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* Outdated (Most air quality consultants stopped using the DMRB model nearly 10 yrs ago)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

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