Impact of London's low emission zone on air quality and children's respiratory health: a sequential annual cross-sectional study

Abstract

Background: Low emission zones (LEZ) are an increasingly common, but unevaluated, intervention aimed at improving urban air quality and public health. We investigated the impact of London's LEZ on air quality and children's respiratory health.

Methods: We did a sequential annual cross-sectional study of 2164 children aged 8-9 years attending primary schools between 2009-10 and 2013-14 in central London, UK, following the introduction of London's LEZ in February, 2008. We examined the association between modelled pollutant exposures of nitrogen oxides (including nitrogen dioxide [NO₂]) and particulate matter with a diameter of less than 2·5 μm (PM_2·5) and less than 10 μm (PM₁₀) and lung function: postbronchodilator forced expiratory volume in 1 s (FEV₁, primary outcome), forced vital capacity (FVC), and respiratory or allergic symptoms. We assigned annual exposures by each child's home and school address, as well as spatially resolved estimates for the 3 h (0600-0900 h), 24 h, and 7 days before each child's assessment, to isolate long-term from short-term effects.

Findings: The percentage of children living at addresses exceeding the EU limit value for annual NO₂ (40 μg/m³) fell from 99% (444/450) in 2009 to 34% (150/441) in 2013. Over this period, we identified a reduction in NO₂ at both roadside (median -1·35 μg/m³ per year; 95% CI -2·09 to -0·61; p=0·0004) and background locations (-0·97; -1·56 to -0·38; p=0·0013), but not for PM₁₀. The effect on PM_2·5 was equivocal. We found no association between postbronchodilator FEV₁ and annual residential pollutant attributions. By contrast, FVC was inversely correlated with annual NO₂ (-0·0023 L/μg per m³; -0·0044 to -0·0002; p=0·033) and PM₁₀ (-0·0090 L/μg per m³; -0·0175 to -0·0005; p=0·038).

Interpretation: Within London's LEZ, a smaller lung volume in children was associated with higher annual air pollutant exposures. We found no evidence of a reduction in the proportion of children with small lungs over this period, despite small improvements in air quality in highly polluted urban areas during the implementation of London's LEZ. Interventions that deliver larger reductions in emissions might yield improvements in children's health.

Funding: National Institute for Health Research Biomedical Research Centre at Guy's and St Thomas' National Health Service (NHS) Foundation Trust and King's College London, NHS Hackney, Lee Him donation, and Felicity Wilde Charitable Trust.

Figure 1

Study flowchart FEV₁=forced expiratory volume in 1 s.

Figure 2

Study timeline and annual NO₂ models The upper panel shows the study timeline relative to the various phases of the London low emission zone (appendix 1 p 4). The shaded areas represent the annual collection windows, which ran over the winter periods. The lower panels represent the annual NO₂ pollution maps (2008–13) used for the exposure assessments. NO₂=nitrogen dioxide. LEZ=London emission zone.

Figure 3

Running annual mean NO_x (A) and NO₂ (B) concentrations at London roadside and background sites from 2006 to 2014 Background sites are within and surrounding the study area. Air pollution is shown relative to the three phases of the LEZ (appendix 1 p 4). Forest plots for roadside and background NO_x (C, D) and NO₂ (E, F) across the period 2008–13 by site and aggregated across sites (RE, refers to the overall trend). Data are presented as the median of the slopes between all pairs of points from the monthly mean concentration time series; 95% CIs were calculated by bootstrap sampling. NO_x=nitrogen oxides. NO₂=nitrogen dioxide. LEZ=London emission zone. RE=random effect.

Figure 4

Change in FEV₁ (A–D) and FVC (E–H) per unit change in NO_x, NO₂, PM₁₀ and PM_2·5 annual concentrations Analyses were based on residential address or were weighted for periods spent at home and school addresses. Data are mean (95% CI) for each study year, plus the pilot, and aggregated across study years 1–5. FEV₁=forced expiratory volume in 1 s. NO_x=nitrogen oxides. NO₂=nitrogen dioxide. PM₁₀=particulate matter with a diameter of less than 10 μm. PM_2·5=particulate matter with a diameter of less than 2·5 μm.

Figure 5

Associations of the four selected pollutants with FEV₁ and FVC, with 3 h (0600–0900 h), 24 h, 7 day, and annual exposure attributions Analyses were based on residential address and were weighted for periods spent at school. Data are presented as mean (95% CI) pooled across years 1–5. FEV₁=forced expiratory volume in 1 s. FVC=forced vital capacity. NO_x=nitrogen oxides. NO₂=nitrogen dioxide. PM₁₀=particulate matter with a diameter of less than 10 μm. PM_2·5=particulate matter with a diameter of less than 2·5 μm.