Traffic-related air pollution (TRAP) poses significant health risks particularly for children, with adverse effects that may impact health in later life. Low emission zones are a public health policy designed to reduce TRAP in urban areas. The CHILL (Children's Health in London and Luton) Study will evaluate the impact of London's Ultra Low Emission Zone (ULEZ) on children's health, using a prospective two-arm parallel longitudinal cohort design. CHILL will examine associations between air pollution metrics and lung function growth, plus secondary outcomes. Here we describe the characteristics of the CHILL cohort at baseline, prior to the introduction of the ULEZ. We recruited 3414 children aged 6-9 years attending 84 schools (London, intervention site: 1664 children, 44 schools; Luton, comparator site: 1750 children, 40 schools). Baseline health assessments were conducted in 2018-2019 (before the introduction of the ULEZ in London). 97.0% of recruited children were assessed (London 96.5%, Luton 97.4%), with the primary outcome measure of post-bronchodilator forced expiratory volume in one second being successfully measured in 76.7% (London 76.9%, Luton 76.5%). 92.1% returned a completed parental questionnaire (London 89.3%, Luton 94.7%), including data for analysis of the secondary outcomes. Demographic characteristics and outcomes were similar across the two sites. We established well-matched cohorts of school children, in our intervention (London) and comparator (Luton) sites. Data on primary and secondary outcomes have been successfully collected, which, combined with detailed air quality metrics, provides a robust platform for evaluating the impact of London's ULEZ on children's health and development.

The authors have declared no competing interest.

https://pubmed.ncbi.nlm.nih.gov/37925402/

This study was supported by the National Institute of Health Research Public Health Research (grant number 16/139/09) with additional funding by NIHR CLAHRC North Thames, Barts Charity, and NIHR ARC North Thames. EvS is funded by the Medical Research Council [MC UU 00006/5]. BM acknowledges support by the National Institute for Health Research Barts Biomedical Research Centre (NIHR203330). CJG is supported by the NIHR ARC North Thames. The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. Funders played no role in the design of the study and collection, analysis, and interpretation of data and in writing the manuscript.

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The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Queen Mary University of London Research Ethics Committee (ref 2018/08) and NHS West of Scotland Research Ethics Committee 4 (reference 22/WS/0065) gave ethical approval for this work.

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All data produced in the present study are available upon reasonable request to the authors