Modelling the deposition of pollutants on habitats involves quantifying the deposition of sulfur and nitrogen compounds in the UK using concentration-based estimates. Measurements of pollutant concentrations are combined with meteorological data and land use information to calculate dry deposition fluxes and wet deposition. This allows mapping of deposition fields and exceedances of critical loads for acidity and eutrophication on habitats. While sulfur deposition was historically the main driver of acidification, nitrogen deposition currently exceeds critical loads over much of the UK, and reductions in deposition have been smaller than expected based on emissions inventories. This suggests emissions reductions may be overestimated or atmospheric chemistry changes are larger than anticipated.

1. Modelling the deposition of pollutants on
habitats
David Fowler FRS
DMUG 19th April 2018

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. Issues
• Acid deposition
• Eutrophication due to nitrogen deposition

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. 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. 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. CANOPY
CIS
ATMOSPHERE
SOIL
Plant
physiology
Molecular
diffusion
Turbulent
exchange
Surface
chemistry
Soil
chemistry
Soil biology
and physics
Dry deposition
MORECS
Meteorology

8. The resistance analogy

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. SO2 deposition to grassland

11. NO2 deposition on vegetation

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. 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. 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. Bi-directional exchange

16. Canopy compensation point

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. 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. 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. Orographic Cloud formation and the size and concentrations of
particles


21. Cloud droplet deposition

22. Orographic enhancement of wet deposition

23. Orographic Cloud formation and the size and concentrations of
particles


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. Orographic Cloud
5.6 – 5.85
Height Above Sea Level (m)
Rain
Concentrations of major ions in rain and orographic cloud

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. 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. NAMN/AGANet: Current status (2016)
X
Polloch
X
Polloch
DELTA 53 (30 = AGANet)
ALPHA 41
Both 9
TOTAL 85

29. 2 UK supersites - Auchencorth and Chilbolton
Auchencorth Moss
http://pollutantdeposition.defra.gov.uk/emep
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

31. SO2

32. NO2

33. NH3

34. Deposition maps (Wet N + dry dep HNO3,NO2,NO3,cloud N)
Wet N dep Dry dep HNO3
Dry dep NO2 Total NOy dep

35. Total Nitrogen deposition
in the UK

36. 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
http://pollutantdeposition.defra.gov.uk/
http://uk-air.defra.gov.uk
http://www.ceh.ac.uk/sci_programmes/UKEAP-Project.html
http://cldm.defra.gov.uk/index.htm
http://uk-air.defra.gov.uk/research/air-quality-modelling
Submitted to databases
EMEP
OSPAR
UK-Air
UK Pollutant Deposition Air pollution information service
APIS
National Assessments of the
UK environment (e.g. RoTAP)
http://www.apis.ac.uk/
http://www..scail.ceh.ac.uk/

37. 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

38. 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

39. CBED FRAME and EMEP4UK compared

40. CBED FRAME EMEP4UK compared 2010-2012

41. UK deposition changes with tijme

42. NOx Emissions &
Total NOx Deposition (wet & dry NO2+ HNO3 & aerosol)

43. 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%

44. 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

45. NH3 Emissions & Total NHx Deposition (wet + dry + aerosols*)
*estimated as 0.05 of wet & dry from 1997 to 1999

46. UK NH3 Emissions and Ambient Concentrations
Emission inventory -22% over 15 years

47. 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

48. 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

49. • Questions?

50. DEALING WITH SPATIAL SCALE
European exceedances
of the critical load
for nitrogen
National targets
and policy

51. Day

52. 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

53. 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

56. • 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.

57. • Increase in regional oxidation NOx to NOy
• Uncertainty in emissions including the
effect
Causes of changes in NOy budget

58. 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

59. 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