Discussion meeting: Mitigating operational impacts

1. rpsgroup.com
MITIGATION OF
DEVELOPMENT AIR
QUALITY IMPACTS –
THE IAQM’S POSITION
Fiona Prismall
March 2019

2. What are Position Statements?
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“The IAQM issues Position Statements on matters that could affect the way in which Members carry out
their professional tasks and on air quality topics and issues where the IAQM can provide a unique
perspective from which to give a professional opinion.”
There are currently five Position Statements publicly available on the IAQM website:
• Dealing with Uncertainty in Vehicle NOx Emissions Within Air Quality Assessments
• Mitigation of Development Air Quality Impacts
• Competent Air Quality Expert for Environmental Impact Assessment
• Assessment of Air Quality Impacts from Combustion Plant with Limited-hours of Operation
• Use of a Criterion for the Determination of an Insignificant Effect of Air Quality Impacts on Sensitive
Habitats

3. 3

4. How are Position Statements Developed?
4
Position Statements are:
• Drafted by members of the Committee or members of the IAQM to whom the chair has delegated this
task.
• The first draft is reviewed by the Committee with a view to reaching a consensus agreement on the
Interim Position Statement.
• The Interim Position Statement is published on the IAQM website to allow Members the opportunity
to comment.
• At the Committee meeting following the publication of the Interim Position Statement on the IAQM
website, any comments received are discussed and amendments agreed.
• The final Position Statement is then published on the website.

5. Mitigation of Development Air Quality Impacts Position Statement
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• The first Position Statement “Mitigation of Development Air Quality Impacts” was
published in 2015 and subsequently updated in June 2018.
• Members predict pollution concentrations from/at individual new developments in their
Air Quality Assessments. These numbers are compared with AQS objectives or limit
values to inform their professional judgement on the effects.
• In those situations where the adverse effect is considered to be significant, mitigation
usually needs to be applied.
• For point sources, we often have good evidence/data on the abatement efficiency of
proposed emissions controls, allowing us to be reasonably certain in our prediction of
the residual impact after implementation of the mitigation for the individual
development.
• For non-point sources, there is much less quantitative evidence on the efficacy of the
various mitigation options available. This makes it more difficult to confidently
recommend a mitigation solution for a new development that would sufficiently reduce
concentrations at the point of receptor exposure.
• But… we still need to arrive at a conclusion on the residual impact in their Air Quality
Assessment.

6. Mitigation of Development Air Quality Impacts Position Statement
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This raises a number of questions for IAQM Members assessing the operational impacts of individual
general development schemes (e.g. residential, commercial, retail, etc), where distributed sources such
as road traffic are often the main issue:
• How do we weigh up the likely efficacies of different mitigation solutions in removing the “excess
impact”, when there are few robust data sources available to allow a comparison on a like-for-like
basis?
• Where there are several alternative mitigation/control options, how should we choose?
• Should some mitigation approaches be used in preference to others, or are all born equal?
• Should all possible mitigation options be applied, or just a selection; and if the latter, on what basis
do we choose the right mix?
• What is and is not within the developer’s power to influence?
• And how far should a developer reasonably be expected to go?

7. What does Central Government tell us to do?
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• The National Planning Policy Framework gives no specific detail on air quality mitigation for general
development purposes
• The national Planning Practice Guidance states that:
“Mitigation options where necessary will be locationally specific, will depend on the proposed
development and should be proportionate to the likely impact. It is important therefore that local
planning authorities work with applicants to consider appropriate mitigation so as to ensure the new
development is appropriate for its location and unacceptable risks are prevented. Planning
conditions and obligations can be used to secure mitigation where the relevant tests are met.”
It continues by listing some examples of mitigation;
• “the design and layout of development to increase separation distances from sources of air pollution;
• using green infrastructure, in particular trees, to absorb dust and other pollutants;
• means of ventilation;
• promoting infrastructure to promote modes of transport with low impact on air quality;
• controlling dust and emissions from construction, operation and demolition; and
• contributing funding to measures, including those identified in air quality action plans and low
emission strategies, designed to offset the impact on air quality arising from new development.”

8. What is the IAQM’s Position on this Issue?
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The NPPG provides no guidance on how the most appropriate mitigation option(s) should be chosen for
a given application, or on the efficacy of the different mitigation options.
• The IAQM position is that the appropriate mitigation solution for the operational air quality impact of
any given individual general development scheme should be principle-led rather than specified by
detailed prescription.
• The IAQM recommends some basic hierarchy principles for mitigating the operational air quality
impacts.
• This hierarchy is suitable both for impacts caused by a potentially polluting new development, and for
the impact of exposure of new occupants of a development proposed in an area of existing poor air
quality.

