Cleaner Air Associated With Faster Lung Growth in London Children

Children living within London’s Ultra Low Emission Zone (ULEZ) showed significantly faster growth in postbronchodilator forced expiratory volume in 1 second (FEV₁) than children in the nearby town of Luton without a clean air zone. The –38 mL gap in FEV₁ between the 2 cohorts at baseline closed entirely within 4 years, according to a prospective cohort study published in The Lancet Public Health.¹

These findings, gleaned from the Children’s Health in London and Luton (CHILL) study, potentially offer new evidence that a clean air zone can measurably accelerate lung development in children, which is an outcome with a known link to chronic obstructive pulmonary disease, cardiometabolic disease, and premature mortality. The ULEZ was introduced in London in April 2019 and later expanded citywide.² It is now considered the world’s largest clean air zone, covering 1500 km² and a population of 9 million.

What Did the Data Show on Lung Growth?

Researchers recruited 3414 children aged 6 to 9 years from 84 primary schools between June 5, 2018, and April 4, 2019; 1664 children were from central London, and 1750 children were from Luton, 32 miles to the northwest, and all were recruited before ULEZ implementation. Fifty-six percent and 49% were female children.¹ The most common ethnicities in both groups were White (31% and 38%, respectively), Asian or Asian British (22% and 39%), and Black or Black British (19% and 8%). Smoking in the household was reported by 16% and 23%. Luton was selected because it shared a similar pollutant mix and demographic profile to London, despite lower overall pollution levels, and had no plans to enact its own low-emission zone.

Of the total study population, 3209 children (94%) had at least 1 FEV₁ measurement and were included in the primary analysis (1557, London; 1652, Luton). Parent-reported asthma diagnoses were more common among the Luton children (19%) vs the London children (9%), and both cohorts lived in areas of moderate socioeconomic deprivation. Lung function was measured annually via spirometry over 5 years, with an added year of data to compensate for COVID-19–related disruptions to school visits.

At baseline, children in London had significantly lower adjusted mean FEV₁ than children in Luton (difference, –38 mL; 95% CI, –58 to –18; P = .0002) and higher exposure to nitrogen dioxide (NO₂; difference, 18.95 µg/m³; 95% CI, 18.51-19.38; P < .0001). Over the next 4 years, FEV¹ grew by 223 mL/year in Luton but by an additional 10 mL/year in London (95% CI, 5-15; P = .0002). By the end of the study, the adjusted mean FEV1 was just about equal in the 2 cities:

• London: 2283 mL (95% CI, 2207-2354)
• Luton: 2282 mL (95% CI, 2185-2376)

Data on forced vital capacity (FVC) are also important to note. At baseline, FVC was 55 mL lower in London but increased 7 mL/year faster; however, after 4 years, the London children still had an FVC that was 25 mL lower than the Luton children: 2598 mL vs 2623 mL.

Further, the proportion of children with clinically impaired lung function—defined in the study as prebronchodilator FEV₁ below 80% predicted—fell from 184 of 1280 children (14%) to 51 of 585 children (9%) in London and from 126 of 1339 children (9%) to 41 of 606 children (7%) in Luton. The authors explained that these totals reflect both loss to follow-up and COVID-19–disrupted data collection.

Modeled residential NO₂ exposure fell faster in London than in Luton, by 2 µg/m³ per year (95% CI, –2.21 to –1.78; P < .0001)—3.77 vs 1.77, respectively—a pattern the researchers linked to the ULEZ’s targeting of exhaust emissions. An interquartile range increase in NO₂ exposure was associated with a decrease in FEV₁ growth of –21.46 mL/year (95% CI, –26.41 to –16.51) across the full cohort, with Asian and Black children showing significantly larger pollution-related growth deficits than White children (P < .05) according to an exploratory subgroup analysis.

The Policy Implications

“The observed improvements could potentially prevent long-term adverse health impacts in adulthood, including premature mortality,” the authors concluded. “These findings support the wider use of effective clean air zones as a public health policy intervention to improve the lung health of children in cities.” They highlighted that although FEV₁ reached parity, FVC did not.

They are extending follow-up of the CHILL cohort into adolescence because they want to determine if “continued exposure to less polluted air produces further improvements” and to examine ongoing pollution trends,¹ noting that their findings align with prior research in North America and Sweden linking improved air quality to better lung function growth in children and adolescents.^3,4 Air pollution exposure before and after birth has also been linked to increased respiratory infection risk and impaired lung function in children up to age 9 years.⁵

Lead author Helen E. Wood, DPhil, project manager for the London arm of CHILL, spoke to findings from CHILL at the American Thoracic Society 2026 International Conference. She explained, “What we can imply from that is that effectively implemented clean air zones can impact on a critical component of children’s development with the potential to prevent long-term adverse health impacts in adulthood, including premature death. Cities across the world with significant traffic-related air pollution could benefit from implementing effective clean air zones.”⁶

Limitations on these findings include possible self-selection bias, the high attrition rate, having only 2 study sites, schools and children not being fully representative, and unmeasured reasons for different lung growth.

References

1. Wood HE, Hajmohammadi H, Dove RE, et al. Impact of the Ultra Low Emission Zone on lung function growth in children in London, UK: a prospective parallel cohort study. Lancet Public Health. 2026:S2468-2667(26)00163-5. doi:10.1016/S2468-2667(26)00163-5
2. Ultra Low Emission Zone. May of London. Accessed August 19, 2026. https://tfl.gov.uk/modes/driving/ultra-low-emission-zone
3. Gauderman WJ, Urman R, Avol E, et al. N Engl J Med. 2015;372(10):905-913. doi:10.1056/NEJMoa1414123
4. Yu Z, Merid SK, Bellander T, et al. Associations of improved air quality with lung function growth from childhood to adulthood: the BAMSE study. Eur Respir J. 2023;61(5):2201783. doi:10.1183/13993003.01783-2022
5. Santoro C. Elevated respiratory infection risk in pediatric populations associated with ambient air pollution. AJMC^®. July 11, 2025. Accessed August 19, 2026. https://www.ajmc.com/view/elevated-respiratory-infection-risk-in-pediatric-populations-associated-with-ambient-air-pollution
6. Bonavitacola J. Clean air zones can affect children’s development in New York, London. AJMC. May 18, 2026. Accessed August 19, 2026. https://www.ajmc.com/view/clean-air-zones-can-affect-children-s-development-in-new-york-london