The Pollution They Don’t Measure: Folkestone & Hythe’s PM2.5 Blind Spot From Wood Burners to Otterpool Park

Folkestone & Hythe District Council can tell residents what nitrogen dioxide was beside a particular road to a tenth of a microgram. What it still cannot tell them is how much PM2.5 they actually breathed there.

That is the gap at the centre of the district’s air-quality story.

FHDC’s latest annual report states plainly that there is no direct monitoring of either PM10 or PM2.5 anywhere in the district. Instead, it relies on Defra computer-modelled background concentrations.

For 2025, the highest modelled PM2.5 background concentration is 7.2µg/m³ in east Folkestone, around the harbour, A260 and A2033.

That 7.2 is not a monitor reading. It is a modelled estimate.

The World Health Organization recommends annual averages of 5µg/m³ for PM2.5, 15 for PM10 and 10 for nitrogen dioxide. Those are health-based recommendations, not legally binding UK limits. WHO itself says its guidelines are advisory tools for setting policy and legislation.

On that comparison, FHDC’s highest modelled PM2.5 background concentration is 44% above the WHO annual guideline.

Legal air and healthy air are not the same thing

FHDC’s actual monitoring contains good news.

Nitrogen dioxide is physically monitored using diffusion tubes. The highest annual reading has fallen from 30µg/m³ in 2019 to 19 in 2025.

None of the 2025 sites breached the UK annual NO₂ objective of 40.

That is why FHDC says years without an NO₂ exceedance mean the district is considered to have “good air quality”.

But WHO’s annual health guideline is 10.

Of 20 usable FHDC NO₂ results for 2025, 18 were above that level.

And after two years of broad improvement, the direction changed. In 2024, 88% of comparable locations recorded lower NO₂. In 2025 just five of 17 — 29% — improved. Eleven worsened and one was unchanged.

So the evidence does not say Folkestone & Hythe’s air is relentlessly getting worse. Measured NO₂ has improved substantially over the longer term.

But legally compliant does not necessarily mean within the concentrations recommended on health grounds.

The pollutant FHDC does not measure

PM2.5 is different.

FHDC’s own report says fine particulate pollution has significant effects on human health, including premature mortality. It records that 4.9% of mortality in Folkestone & Hythe is attributable to PM2.5.

Yet there is no FHDC PM2.5 monitor producing a local annual concentration.

That becomes more significant when placed beside another The Shepway Vox Team’s investigation into domestic wood burning.

Our previous work identified 1,356 recorded stove-related installation events between December 2020 and December 2025. A separate estimate suggested around 5,644 stoves across the district — roughly 16.4% of homes.

The figures measure different things, but both point towards substantial local stove use.

Defra says domestic combustion contributed 20% of UK PM2.5 emissions in 2024, with indoor wood burning alone contributing 12%. Road transport contributed another 21%, much of it now from brake, tyre and road wear rather than exhausts.

FHDC has no Smoke Control Areas. Its latest report records 123 smoke complaints during 2025, although it warns the figure contains logging inaccuracies and duplicates. No formal smoke notices were served.

None of this proves wood burners caused any individual case of asthma, COPD or other illness.

But wood burning is a recognised PM2.5 source, and FHDC has no direct particulate monitoring network capable of showing where concentrations rise, what happens on winter evenings, or whether areas with greater domestic burning experience higher PM2.5.

How did Otterpool’s PM2.5 fall 40% without anybody measuring it?

Otterpool Park makes that monitoring gap difficult to ignore.

The original March 2022 air-quality assessment explicitly acknowledged that FHDC and Ashford Borough Council did not monitor PM10 or PM2.5.

Arcadis recognised a lack of local-authority baseline monitoring around the development and conducted additional monitoring.

But those monitors measured NO₂.

Particulate pollution remained modelled.

In the 2022 assessment, the modelled average 2024 background PM2.5 concentration was approximately 9.23µg/m³.

The 2026 addendum gives an average for that same 2024 baseline year of 5.5µg/m³.

