This document discusses quantifying air quality impacts on sensitive habitats. It outlines typical pollutants of concern like NOx, NH3, and SO2 and assessment criteria including critical levels and critical loads. It describes background data sources for pollutant concentrations and fluxes. It explains that near-source impacts are underestimated if only using background data and that monitoring and modeling are needed. It provides example values for deposition velocities and notes factors usually omitted from deposition calculations. Finally, it outlines three potential outcomes for assessments: no significant effects, potential effects cannot be discounted, or impacts are less than 1% of critical level/load (no significant effects).

1. Quantifying Air Quality
Impacts on Sensitive Habitats
Dr Ben Marner

2. Outline
• Typical Pollutants of Concern
• Assessment Criteria
• Background Data Sources
• Quantifying Local Components
• Assessment Outcomes

3. • Ambient Concentrations
 NOx
 NH3
 SO2
 HF
• Deposition Fluxes
 Total nitrogen (eutrophication)
All reactive nitrogen species as gases, particles
and in water
 Acid deposition (acidification)
All reactive nitrogen and sulphur as gases,
particles and in water
Typical Pollutants

4. Assessment Criteria 1
• Critical Levels
“concentrations of pollutants in the atmosphere above which
direct* adverse effects … may occur….
*refers to the impact of pollutants directly, such as occurs with SO2 and plant leaves,
rather than indirectly via the sulphur pathway through soils”.
• Critical Loads
“… an exposure#
to one or more pollutants below which
significant harmful effects …do not occur …”
#
means deposition experienced on an area basis e.g. eq m-2
yr-1
; kg ha-1
yr-1
”.
1
www.unece.org/env/lrtap/WorkingGroups/wge/definitions.html

5. Assessment Criteria
Pollutant Averaging
Period
Value
(µg/m3
)
NOx annual mean 30
24-hour mean 75
NH3 annual mean 1 – 3
SO2 annual and
winter means
10 - 30
Pollutant Typical Range
Nutrient Nitrogen 5 – 30 kg/ha/yr
Acid Nitrogen and
Sulphur
Site-specific
function
Critical Levels
Critical Loads

6. When Assessments Required
• Environment Agency
 SACs SPAs etc. 10-15 km
 SSSIs, NNRs, LNRs etc.
2km
• DMRB Manual
 200m from affected road
• Local Planning Authorities
 Some have own criteria

7. Background Sources
 Site-specific measurements
 www.apis.ac.uk
(5 x 5 km and 3-yr average concentrations and fluxes)
 pollutantdeposition.defra.gov.uk/data
(5 x 5 km average year-specific and source-apportioned
concentrations and fluxes)
 laqm.defra.gov.uk/review-and-
assessment/tools/background-maps.html
(1 x 1 km year-specific concentrations with future projections)

8. Background vs Near-source
Just using “background” data (and
not treating local sources explicitly)
significantly underestimates
impacts near to those sources

9. Quantifying Near-source
Components
• Monitoring
• Modelling
 ADMS
 Aermod
 Caline
 (DMRB Model*)
 Verification, verification, verification
* Outdated (Most air quality consultants stopped using the DMRB model nearly 10 yrs ago)

10. Modelling Deposition
F = Vd x C
F = deposition flux
C = ambient concentration
Vd = deposition velocity
Reference Vd NO2 (cm/s)
Range in obvious literature 1
0.0002 – 0.6
DMRB Manual 2
0.1
AQTAG 3
0.15 - 0.3
1
Marner and Harrison, 2004. A spatially refined monitoring based study of atmospheric nitrogen deposition. Atmospheric Environment V38, I30 P 5045-5056
2
http://www.standardsforhighways.co.uk/dmrb/vol11/section3/ha20707.pdf
3
Air Quality Technical Advisory Group - Technical guidance on detailed modelling approach for an appropriate assessment for emissions to air (19/10/11)
Example Values of Vd NO2 from Literature
Vd

11. Usually Omitted from
Deposition Calculations
• Diurnal and seasonal variations
• Spatial variations in deposition velocity
• Individual surface resistances
• Bi-directional flux
• Co-deposition
• Edge effects

12. Outcomes
A) No critical levels or critical loads are exceeded:
 No significant effects
A) Scheme (in isolation and combination) impacts
<1%* (or <10%) of critical level or critical load:
 No significant effects
C) If neither A nor B is true:
 The potential for significant effects cannot be discounted
by the air quality specialist
* The EA allows much bigger increases if the emission is from
intensive farming or to certain ‘non-sensitive’ sites.

13. Outcomes
SPA

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