9. The Heirarchy
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• Preference should be given to preventing or avoiding exposure/impacts to the pollutant in the first
place by eliminating or isolating potential sources or by replacing sources or activities with
alternatives. This is usually best achieved through taking air quality considerations into account at the
development scheme design stage.
• Reduction and minimisation of exposure/impacts should next be considered, once all options for
prevention/avoidance have been implemented so far as is reasonably practicable (both technically
and economically). To achieve this reduction/minimisation, preference should be given first to:
• mitigation measures that act on the source; before
• mitigation measures that act on the pathway; which in turn should take preference over
• mitigation measures at or close to the point of receptor exposure all subject to the efficacy, cost
and practicability of the available solutions.
• Off-setting a new development's air quality impact by proportionately contributing to air quality
improvements elsewhere (including those identified in air quality action plans and low emission
strategies) should only be considered once the solutions for preventing/avoiding, and then for
reducing/minimising, the development-specific impacts have been exhausted. Even then, offsetting
should be limited to measures that are likely to have a beneficial impact on air quality in the vicinity of
the development site.

10. Prevent/avoid
Reduce/
Minimise
Offset
Source
Pathway
Receptor
Passive
Active
Passive
Active
Passive
Active
Least Preferred
Most PreferredMitigation Option 1
Mitigation 1
Mitigation 2
Least Preferred
Mitigation Option 2
Mitigation Option 3
Mitigation Option 4
Mitigation Option 5
Mitigation Option 6
Mitigation Option 8
Mitigation Option 7

11. Using the Heirarchy - An Example
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• Redevelopment of the London Gate Business Park also known as ‘The Old Vinyl Factory’ due to the
site’s history; it was originally owned by British music company EMI and the location where iconic
records by The Beatles and Pink Floyd were pressed.
• Located in the London Borough of Hillingdon.
• Involved the demolition of existing buildings on site, construction to provide up to 510 residential
units, offices, retail, food outlets, an energy centre and car parking.
• Key sources of pollution to air:
• A new District Heating Network (DHN) plant,
• Traffic movements generated by the scheme (including those within ground-level, multi-storey and
basement car parks); and
• An adjacent railway line.
• An air quality assessment (modelling and monitoring) was undertaken covering:
• Air quality impacts on the surrounding area; and
• Site’s suitability for residential use in context of air quality.
• Planning permission was granted for the development in 2013.

12. Using the Heirarchy - An Example (contd)
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• Despite the fact that the EIA considered the air quality effects to be not significant, one of the
planning conditions required further mitigation to control pollution from the DHN plant due to its
proximity to the recently-designated Air Quality Focus Area in Hayes town.
• The DHN comprises a Combined Heat and Power (CHP) plant and five boilers – all gas-fired.
• The change in the predicted annual-mean NO2 concentration was 0 to 1% at nearby receptors and
the EPUK & IAQM impact descriptor ranged negligible to slight adverse.
• In other words, the DHN was expected to contribute a very small amount to future baseline NO2
concentrations.
• Using professional judgement, the air quality effect was considered not significant.
Long term average concentration
at receptor in assessment year
% Change in concentration relative to Air Quality Assessment Level
1 2-5 6-10 >10
75 % or less of AQAL Negligible Negligible Slight Moderate
76 -94 % of AQAL Negligible Slight Moderate Moderate
95 - 102 % of AQAL Slight Moderate Moderate Substantial
103 – 109 % of AQAL Moderate Moderate Substantial Substantial
110 % or more than AQAL Moderate Substantial Substantial Substantial

13. Prevent/avoid
Reduce/
Minimise
Offset
Source
Pathway
Receptor
Passive
Least Preferred
Most Preferred
Mitigation 2
This was a condition and the DHN had already been granted planning
permission as part of the proposal. Moreover, the DHN was required to meet
sustainability and carbon objectives.
Selective Catalytic Reduction would be implemented for the CHP reducing emissions
to 80 mg.m-3, well below the 95 mg.m-3 limit in the London Sustainable Design and
Construction Supplementary Planning Guidance (SPG). The design included low NOx
boilers with emissions below the 40 mg/kWh standard in the SPG.
In addition, emissions below the Air Quality Neutral benchmark for building emissions
in the SPG. No practical alternative to reduce NOx emissions further.
Not possible to relocate source of emissions as using an existing stack. Also,
not possible to increase the stack height as the location had restrictions – under
the Heathrow flight path.
The receptors affected were not within the developer’s control. Installation of
ventilation and NO2 filtration on third party building was not a viable option.
Valid approach in this case as further on-site mitigation was impractical and the
plant only contributed small amount to pollution levels. A Damage Cost
Assessment was used to estimate the monetary value of the AQ impacts from
the DHN. Total value of mitigation measures already proposed by the applicant
and an agreed financial contribution far exceeded this value. Council will use
the financial contribution towards measures to reduce pollution in the AQFA.
Using the Heirarchy - An Example (contd)
Least Preferred

14. Financial Contribution
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• Our involvement ended once the condition was discharged.
• Not able to comment on how the money was used but we note that Hillingdon’s 2017 Air Quality
Action Plan Progress Report states that contributions would “towards the costs of appropriate
mitigation measures including (but not limited to):
• highway works that alleviate congestion;
• improvement of traffic management systems to optimise traffic flow;
• implementation of regimes that encourage modal shift to less polluting modes of transport;
• specific measures which will reduce pollution emissions, for instance encouragement of use of Low
Emission Vehicles; and
• specific measures to be incorporated to protect existing receptors, for example, but not restricted
to, the use of green infrastructure at relevant locations. “