Experimental investigation of green infrastructure for improving air quality in urban street canyons

<p dir="ltr">Quantification of pollutant reduction due to the presence of green infrastructure (GI) and their optimised design can improve air quality. Design and implementation of various GI options for improved air quality, specifically in street canyons, has not been explored. The overall objective of the thesis is to clarify the role of GIs on air quality improvement in street canyons. The approach started with a comprehensive literature review on air quality impacts of various GI in street canyons, followed by experimental investigations. Four experimental campaigns were conducted (i) to understand the pollution concentration and exposure variability in street canyons, (ii) to quantify the efficacy of a roadside hedge on air pollution reduction in a street canyon, (iii) to understand the influence of portable green barriers at a road traffic intersection, and (iv) to quantify the efficacy of green walls by assessment of deposition capacity of different species in relation to their morphological characters. All pollutant concentrations (PM₁, PM_2.5, PM₁₀: aerodynamic particle diameter 1 µ m; ≤ 2.5 µ m; ≤ 10 µ m respectively; PNC- Particle number concentration; BC- Black carbon) were higher and respiratory deposition doses for PM_2.5 and PM₁₀ for females during running (11±6 and 37±21 µgh^-1, respectively) were highest at street canyons in comparison with other urban microenvironments such as indoor, traffic intersections and parks. The presence of hedges in a street canyon revealed a reduction in concentrations of pollutants. BC showed a significant reduction at breathing height between -7 and -50%, and -15% for PNCs. Reduction in pollutant concentrations for heights between 1 and 1.7 m, with maximum reductions o f -16% (PM₁ and PM₁₀) and -17% (PM_2.5) at ~1 m height, was also observed. From the study on green walls, it is concluded that the combination of macro- and micromorphology of plant species determines its PM removal potential. This PhD thesis summarises the findings for the implementation of GIs on urban streets for improved air quality.</p>