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Modelling the Deposition of Pollutants on Habitats


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David Fowler, Centre for Ecology and Hydrology

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Modelling the Deposition of Pollutants on Habitats

  1. 1. Modelling the deposition of pollutants on habitats David Fowler FRS DMUG 19th April 2018
  2. 2. Outline • A little history • Principles….the objectives of the model and the approach • Dry deposition of S and N compounds • Wet and cloud deposition • The measured concentration fields • Mapped deposition fields and budgets • Comparisons with FRAME and EMEP4UK • Trends
  3. 3. Issues • Acid deposition • Eutrophication due to nitrogen deposition
  4. 4. Requirements • We needed to quantify deposition (S and N) to the UK….budgets mass balance and fate of emissions • Exceedance of Critical Loads for acidity, nutrient nitrogen and ozone • Habitat specific deposition
  5. 5. Policy drivers UNECE Gothenburg Protocol: 1999, revised 2012 ➢protocol to reduce acidification, eutrophication and ground-level ozone ➢ 1999: 2010 Emission ceilings set for NH3, SO2, NOx, O3. ➢ 2012: 2005-2020 emission cuts agreed: NH3: 6% SO2: 59% NOx: 42% VOCs: 28% PM: 22%. National Emissions Ceilings Directive 2001/81/EC (NECD) ➢This requires pig and poultry farms (above stated size thresholds) to reduce emissions using Best Available Techniques. ➢ 2001: National emission ceilings set for NH3, SO2, NOx, VOCs. ➢ Areas with critical loads of acid depositions reduced by >50% c.f. 1990. ➢ Under revision. EU Integrated Pollution Prevention and Control Directive (IPPC) 2008/1/EC
  6. 6. CBED Concentration based estimates of deposition • Principles • To calculate deposition to the UK landscape using measured concentrations of pollutants • In this way the estimates are independent of the emission inventories • Meteorological data: measured UK (MORECS, CHESS) 30y, mean providing hourly average St, U, T, rh, ppt, • Land use at 1 km from CIS (countryside survey information) • Resolution 5km x 5km, hourly fluxes of gases and particulate matter, monthly wet deposition.
  7. 7. CANOPY CIS ATMOSPHERE SOIL Plant physiology Molecular diffusion Turbulent exchange Surface chemistry Soil chemistry Soil biology and physics Dry deposition MORECS Meteorology
  8. 8. The resistance analogy
  9. 9. CBED Concentration based estimates of deposition • Principles • 5 Land use classes: arable, grassland, moorland, forest, urban • Land use and time determines roughness length for atmospheric resistances (ra and rb) • For SO2, NO2 , HNO3 deposition only • For NH3 a compensation point approach
  10. 10. SO2 deposition to grassland
  11. 11. NO2 deposition on vegetation
  12. 12. Auchencorth Moss (AU) & Sutton Bonnington (SB) Edinburgh AU SB Nottingham Auchencorth Moss 55o 47’ 30’’ N, 3o 14’ 20’’ W Altitude 270 m a.s.l Ombrotrophic mire, > 1000 ha Sutton Bonnington 52o 50’ 24’’ N, 1o 15’ E Altitude 45 m a.s.l Arable farmland, > 4 ha
  13. 13. KhsKha KhhonoKhc Kn1 Ks1Kc1Ka NH3,aq CO2,aq HNO2,aq NH3 CO2 HNO2 SO2 SO2,aq CO3 2- SO3 2- SO4 2- NH4 + HCO3 - NO2 - HSO3 - HSO4 - Ks2Kc2 Ks3 Kw H2O H+ +OH- d Rd AQUEOUS GASEOUS Kha s(NH3) Rs Rcut Fcut Rb Ra{z-d} {z-d} {z0’}=c {z0} WET DRY HNO3 HCl Cl- NO3 - H2O2 O3 APOPLAST Ft Fd Fs K+ Mg2+ Na+ Ca2 + K+ Mg2+ Na+ Ca2 + Ka NH3,aqNH4 + Kw H2O H+ +OH- The surface reactions are regulated by chemistry (and esp SO2/NH3) interactions in suface water films
  14. 14. WHEAT 0 20 40 60 80 100 120 140 1996 1997 1999 2001 2003 May-JulAverageRc,sm-1 Canopy resistance to SO2 deposition changes with time
  15. 15. Bi-directional exchange
  16. 16. Canopy compensation point
  17. 17. CBED Concentration based estimates of deposition • Calculate atmospheric and surface resistance components • Combine with measured concentrations to provide: • Fluxes of SO2, NO2, HNO3, NH3, • Particulate matter and cloud water deposition (only significant above 600m asl) • Wet deposition and corrections for orographic enhancement of wet deposition due to seeder – feeder precipitation scavenging
