IAQM Meeting 1

Thoughts from Atkins

IAQM Guidance for Planning

15 July 2016

IAQM Meeting 2

Impact Magnitude Descriptors

Depending on when rounding applied• Descriptor can change depending on:

– Modelled results rounded to 1, 2 or more decimal places? – Percent change rounded up to whole number

15 July 2016

Some inconsistencies can rise

IAQM Meeting 3

Differences with HE IAN

• HE IAN does not consider below AQAL as potentially significant• Requires reporting of scheme results to 1 d.p.• Imperceptible change is defined as ≤ 1% of AQAL (≤ 0.4 µg/m3) .

15 July 2016

Potential for challenge on scheme assessments

DM DS Change (DS-DM)

% change relative to

AQAL

Increase or Decrease?

Long-term average

conc (max)

Long-term average as % of AQAL

Impact from IAQM

guidance

HE IAN 174/13

31.04582 36.5064 5.4606 14 increase 36.5 91 Moderate -

31.05 36.51 5.46 14 increase 36.5 91 Moderate -

31 36.5 5.5 14 increase 36.5 91 Moderate N/A

42.1234 42.3554 0.2320 1 increase 42.4 106 Moderate -

42.12 42.36 0.23 1 increase 42.4 106 Moderate -

42.1 42.4 0.3 1 increase 42.4 106 Moderate Imperceptible

42.1234 42.4534 0.3300 1 increase 42.5 106 Moderate -

42.12 42.45 0.33 1 increase 42.5 106 Moderate -

42.1 42.5 0.4 1 increase 42.5 106 Moderate Small

IAQM Meeting 4

Indicative assessment criteria

Criteria for change in LDV traffic• Can result in an unmanageably wide network:

– Traffic models often do not extend far for small developments

– Is there evidence NO2 from 100 AADT LDVs > 0.2 µg/m3

Criteria for change in construction traffic• No guidance for how long construction traffic change needs to be

in place to require assessment– Previous guidance said a year or more; – Now left to professional judgement

15 July 2016

Affected road network can be very large

IAQM Meeting 5

Suggestions

15 July 2016

Guidance to define when to apply rounding.to avoid consistencies in results from different parties:• 1 decimal place would be

– Measurable– Appropriate level of detail from

modelling– Consistent with HE guidance

Consider whether AADT criteria can be changedto avoid unnecessarily large modelled road networks with many negligible results.• 500 AADT LDVs in AQMA• 1000 elsewhere?