Positive proof - green space reduces air pollution

Preliminary results Green Space Test Measurement along motorway A50

Green space has a significant, positive effect on air quality - as shown by the preliminary results announced in June this year from the Green Space test measurement along the Dutch A50 motorway.

“Follow-up research should lead to better insight and eventually to the development of tools that can be applied in practice by local authorities in order to effectively utilize green space to improve air quality in their areas”, according to Jaap Modder, council chairman of the Urban region Arnhem-Nijmegen.

The test measurement shows that whilst vegetation is probably not suitable to improving air quality directly alongside the road, it can be used effectively to tackle pollution at local bottlenecks and traffic measures (such as speed limits) vegetation. Plus, the findings point to the use of green space being suitable for tackling background concentrations of pollution: the results of the test measurement clearly indicate that a part of the air pollution is eliminated by the vegetation. For nitrogen oxides a reduction of 13% (for broad-leaved trees) and 16% (for coniferous trees) was measured, with a margin for error of 4%. The methodology used in the test measurement turned out to be unsuitable for establishing the effect of vegetation on fine particles.

Research set-up

The Green Space test measurement was executed between May and December of 2008 and its objective was to provide an answer to the question whether green spaces alongside motorways affect the concentrations of fine particles and nitrogen oxides.
(Fine particles and nitrogen oxides are emitted by traffic and are detrimental to health and environment. Nitrogen dioxide originates in limited amounts from fuel combustion in an engine. It is, however, caused mainly by the emission of nitrogen monoxide which reacts in the air with ozone to produce the much more harmful nitrogen dioxide).

On the basis of millions of data, scientists compared the effect on vegetation with coniferous trees, with broad-leaved trees (lime trees) and with no vegetation. Never before has such a live test measurement been executed at this scale. The test measurement is nationally and internationally unique and as such fills a significant gap in the scientific knowledge of this subject.

Follow-up research

“We aim to offer the localities in our urban region practical tools to implement green space in environmental policy”, agrees Jan van der Meer, responsible for air quality in the Urban Region Arnhem-Nijmegen. “To that end, follow-up studies are necessary. Further data analysis should indicate how these processes evolve exactly and how the positive ‘sphere of influence’ of green space can be moved closer to the motorways. Does vegetation have a positive effect mainly on background concentrations in larger areas, or can we apply green space in cities to improve air quality there? In addition, we want to develop an alternative method for investigating the effect of vegetation on fine particles, an then apply it in a new test measurement.”

Consortium

The Green Space test measurement along the A50 was executed within the framework of the Eureka Programme Flora of the Urban Region Arnhem-Nijmegen. Flora is about green space as a tool to improve air quality in the urban region. The test has been executed by order of the Innovation Programme Air Quality of the Ministry of Transport and Communications and the Ministry of the Environment. This programme is aimed at a series of cost-effective measures for improving air quality along the national highways. The test measurement was executed by a consortium consisting of Wageningen University and Research, KEMA, Integralis PP and Urban Region Arnhem-Nijmegen.

For additional information, please contact Francien Rademaker of Urban Region Arnhem Nijmegen, telephone number +31 (0)24 – 329 79 73 or frademaker@destadsregio.nl