Casella Stanger for contributing his preliminary continuous observations of particulate nitrate • To members of the United Kingdom Air Quality Expert Group for their helpful discussions • To Environment Canada for their generous offer of help with travel costs

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