That is roughly 40% lower.

But no PM2.5 monitor recorded a 40% fall.

The modelling changed.

The 2026 assessment uses newer Defra background maps, a newer emissions toolkit and updated conversion tools. It also says an uplift previously applied because of uncertainty over future vehicle emissions is no longer being used.

The two figures therefore do not demonstrate that Otterpool’s actual PM2.5 fell by 40%. They are outputs from different modelling exercises using different assumptions and inputs.

That distinction is crucial.

The 2022 report itself warned that Defra background modelling could be overly optimistic and applied a 1.16 uplift during its modelling process.

Even under the newer, lower model, Otterpool’s highest future PM2.5 concentrations are predicted at 5.5µg/m³ in 2035 and 5.7 in 2055 — both above WHO’s annual guideline of 5.

Again: modelled, not measured.

Twenty-eight years of construction

The updated Otterpool programme anticipates construction from 2028 to 2056 — approximately 28 years.

The assessment recognises fugitive dust from demolition, excavation, earthworks, construction, storage and vehicle movements. More than 100 existing receptors lie within 20 metres for the purposes of its dust assessment.

Before mitigation, human-health dust risk is rated medium across demolition, earthworks, construction and trackout, while dust-soiling risk is high for earthworks and construction.

Mitigation is proposed.

But for a project lasting nearly three decades, the evidence supporting those assumptions matters.

The law does not stop at “below the limit”

The Supreme Court’s judgment in R (ClientEarth) v Secretary of State [2015] UKSC 28 concerned legally binding NO₂ requirements. It did not make WHO guidelines binding and does not automatically make Otterpool unlawful.

Nor does planning law impose an automatic moratorium on development wherever pollution is a concern. The Court of Appeal rejected that proposition in Shirley and Rundell [2019] EWCA Civ 22, a case concerning 4,000 homes at Canterbury.

But Gladman Developments Ltd v Secretary of State [2019] EWCA Civ 1543, involving housing at Newington in Swale, shows the other side of the equation. The Court of Appeal upheld an inspector’s approach where air-quality harm was identified and the effectiveness of proposed mitigation had not been satisfactorily demonstrated.

The lesson is not that Otterpool must be refused.

It is that future improvements and mitigation have to withstand proper evidential scrutiny.

And national planning policy has now tightened.

The National Planning Policy Framework published on 29 September 2026 says development must consider the cumulative effects of pollution on health and particularly vulnerable people such as children and older residents. It requires proposals to “sustain and contribute to compliance” with relevant air-quality objectives and targets, expressly including PM2.5.

England also has legally binding PM2.5 targets: annual mean concentrations of 10µg/m³ or lower by 2040, and a 35% reduction in population exposure compared with 2018.

Government planning guidance says cumulative development matters and asks how schemes will reduce PM2.5 exposure for residents, schools and other receptors.

That makes the unanswered question sharper:

For a development expected to be under construction for nearly three decades, is modelling alone sufficiently robust when the district has no local PM2.5 monitoring network against which those models can be tested — particularly when the 2022 and 2026 assessments produce dramatically different answers for the same baseline year?

The health burden is already here

Kent’s 2025 Pharmaceutical Needs Assessment estimates 121,000 Kent residents live with asthma or COPD/respiratory disease.

Folkestone & Hythe’s age-standardised prevalence is around 7.5%, significantly above Kent’s 6.9%.

That does not establish causation. Smoking, age, deprivation, housing conditions, occupational exposure and other factors all matter.

But it makes the absence of direct particulate monitoring harder to dismiss as a technical detail.

After years of annual air-quality reports, two major Otterpool assessments and repeated acknowledgement of the health effects of PM2.5, Folkestone & Hythe and its Cabinet member for Air Quality Cllr Stephen Scoffham still cannot produce one directly measured district PM2.5 annual concentration.

For a pollutant linked in the council’s own report to premature mortality, that is not a small gap in the data.

It is the missing measurement at the centre of the story.

The Shepway Vox Team

Deliciously Different Dissent