  18. 18. Particlediameterdp[m] 0.0010.010.1 1 10100 DepositionvelocityVd[mms-1] 0.1 1 10 100 ASASP-x12-27/05/99 (u*=0.36ms-1 ) ASASP-x13-29/10/99 (u*=0.31ms-1 ) ASASP-555x02-21/06/99 (u*=0.32ms-1 ) Slinnmodel Vd = - flux / concentration [m s-1] = [# m-2 s-1] / [# m-3] Aerosol deposition velocities as a function of size to moorland Aerosol deposition velocities as a function of size to moorland
  19. 19. Orography and deposition processes • Lifting particulate matter cools them leading to droplet formation and with further cooling the droplets grow • Particle deposition increases rapidly with particle size • Vegetation in the uplands collect droplets and particles efficiently
  20. 20. Orographic Cloud formation and the size and concentrations of particles 
  21. 21. Cloud droplet deposition
  22. 22. Orographic enhancement of wet deposition
  23. 23. Orographic Cloud formation and the size and concentrations of particles 
  24. 24. OROGRAPHIC (FEEDER) CLOUD AIR FLOW aerosols activated into cloud droplets at cloud base scavenging of feeder cloud hill profile more deposition in seeder-feeder rain fall SEEDER CLOUD
  25. 25. Orographic Cloud 5.6 – 5.85 Height Above Sea Level (m) Rain Concentrations of major ions in rain and orographic cloud
  26. 26. • Data from Precip-Net provides input for: – EMEP and OSPAR1 reporting – Modelling and mapping pollution concentration & wet deposition – Critical loads exceedance mapping – Assessment of compliance with Habitats Directive • 39 fortnightly bulk rain sites • 2 daily wet only collectors (DWOC) – Auchencorth Moss – Chilbolton Data reported to EMEP Precip-Net 1 Convention for the Protection of the Marine Environment of the North-East Atlantic
  27. 27. UKEAP: Component networks NAMN 85 sites AGANet 30 sites Precip-Net 39 sites NAMN AGANet Precip-Net NO2-Net Method DELTA / ALPHA DELTA Bulk rain collector Diffusion Tubes Resolution Monthly Monthly 2-weekly (daily at 2 sites) 4-weekly Species NH3 NH4 + HNO3, SO2, HCl, NO3 -, SO4 2-, Cl-, Na+, Ca2+, Mg2+ pH, conductivity, NH4 +, NO3 -, PO4 3-, SO4 2-, Cl-, Na+, K+, Ca2+, Mg2+ NO2 Inception 1996 1999 1985 1984 NO2-Net 24 sites ALPHA
  28. 28. NAMN/AGANet: Current status (2016) X Polloch X Polloch DELTA 53 (30 = AGANet) ALPHA 41 Both 9 TOTAL 85
  29. 29. 2 UK supersites - Auchencorth and Chilbolton Auchencorth Moss Measurement Method Water-soluble gases + particles at PM2.5 & PM10 MARGA Black carbon PM2.5 Aethalometer NO/NO2 Photolytic converter Meteorology (wind speed, dir’n., temp., RH, precip’n) Automated met station Ozone UV photometer PM2.5 and PM10 mass (daily) Filter (gravimetric) PM2.5 and PM10 mass (hourly) TEOM/FDMS PAH (vapour and particle) Digitel hi-vol PAH (precipitation) Bulk sampler TOMPS (air) Hi-vol Hydrocarbons (C2 – C8) Online GC-FID Particle size and number SMPS Mercury (elemental) in air CVAF Mercury (speciated) in air CVAF Mercury (precipitation) CVAF Heavy metals PM10 (air) ICP-MS Heavy metals (precip’n) ICP-MS Ozone, NOx, SO2 fluxes Automated analyzers Trace gas fluxes CoTAG ECOC (weekly) Filter
  30. 30. SO2
  31. 31. NO2
  32. 32. NH3
  33. 33. Deposition maps (Wet N + dry dep HNO3,NO2,NO3,cloud N) Wet N dep Dry dep HNO3 Dry dep NO2 Total NOy dep
  34. 34. Total Nitrogen deposition in the UK
  35. 35. UKEAP monitoring measurements Modelling and mapping pollutant concentrations and deposition Critical Loads and exceedence mapping Local Environmental Impact Assessments Screening tools e.g. SCAIL Public access to data Measurement data uses Submitted to databases EMEP OSPAR UK-Air UK Pollutant Deposition Air pollution information service APIS National Assessments of the UK environment (e.g. RoTAP)
