Children's Health in London and Luton (CHILL)

Strong evidence links urban air pollution to restrictions in children's lung growth and development and other adverse effects, including increases in respiratory and allergy symptoms, respiratory infections, asthma, and health care use. Effective interventions are urgently needed that reduce air pollution and improve child health. Low Emission Zones (LEZ) are becoming widespread but are expensive to implement and of unproven health benefit. London has some of the worst air pollution in Europe. London's Ultra Low Emission Zone (ULEZ) is the central component of London's air quality strategy. Its implementation provides a unique opportunity to test the impact of a city-wide LEZ on children's health.

The intervention:

The ULEZ is an area within which all vehicles must meet exhaust emission standards or pay a daily charge to travel. It will be implemented and paid for by Transport for London. Starting in 2019, the ULEZ will initially cover London's central Congestion Charging Zone, an area bounded by the London Inner Ring Road, that includes the City of London plus adjacent areas of eight radially adjoining Boroughs. It is projected to deliver for central London by 2020 emission reductions of -49% for NOx; - 47% for NO2; and -11% for PM10. Subject to consultation, the ULEZ will subsequently extend to include an inner London area (within London's North and South Circular roads), and a London-wide area, for heavy vehicles only.

Questions:

1. What is the impact of the ULEZ on children's lung growth (the primary outcome)?
2. What is the impact of the ULEZ on secondary outcomes, including self-reported symptoms, respiratory infection, health care use and costs?
3. Does the ULEZ reduce health inequalities? 4) Is the ULEZ good value for money?

Study design:

Quasi-experimental study using a parallel cohort design. Population: 1520 children aged 6-9 yrs old, recruited in 26 London primary schools (school years 2, 3 and 4) in London's Central Ultra Low Emission Zone. Intervention: Ultra Low Emission Zone Comparison: 1520 children aged 6-9 yrs old, recruited in 26 primary schools (school years 2, 3 and 4) in Luton, matched for ethnicity, deprivation and baseline air quality.

Outcome: PRIMARY: Lung function growth (post-bronchodilator forced expiratory volume in one second (FEV1) measured by high quality spirometry at sequential annual school visits over four years. SECONDARY: Forced vital capacity (FVC), exhaled nitric oxide (FeNO), quality of life, respiratory infections, health care use, health costs.

Sample size:

To detect a 15ml/year FEV1 difference between central and outer London cohorts at 90% power and 0.05 significance requires children in each cohort, inflated to allow for clustering effect of schools, spirometry success, child and school attrition, and pre-specified sub group analyses, giving a total of 3120 children (60 children from 26 schools in each cohort).

Duration: 6 years Air quality data: Modeled exposures by London Air Quality Network Data management: NIHR accredited Pragmatic Clinical Trials Unit Analysis: Interaction analysis controlling for effect modifiers (eg passive smoke; ethnicity); health economic cost consequence analysis.