Air quality assessments under the Habitats Regulations are complicated by a number of factors. Recent case law decisions have established that the blind application of generic de minimis thresholds, which cannot be supported on logical or empirical grounds, is not consistent with the requirements of the Habitats Regulations. This talk will explore these decisions, in light of other case law, and will then summarise the approach taken to work commissioned by JNCC to derive decision-making thresholds which ensure sufficient protection to designated sites whilst avoiding legislative overkill.

1. Dr CAROLINE CHAPMAN MCIEEM
Director DTA Ecology Ltd
Co-Director DTA Publications Ltd
AIR QUALITY ASSESSMENT UNDER THE
HABITATS REGULATIONS
Decision making thresholds for ecological
assessments – where next?

2. Walking the line…
Netherlands
…where the conservation
status is unfavourable, the
possibility of authorising
activities [which add
further nitrogen loading]
seems necessarily limited .’
Boggis
It’s not that significant effects
are probable, a risk is sufficient’
... but must be ‘credible
evidence that there was a real,
rather than a hypothetical, risk’.
Sweetman
‘the need for an effect to be significant
lays down a de minimis threshold… If
all plans or projects capable of having
any effect whatsoever on the site were
to be caught by Article 6(3), activities
on or near the site would risk being
impossible by reason of legislative
overkill.’

3. Use of thresholds – the rumours…
•We can’t use thresholds anymore…
•everything has to be included in an in combination
assessment!

4. What happened in Wealden…
•1000AADT threshold rejected by Courts
•Knock on implications for 1% threshold
•lack of explanation…
‘Natural England’s advice cannot be supported on logical
and empirical grounds…
I believe that Natural England’s advice, brief as it was,
cried out for further explanation’

5. What happened in Wealden…
•Court also recognised…
‘…if it is known that specific impacts are very low indeed, or are likely to be
such, these can properly be ignored (e.g. if each AADT were known to be
20, it would require 50 of these to attain the threshold: depending on the
precise facts, a reasonable planning judgment could be made that 50 plans
or projects is inherently unlikely)’ (para 95)

6. The Dutch Nitrogen Ruling
CJEU Cases C-293/17 & C-293/18
Does the Habitats Directive preclude the use of thresholds per se?
‘The Habitats Directive must be interpreted as not precluding…. exempting
certain projects which do not exceed a certain threshold value or a certain limit
value… from the requirement for individual approval…
IF…
The national court is satisfied that the ‘appropriate assessment’ carried out in
advance, meets the criterion that there is no reasonable scientific doubt as to the
lack of adverse effects of those plans and projects on the integrity of the sites
concerned.
(para 104)
Habitats Directive does not preclude the exemption of certain
projects which do not exceed a certain threshold or limit value
where an assessment in advance demonstrates that there will be
no adverse effects from those plans and projects.

7. Use of thresholds…. where does that leave us?
• Effects which are ‘very small indeed’ can properly be
ignored…
• Thresholds are ok in principle but must be supported by
appropriate evidence base (‘assessment in advance’)…
Current difficulties stem from the lack of an agreed
approach as to how these should be identified
Leading to… the JNCC contract

8. The approach… First need to go back to basics
What is an ‘effect’ in HRA terms?
• HRA is not concerned with any effect at all but only with ‘likely
significant effects’.
• An effect is only ‘significant’ (in HRA terms) if it undermines the
conservation objectives… Waddenzee.
• Concept of site integrity also links back to conservation objectives
• Hence, a decision under HRA should focus on, and be limited to,
the qualifying features and the ability of a site to achieve its
conservation objectives.
• Not just any ‘effect’ on a site at all.

9. An important concept which underpins approach
• Effects which do not undermine the achievement of the conservation
objectives cannot therefore be ‘significant’.
• Where CL exceeded action to reduce emissions will always be targeted.
• Measures to reduce emissions are ‘on/off’ not ‘dial up/dial down’
• Unreasonable to argue that all sources making any contribution to an
exceedance must be reduced in a proportionate manner.
• Effects which do not undermine the delivery of (or ability to deliver)
targeted measures cannot be ‘significant’. Some small sources can
properly be ignored.

10. SITE
1. The further you
are from the site
the larger the area
of the ‘donut’
2. So… the number of
other plans and
projects within each
‘donut’ increases
exponentially with
distance
3. The closer a
source is to a site
the larger the
process contribution
4. The greatest
pollutant contribution
comes from the smaller
number of sources
closer to the site
A general principle?

11. Q: to what extent should
these sources influence
decision-making?
Measures to achieve the
conservation objectives will
be targeted to
large/medium sources
achieve the best outcomes.

14. So…. essentially
There is a contribution from very small proposals which
can ‘properly be ignored’ as it won’t represent a risk to
the achievement of the conservation objectives
•The approach seeks to define a level of change, over a
defined period of time, that will not undermine the
conservation objectives.
•Referred to as ‘Objective Compliant Change’
•From this value can derive decision-making thresholds

15. Terminology….
Term Working Definition
De minimis
Objective Compliant
Change
Decision Making
Threshold
Site-relevant
Threshold
A concept with refers to an overall quantum of change (however it arises) that is of
no consequence irrespective of other considerations.
A quantifiable contribution from an individual source, below which associated
effects can properly be ignored for the purpose of decision-making. The cumulative
effects of proposals excluded by it will not undermine the achievement of the
conservation objectives. Further assessment would not change the outcome of the
decision to be taken.
Taking account of site-specific considerations, a quantifiable contribution from an
individual source, below which associated effects can properly be ignored for the
purpose of decision-making. The cumulative effects of proposals excluded by it will
not undermine the achievement of the conservation objectives for the site
concerned.
A quantified magnitude of change, across a defined period of time, which will not
undermine the achievement of the conservation objectives for a designated site.

