Thoughts from Atkins IAQM Guidance for Planning 15 July 2016 1 IAQM Meeting
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?