  36. 36. UK deposition network changes • 1986 wet deposition network established • 1996 NO2 (diffusion tube) measured • 1997 NH3 alpha samplers, (2000 delta denuder) • 2000 HNO3 SO2 HCl denuder • 2000 aerosol SO4 ,NO3, NH4
  37. 37. Key reference Smith, R I., Fowler, D., Sutton, M.A., Flechard, and Coyle, M. 2000. Regional estimation of pollutant gas dry deposition in the UK: model description, sensitivity analyses and outputs. Atmospheric Environment 34, 3757-3777 RoTAP2012 Review of Transboundary Air Pollution
  38. 38. CBED FRAME and EMEP4UK compared
  39. 39. CBED FRAME EMEP4UK compared 2010-2012
  40. 40. UK deposition changes with tijme
  41. 41. NOx Emissions & Total NOx Deposition (wet & dry NO2+ HNO3 & aerosol)
  42. 42. EMISSIONS DRY DEPOSITION WET + CLOUD DEPOSITION 60 100 680 INPUT EXPORT 580 60 From non- UK/Europe EMISSIONS DRY DEPOSITION WET + CLOUD DEPOSITION 40 80 300 INPUT EXPORT 210 30 From non- UK/Europe EMISSION 680 kT N DEPOSITION 160 kT N 23% deposited in UK EMISSION 300 kT N DEPOSITION 120 kT N 40% deposited in UK 1999-2001 2011-2013 Changes in the mass budget for oxidized N over the UK 2000 to 2013 -55% -25%
  43. 43. Total UK reduced N deposition 2013 • No trend in wet NH4 Deposition 0ver 30 years • No trend in total reduced N deposition • Small changes in spatial deposition
  44. 44. NH3 Emissions & Total NHx Deposition (wet + dry + aerosols*) *estimated as 0.05 of wet & dry from 1997 to 1999
  45. 45. UK NH3 Emissions and Ambient Concentrations Emission inventory -22% over 15 years
  46. 46. Summary • UKEAP measurements quantify the exposure of ecosystems and underpin the assessment of effects for acidification and eutrophication in the UK • The measured concentration and deposition fields independently monitor the effects of control measures • S deposition was the main driver of the acidifying input for sensitive catchments and to critical load exceedance and has been most important historically; but has declined sufficiently for ecosystems to recover • N deposition in the UK exceeds critical loads for sensitive ecosystems over ~70% of the country
  47. 47. Summary • Eutrophication by Nitrogen compounds remains a major problem and the small reduction in deposition to date is insufficient to allow recovery to begin • Measured N deposition data suggest that emission reductions (NAEI) for both oxidized and reduced nitrogen have been overestimated
  48. 48. • Questions?
  49. 49. DEALING WITH SPATIAL SCALE European exceedances of the critical load for nitrogen National targets and policy
  50. 50. Day
  51. 51. Measurements : UK Networks National Acid gas, and Aerosol Network (AGAnet) 30 sites Ammonia network (85 sites) Rain chemistry network (Precip-Net) NH3 SO2 NO2 N depositionHNO3 N Deposition
  52. 52. NO2-NET • NAEI emissions decreasing • Greatest deceases seen at southern sites more influenced by traffic/industry • Very rural sites don’t all appear be influenced by the emission reductions
  53. 53. • Oxidized N changes with time • Much smaller decline in concentration and deposition than expected • Significant changes in atmospheric chemistry • Conclusion: reductions in emissions are smaller than official emission statistics, Or that atmospheric chemistry changes are large.
  54. 54. • Increase in regional oxidation NOx to NOy • Uncertainty in emissions including the effect Causes of changes in NOy budget
  55. 55. Checking emission inventories • London emission inventory (from NAEI) accounted for half of measured NOx emission in an aircraft study of N emissions in London. • Oxidized N is present in many different compounds, only a few of which are measured widely • Atmospheric chemistry of N is more complex than S • There does not appear to be sufficient effort validating emissions
  56. 56. Measurements : UK Networks National Acid gas, and Aerosol Network (AGAnet) 30 sites Ammonia network (85 sites) Rain chemistry network (Precip-Net) NH3 SO2 NO2 N depositionHNO3 N Deposition