London study finds Low Emission Zone has contributed to modest NOx reduction, with little effect on lung health of children
The introduction of the low emission zone (LEZ) in London, UK, has only contributed to modest reductions in exposure to NOx from diesel vehicles, and these improvements appear to have little effect on the lung health of children, according to an open-access observational study published in the journal The Lancet Public Health.
The study, which included more than 2,000 primary school children (aged 8-9 years) living in highly polluted areas of London’s low emission zone, confirmed that chronic exposure to common traffic-related pollutants is linked with reduced lung function.
Moreover, despite improvements in air quality following the introduction of the LEZ, the researchers found no evidence of a reduction in the proportion of children with small lungs or asthma symptoms over the 5 years since the scheme was implemented.
The research team from Queen Mary University of London, King’s College London and the University of Edinburgh said that the study highlights that despite European air quality policies and local measures, London’s air pollution may be putting children at risk of lifelong health problems, and underscores the need for more radical solutions to tackle high levels of air pollution. Early in 2019, London will introduce an Ultra Low Emission Zone, which is predicted to deliver major improvements in air quality.
In many areas of London, air pollution still remains a major issue. Some improvements in air quality have been made despite the diesel vehicles emitting higher levels of pollutants in the real world than in tests. Even so, many areas of inner and outer London are still breaching EU air pollution standards and are unlikely to meet them without a substantial tightening of current emission controls.—author Professor Chris Griffiths from Queen Mary University of London
Air pollution is linked to 7 million premature deaths worldwide every year (of these, 3.7 million are linked to outdoor air pollution). In the UK, air pollution contributes to 40,000 deaths each year, nearly a quarter of them in London. Across Europe, where more than half of new cars are fueled by diesel, NOx has become a major problem, and has been linked to asthma and impaired lung development in children.
Low emission zones have been widely promoted as the best way to tackle traffic pollution, with around 200 in operation across Europe. But little research has been done on the effectiveness of this approach at reducing air pollution and improving public health.
London introduced the world’s largest citywide low emission zone in stages during 2008 and 2012, requiring diesel vehicles entering Greater London to meet certain emission standards or pay daily charges—and providing a unique opportunity to investigate how effectively the initiative has improved air quality and children’s respiratory health.
The study included 2,164 children aged 8-9 years from schools close to air quality monitoring stations in four inner city London boroughs (Tower Hamlets, Hackney, Greenwich, City of London) in breach of EU annual nitrogen dioxide limits (40 μg/m³).
Between 2009-10 and 2013-2014, children were given yearly winter health checks that included measuring the size and function of their lungs by blowing into a machine called a spirometer. Parents were also asked to complete a medical history questionnaire for their child, including questions on respiratory and allergic symptoms (eg, asthma, eczema, hay fever).
Annual average exposure concentrations of NOx and particulate pollution (PM10 and PM2.5) were measured at the home and school addresses of each child over the 5-year study. The researchers also modeled pollution exposures for the 3 hours (0600-0900h), 24 hours, and 7 days before each child’s annual health check. This allowed them look at the effects of both short-term and annual average exposures simultaneously. They also took into account other factors that can affect respiratory health including age, sex, height, body mass index, ethnicity, socioeconomic status, and exposure to environmental tobacco smoke.
Results showed that introduction of the low emission zone had little impact in reducing levels of ultrafine particles (PM2.5) or course particulate matter (PM10) over the study period.
In contrast, levels of nitrogen dioxide at both the roadside and monitoring sites within and surrounding the study area fell by around 1 μg/m³ per year. Additionally, the proportion of children exposed to the EU annual nitrogen oxides limit fell from 99% (444/450 children) in 2009 to 34% (150/441) in 2013.
Nevertheless, average exposure levels of nitrogen dioxide over the 5-year study remained high (median 40.7 μg/m³) and the researchers estimate that children’s lung capacities were reduced by around 5%. They also noted some evidence of a reduction in rhinitis, but not asthma symptoms over the study period.
Although changes of this magnitude are unlikely to cause problems in healthy children, we urgently need to know whether these lung deficits will impact lung function and health in later life. Until longer-term impacts are known, doctors should consider advising parents of children with clinically significant lung disease to avoid living in highly polluted areas, or to adopt personal mitigation measures to limit their exposure. More research is needed to identify factors that lead to increased susceptibility or protection.—Professor Griffiths
The authors note that the study is observational, so no firm conclusions can be drawn about cause and effect. They also point to several limitations, including that the lack of a control group and pre-intervention health data mean that attribution of the changes in air quality and health to the low emission zone, and a direct evaluation of the health impact of the scheme, were not possible. They also note that the study began after the introduction of the initial phases of the scheme so the full effects might have been underestimated.
In a linked Comment to the paper, Dr. Hanna Boogaard, Health Effects Institute, US, discussed the challenges of conducting research into the health effects of air quality interventions. She concluded:
A key question that remains largely unresolved is whether NOx is a causal agent or only an indicator of traffic-related air pollution, given that correlations in space and time between concentrations of NOx and other traffic-related air pollutants are often high. The study by Mudway and colleagues adds to this quandary, and shows that more stringent measures to improve urban air quality and children’s health might be needed.
The study is a collaboration across the MRC Asthma UK Centre in Allergic Mechanisms of Asthma, the Asthma UK Centre for Applied Research and the MRC-PHE Centre for Environment and Health, and was funded by NHS Hackney, the NIHR Biomedical Research Centre at Guy’s and St Thomas’ NHS Foundation Trust and King’s College London with donations from Him Lee and the Felicity Wilde Charitable Trust.
Ian S. Mudway, Isobel Dundas, Helen E. Wood, Nadine Marlin, Jeenath B. Jamaludin, Stephen A. Bremner, Louise Cross, Andrew Grieve, Alex Nanzer, Ben M. Barratt, Sean Beevers, David Dajnak, Gary W. Fuller, Anna Font, Aziz Sheikh, Robert Walton, Jonathan Grigg, Frank J. Kelly, Tak Lee, Chris J Griffiths (2018) “Impact of London’s Low Emission Zone on air quality and children’s respiratory health” Lancet Public Health doi: 10.1016/S2468-2667(18)30202-0