Abstract
The benefits of ‘green infrastructure’ are multi-faceted and well-documented, but estimating those of individual street-scale planting schemes at planning can be challenging. This is crucial to avoid undervaluing proposed schemes in cost–benefit analyses, and ensure they are resilient to ‘value engineering’ between planning and implementation. Here, we introduce prototype software enabling urban practitioners to estimate the site-specific air quality impacts of roadside vegetation barriers: highly localised changes in pollutant concentrations due to changes in the dispersion of vehicular emissions close to source. We summarise the recent shift in understanding regarding the impacts of vegetation on urban air pollution towards changes in pollutant dispersion (cf. deposition) and describe our prototype software, offering rapid estimates thereof. First tests of the underlying model’s performance are promising, reproducing: annual mean NO2 and PM2.5 concentrations in a street canyon (Marylebone Road, London, UK) to within 10% and 25%, respectively; and changes in pollutant concentrations of the right order of magnitude behind roadside barriers in a wind tunnel simulation of a street canyon and a real open-road environment. However, the model underestimates the benefits of a barrier in a simulated street canyon under perpendicular wind conditions. The prototype software is a first step towards informing practitioners of the site-specific impacts of vegetation barriers, which should always be additional to (i.e., no substitute for) essential emission reductions. The code is open-source to engage further researchers in its continued development.
Highlights
Urban forests and ‘green infrastructure’ bring many benefits to our towns and cities, including increased biodiversity, sustainable urban drainage, mitigation of the urban heat island effect and improved air quality
We tend to categorise these benefits as environmental in kind, but, directly or indirectly, many of them translate to economic benefits via cost savings, such as reduced mains drainage costs, reduced indoor cooling costs and reduced health damage costs linked to air pollution
Recognition of the benefits, or ‘nature based solutions’ [11], delivered by this natural capital can support the preservation of existing green infrastructure and investment in further green infrastructure
Summary
Urban forests and ‘green infrastructure’ bring many benefits to our towns and cities, including increased biodiversity, sustainable urban drainage, mitigation of the urban heat island effect and improved air quality (see, e.g., [1,2,3,4]). Recognition of the benefits, or ‘nature based solutions’ [11], delivered by this natural capital can support the preservation of existing green infrastructure (e.g., justifying maintenance costs) and investment in further green infrastructure. It can be a challenge, for non-specialists to quantify at planning (including, but not limited to, the official process of obtaining planning permission) the environmental benefits, let alone the economic value, of an individual street planting scheme. We introduce prototype software enabling urban practitioners to estimate the site-specific air quality impacts of street planting at planning
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