The effectiveness and acceptability of neighbourhood-level interventions to reduce outdoor air pollution: a systematic review

Background

Outdoor air pollution is a major public health concern, exacerbating health inequalities, and causing serious illness and death. A comprehensive evidence synthesis of neighbourhood-level outdoor air pollution reduction interventions was commissioned to inform local decision-making in the UK.

Methods

We searched 10 databases, reference lists, citations, and UK grey literature. We included quantitative, qualitative and observational studies examining the effectiveness and/or acceptability of neighbourhood-level interventions aimed at reducing human exposure to and health impacts of outdoor air pollution, compared with a separate site or pre-intervention control, on health and wellbeing outcomes and air quality. We applied narrative synthesis and best fit framework synthesis, informed by an a priori conceptual framework, to examine the impacts of interventions designed to prevent, mitigate and avoid air pollution.

Results

We examined 8912 records and 108 full texts from databases, 103 full texts from grey literature sources, 30 full texts from citation searches, and included 24 studies reported in 26 papers/reports. We identified a range of interventions, almost all traffic-related, implemented by different stakeholders. Low traffic neighbourhood and school streets interventions reduced air pollution levels and traffic counts, with little evidence of traffic spilling over to surrounding streets. Anti-idling messages reduced idling traffic. Walking school bus initiatives encouraged modal shift. Green wall interventions reduced air pollution, possibly depending on wind direction. Street adaptations had mixed effects on air pollution but reduced polluting traffic. A light-touch traffic calming intervention reduced traffic levels. An early warning system had a mixed impact on air pollution. Some studies lacked comparison sites and some may have been confounded by the COVID-19 pandemic.

Conclusions

A range of neighbourhood-level interventions have the potential to reduce outdoor air pollution locally. The most impactful appear to be low traffic neighbourhoods, school streets, anti-idling messages and green walls.