16. Over to Ben…

17. 12th October 2021
Dr Ben Marner
Decision-Making Thresholds for Air
Pollution Impacts on Nature
Conservation Sites

18. Consider Impacts from Unknown Future Projects in
combination with other Unknown Future Projects
‘OCC’
• The total ‘allowable’ adverse change
from all relevant projects in combination
‘DMT’
• How much each individual project can
contribute before the OCC is breached
‘SRT’
• As DMT but with site-specific factors
Assessment in Advance
Autonomous
Measures ‘Nitrogen
Futures’
Historic
Development
Density
How Plumes
Overlap
Uncertainty

19. All Models are Wrong (but Some are Useful)
• Recent
Predictions for
NOx are better
• NH3?
Roadside NO2 (>10 Years Ago)
Modelled Measured

20. Nitrogen Futures Baseline Modelling
2030 BAU (WM) 2030 NAPCP+DA
(NECR NOx)
Changes from 2017
to 2030 (kg-N/ha/yr)
https://jncc.gov.uk/our-
work/nitrogen-futures/
Only policies
already
adopted or
implemented
Includes
additional
measures to
meet NECR
targets
Business As
Usual With
Measures
National Air
Pollution
Control
Programme
(National
Emissions
Ceilings
Regulations)

21. -1.5
-1.4
-1.3
-1.2
-1.1
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
70% 75% 80% 85% 90% 95% 100%
Reduction
over
13
Years
(2017-2030)
kg-N/ha/yr
% of UK
Forecast Reductions in N Deposition
Short Vegetation from Nitrogen Futures
Total change over 13 years

22. -1.5
-1.4
-1.3
-1.2
-1.1
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
70% 75% 80% 85% 90% 95% 100%
Reduction
over
13
Years
(2017-2030)
kg-N/ha/yr
% of UK
2030 BAU (WM)
25% of NAPCP
50% of NAPCP
75% of NAPCP
2030 NAPCP+DA (NECR NOx)
Forecast Reductions in N Deposition
Short Vegetation from Nitrogen Futures

23. -1.5
-1.4
-1.3
-1.2
-1.1
-1
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
70% 75% 80% 85% 90% 95% 100%
Reduction
over
13
Years
(2017-2030)
kg-N/ha/yr
% of UK
2030 BAU (WM)
25% of NAPCP
50% of NAPCP
75% of NAPCP
2030 NAPCP+DA (NECR NOx)
Forecast Reductions in N Deposition
Reduction (in 1km2 Average N Dep) over at Least 90% of the UK
Short Vegetation
‘OCC’
‘DMT’
‘SRT’
X 0.2

24. Some Constraints
• 5 km ‘zone of perturbance’
• Exclude domestic combustion
• Exclude land-spreading
• Roads need a different approach
What a 5km radius circle looks like
Google Map data ©2021

25. Historic Project Density
(Powys Chickens)
Intersite-proximity of Planning Applications for Poultry
Sheds Granted in Powys 2015 – 2020
(small <40k birds) Google Map data ©2021
0
5
10
15
20
25
0 1 2 3 4 5 6 7 8 9 10 11 12
Number
of
Farms
Number of Other Consented Farms within 5km
All Farms Small Farms

26. ADMS-5 Dispersion Kernels
µg/m3 NH3
per kt Emission

27. Superimposed Dispersion Kernels
5 km radius
Sources placed at random
within 5 km r circle
Results summed at random
point

28. ‘OCC’
‘DMT’
‘SRT’
‘OCC’
‘DMT’
‘SRT’
0
2
4
6
8
10
12
14
16
18
20
0 10 20 30 40 50
In-combination
/
Individual
Maximum
Number of In Combination Sources
95th percentile – N dep (forest)
A
B DMT (N dep forest)
= OCC / (1+A)
SRT (N dep forest)
= OCC / (1+B)

29. Road Traffic
Forecast Annual Rates of Traffic
Growth in England, Scotland and
Wales 2011-2031 in NTEM V7
NTEM Planning Data Version 7 Guidance Note, 2016
Production Attraction

30. Road-NOx and Road-NH3
Relative change to Road-NOx, combining
range of NTEM V7 growth rates and EFT V10
Options
Relative change to Road-NH3, combining
range of NTEM V7 growth rates and CREAM
V1 Options

31. Road-N Deposition
Relative change to Nitrogen Deposition from
Roads (NTEM V7, EFT V10 + CREAM V1)

32. Thresholds for Road Traffic
• Small development are neither the problem nor the
solution
• Assessing them can distract from beneficial action
• Traffic threshold justified as a fraction of baseline traffic
growth
• Set as a % of AADT

33. Considers Impacts from Unknown Future Projects in
combination with other Unknown Future Projects
‘OCC’
• The total ‘allowable’ adverse change
from all relevant projects in combination
‘DMT’
• How much each individual project can
contribute before the OCC is breached
‘SRT’
• As DMT but with site-specific factors
Assessment in Advance
Autonomous Measures
‘Nitrogen Futures’
Historic Development
Density
How Plumes Overlap
Uncertainty
Roads based on relative contribution to problem (and solution)

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23 Coldharbour Road, Bristol BS6 7JT
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24 Greville Street, Farringdon, London, EC1N 8SS
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6 Bankside, Crosfield Street, Warrington, WA1 1UD
contact@aqconsultants.co.uk