Green infrastructure (GI) includes trees, hedges,
individual shrubs, green walls, and green roofs.
GI offers many different benefits or services,
including flood risk mitigation, microclimate regulation, carbon sequestration, improved health
and wellbeing and ? the focus of this document
? air pollution abatement. Air pollution comprises variable quantities of many different types of
pollutants, including gaseous pollutants, such as nitrous oxides (NOx) and particulate matter (PM),
which is composed of particles such as black
carbon (BC). Road traffic is a dominant source of
air pollution in urban areas globally. In near-road
environments, vegetation can act as a barrier
between traffic emissions and pedestrians
(figure below), by collecting pollutants and/or
redirecting the flow of polluted air.
This document summarises best practice regarding GI implementation for improved urban
air quality and reduced pedestrian exposure
to air pollution. Generic (i.e. not site-specific)
recommendations are offered for typical urban
environments. These recommendations are
based upon contemporary scientific evidence
and knowledge, and may therefore be subject
to modification as the evidence base develops.
This guidance document consolidates major
findings from relevant publications, including a
detailed report on the relationship between vegetation and urban air quality, review articles
and other guidance documents.
Vegetation can form a barrier between traffic emissions and adjacent areas, but the optimal configuration and plant composition of such green infrastructure (GI) are currently unclear. We examined the literature on aspects of GI that influence ambient air quality, with a particular focus on vegetation barriers in open-road environments. Findings were critically evaluated in order to identify principles for effective barrier design, and recommendations regarding plant selection were established with reference to relevant spatial scales. As an initial investigation into viable species for UK urban GI, we compiled data on 12 influential traits for 61 tree species, and created a supplementary plant selection framework. We found that if the scale of the intervention, the context and conditions of the site, and the target air pollutant type are appreciated, the selection of plants that exhibit certain biophysical traits can enhance air pollution mitigation. For super-micrometre particles, advantageous leaf micromorphological traits include the presence of trichomes and ridges or grooves. Stomatal characteristics are more significant for sub-micrometre particle and gaseous pollutant uptake, although we found a comparative dearth of studies into such pollutants. Generally advantageous macromorphological traits include small leaf size and high leaf complexity, but optimal vegetation height, form and density depend on planting configuration with respect to the immediate physical environment. Biogenic volatile organic compound and pollen emissions can be minimised by appropriate species selection, although their significance varies with scale and context. While this review assembled evidence-based recommendations for practitioners, several important areas for future research were identified.
Kumar Prashant, Hama Sarkawt, Omidvarborna Hamid, Sharma Ashish, Sahani Jeetendra, Abhijith K.V, Debele Sisay E., Zavala-Reyes Juan C., Barwise Yendle, Tiwari Arvind (2020) Temporary reduction in fine particulate matter due to ?anthropogenic emissions switch-off? during COVID-19 lockdown in Indian cities, Sustainable Cities and Society 102382
The COVID-19 pandemic elicited a global response to limit associated mortality, with social distancing and lockdowns being imposed. In India, human activities were restricted from late March 2020. This ?anthropogenic emissions switch-off? presented an opportunity to investigate impacts of COVID-19 mitigation measures on ambient air quality in five Indian cities (Chennai, Delhi, Hyderabad, Kolkata, and Mumbai), using in-situ measurements from 2015 to 2020. For each year, we isolated, analysed and compared fine particulate matter (PM2.5) concentration data from 25 March to 11 May, to elucidate the effects of the lockdown. Like other global cities, we observed substantial reductions in PM2.5 concentrations, from 19 to 43% (Chennai), 41?53 % (Delhi), 26?54 % (Hyderabad), 24?36 % (Kolkata), and 10?39 % (Mumbai). Generally, cities with larger traffic volumes showed greater reductions. Aerosol loading decreased by 29 % (Chennai), 11 % (Delhi), 4% (Kolkata), and 1% (Mumbai) against 2019 data. Health and related economic impact assessments indicated 630 prevented premature deaths during lockdown across all five cities, valued at 0.69 billion USD. Improvements in air quality may be considered a temporary lockdown benefit as revitalising the economy could reverse this trend. Regulatory bodies must closely monitor air quality levels, which currently offer a baseline for future mitigation plans.