Quantifying Air Quality Impacts on Sensitive Habitats
Dr Ben Marner
Outline
• Typical Pollutants of Concern• Assessment Criteria• Background Data Sources • Quantifying Local Components• Assessment Outcomes
• 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
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
Assessment Criteria
Pollutant Averaging Period
Value (g/m3)
NOx
annual mean 30
24-hour mean 75
NH3 annual mean 1 – 3
SO2 annual and winter means
10 - 30
Pollutant Typical RangeNutrient Nitrogen 5 – 30 kg/ha/yr
Acid Nitrogen and Sulphur
Site-specific function
Critical Levels
Critical Loads
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
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)
Background vs Near-source
Just using “background” data (and not treating local sources explicitly) significantly underestimates impacts near to those sources
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* Outdated (Most air quality consultants stopped using the DMRB model nearly 10 yrs ago)
Modelling Deposition
F = Vd x C
F = deposition fluxC = 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
Usually Omitted from Deposition Calculations
• Diurnal and seasonal variations• Spatial variations in deposition velocity• Individual surface resistances• Bi-directional flux• Co-deposition• Edge effects
Outcomes
A) No critical levels or critical loads are exceeded: No significant effects
B) 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.
Outcomes
SPA
Head Office 23 Coldharbour Road, Bristol BS6 7JTTel: 0117 974 1086
London Office12 Airedale Road, London SW12 8SFTel/Fax: 020 8673 4313
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