Clean Air Is Child Health Policy
Childhood asthma is the most common chronic disease of childhood in the United Kingdom, affecting roughly one child in eleven. It is also, on any international comparison, a condition we manage badly: England has one of the highest asthma mortality rates in Europe, fifty-four children died of asthma exacerbation in England between April 2019 and March 2023, and children in the most deprived areas are around four times more likely to die of an asthma attack than children in the least deprived. Emergency admissions for asthma among children under nineteen in England fell from 217 per 100,000 in 2014–15 to 122 in 2022–23, then rose again to 148 in 2023–24. The long improvement has stalled and begun to reverse. Eighty-seven per cent of the children who died had been prescribed three or more reliever inhalers in the preceding year — a marker of poor control visible in routine prescribing data well before the event.
Air pollution is not the only determinant of that burden, but it is the one most directly amenable to policy. Two claims need to be distinguished, because they carry different evidential weight and different economic implications.
The first is that air pollution triggers exacerbations in children who already have asthma. This is not contested. It is supported by daily time-series analyses linking pollution episodes to emergency attendances, by panel studies of symptoms in individual children, and by natural experiments — the 1996 Atlanta Olympics being the canonical case, where traffic restrictions cut peak ozone and paediatric asthma attendances fell, then recovered when the restrictions lifted. The response is measured in days.
The second claim is that pollution contributes to the development of asthma in the first place. This is stronger, newer, and no longer eccentric. Birth cohort studies find associations between early-life exposure to traffic-related pollutants and subsequent diagnosis; studies of children who move house find risk shifting with exposure. Modelling published in The Lancet Planetary Health attributed roughly four million new paediatric asthma cases worldwide each year to nitrogen dioxide. The remaining scientific dispute concerns magnitude, not direction.
Underlying both is a fact about developmental timing that is easy to overlook and that carries most of the economic weight. Children are not small adults. They breathe roughly twice as much air per kilogram of body weight, breathe faster, and are still building the gas-exchanging portion of the lung: a newborn has perhaps 20 to 50 million alveoli, an adult 300 to 500 million, and most of that construction occurs after birth and continues into adolescence. Lung function rises to a peak in the early twenties and declines thereafter. Roughly half of adults who develop chronic obstructive pulmonary disease arrive there not through accelerated decline but through a lower peak — reserve that was never built. Childhood exposure therefore does not merely cause childhood illness. It sets a ceiling that cannot be raised later.
The evidence that the damage is reversible
Until recently, the policy-relevant question was unanswered. Harm was well established; recovery was not. If deficits were fixed early and permanently, clean air policy would be a bequest to the unborn rather than an intervention with a measurable return.
The Southern California Children's Health Study provided the first strong evidence otherwise. As air quality in the Los Angeles basin improved across two decades, successive cohorts of children measured identically showed better lung function growth, and the proportion with clinically low lung function at fifteen fell from around 8% to under 4%.
The British replication arrived in August 2026. The CHILL study, published in The Lancet Public Health, followed more than 3,400 children aged six to nine across 84 primary schools in London and in Luton, a comparable urban area with no clean air zone. Baseline measurements were taken before London's Ultra Low Emission Zone opened in April 2019. Nitrogen dioxide exposure subsequently fell roughly twice as fast among the London children. Their lung function growth accelerated: the proportion with clinically impaired lung function fell from 14% to 9%, against 9% to 7% in Luton. London began materially worse and finished level.
Three qualifications belong with that result. Luton improved too, so part of the London gain reflects national trends and the pandemic. Total lung volume improved faster in London but had not fully converged, so the recovery was real and partial. And London introduced the zone alongside School Streets, Low Traffic Neighbourhoods and bus fleet renewal — the finding is properly read as the effect of a package. It is also worth noting that London's earlier Low Emission Zone, which covered only heavy vehicles and set undemanding standards, produced no detectable benefit to children's lungs. Stringency and coverage, not the existence of a scheme, determine whether anything happens.
What the economics turns on
The economic case for clean air policy is unusually sensitive to the appraisal boundary, and this — rather than any empirical parameter — is where most disagreement actually lives.
Four routes generate value. Avoided healthcare costs are the easiest to measure and the smallest: direct NHS asthma care across all ages runs at roughly £1.1 billion a year. Avoided productivity losses in the present are larger, since a child's exacerbation removes a parent from work, disproportionately mothers and single parents. Human capital effects — the association between childhood pollution exposure and cognitive development, attainment and later labour market outcomes — are almost always omitted and are plausibly the largest. Avoided future disease is the largest in expectation and the hardest to claim, materialising decades later and highly sensitive to the discount rate.
The scale of what a narrow boundary excludes is visible in the aggregates. The Royal College of Physicians puts the annual cost of air pollution to the UK at £27 billion, or up to £50 billion including wider impacts such as dementia, alongside roughly 30,000 attributable deaths. A 2024 analysis of the UK asthma pathway placed its ten-year net present value at £47 billion — of which around 77% is health-related quality of life and productivity loss rather than health service spending. An appraisal counting only NHS costs is not being conservative; it is examining under a quarter of the problem.
The distributional analysis deserves more honesty than it usually receives from either side. A flat daily charge is regressive in incidence: older, more polluting vehicles are disproportionately owned by lower-income households. The benefits, however, are strongly progressive, because exposure and vulnerability are jointly concentrated. People in the most deprived fifth of areas in England breathe PM2.5 concentrations around 8% higher than the least deprived, a gap showing no clear downward trend; ethnic minority populations face higher average exposure; and the CHILL study found pollution-related lung function deficits substantially larger in Asian and Black children than in White children. Transport for London's evaluation reported the largest reductions in exposure to illegal pollution levels in high-deprivation areas near major roads.
A policy with progressive benefits and regressive costs is not thereby vindicated. It is a policy requiring compensating transfers — scrappage support, exemptions, or revenue hypothecated to transport in affected areas — sized so that identifiable losers are made whole rather than informed that aggregate welfare has risen. Failure to design this in advance is the principal reason such schemes become politically fragile, and it is a design failure rather than a communications one.
Finally, the counterfactual. England's air is markedly cleaner than two decades ago: average PM2.5 exposure has more than halved, and almost the whole country is already below England's 2040 target of 10 µg/m³. That target, however, is twice the World Health Organization guideline of 5, and 96% of England remains above the WHO figure. The coroner in the inquest into the death of Ella Adoo-Kissi-Debrah — the first case anywhere in which air pollution was recorded on a death certificate — identified precisely this gap, in a Prevention of Future Deaths report issued in 2021 that remains substantially unactioned.
The implication for appraisal is that the do-nothing baseline is not stable. Paediatric asthma admissions are rising again, domestic wood burning has become the largest single source of UK PM2.5 emissions, and indoor air — where children spend around 90% of their time — remains effectively unregulated. Against a deteriorating counterfactual, the estimated benefit of acting is understated.
What the evidence now supports is a narrower and more defensible claim than advocacy usually makes: that stringent, comprehensive clean air zones measurably improve children's lung development within a small number of years, that the benefit accrues disproportionately to the worst-off, and that the economic case is strong when properly bounded and weak only when artificially narrowed to health service cash flows. That is sufficient to treat clean air as child health policy rather than environmental policy, and to place it in joint strategic needs assessments on those terms. It is not sufficient to treat the problem as solved, nor to substitute for the parallel track — asthma review, action plans, housing quality — on which the children already diagnosed depend.
