Birmingham CAZ shows nitrogen dioxide reduction
Birmingham’s clean air zone (CAZ) has reduced the levels of nitrogen dioxide gas (NO2) by up to 7.3%, according to a new study.
University of Birmingham scientists discovered that during the CAZ’s first seven months of operation, after correction for weather and seasonal effects, it resulted in ‘modest, but significant’ reductions in NO2.
The scientists used a new method to strip out the effects of weather on air pollution levels, and then comparing the ‘de-weathered’ air pollution data in the Birmingham CAZ with those from cities with no CAZ, to quantify the ‘causal’ impact of the zone.
Their work, which is funded by Natural Environment Research Council and supported by Research England under the Policy Support funding stream, is part of the WM-Air project. The study provides a blueprint for cities across the UK and elsewhere to analyse their own clean air interventions.
Published in the journal Environmental & Resource Economics, the researchers reveal over the first seven months following the CAZ launch in June 2021, the biggest reductions in NO2 are at busy roadside locations within the CAZ with no significant changes at the urban background site located outside the CAZ.
They also found reductions in NO2 levels on roads outside the CAZ, suggesting behavioural changes contribute to reduced air pollution in surrounding areas, beyond the area of the CAZ itself.
Lead author Dr Bowen Liu, an assistant professor from the University of Birmingham, said: “Our work provides the first comprehensive evaluation of the Birmingham Clean Air Zone, an internationally significant policy to improve urban air quality in the UK’s second city. As predicted, Birmingham’s CAZ reduced NO2 pollution, but it has no detectable impact in the concentrations of fine particles, PM2.5 – the air pollutant with greatest health effects.”
Professor Zongbo Shi, a senior author who oversaw this work, added: “PM2.5 at monitoring sites in Birmingham still regularly exceed WHO air quality guideline levels, at which health impacts occur with significant health implications, including hundreds of premature deaths every year. More rigorous policy interventions – such as further local measures to reduce wood burning and agricultural emissions and nationally co-ordinated actions to mitigate secondary PM2.5 pollution – are needed to address non-vehicle sources of PM2.5 as quickly as possible.
‘Air pollution is one of the largest risks to the health of urban populations, with short- and long-term exposure shown to increase the risk of acute and chronic disease outcomes and reduce life expectancy. Improving air quality reduces healthcare costs, including to the NHS, and boosts economic productivity with lower levels of pollution-related illness.”
Co-authors Professors Rob Elliott and John Bryson said: “Tackling the air pollution challenge facing us requires an interdisciplinary approach, of which this research is an excellent example – drawing contributions from social, medical, and environmental sciences. Such an approach can also be used to inform the design and modification of existing or even proposed policy solutions.”
