Understanding the effect of built-up and green spaces upon air quality at multiple spatial scales: A systematic literature review

Understanding how to design and plan built-up and green spaces in cities is essential for achieving optimal outdoor air quality. While several studies have investigated how different indicators of built-up and green spaces impact air quality across various spatial scales (macro, meso, and micro), the findings and evidence remain fragmented and largely inaccessible to urban designers, planners, and policymakers. To bridge this gap, we conducted a systematic literature review of 61 peer-reviewed publications to: (1) provide an overview of the literature addressing the impacts of built-up and green spaces on air quality, including key areas of investigation (emission, dispersion, deposition, exposure, etc.), the pollutants studied (particulates, gases), and the quantitative methods used (numerical, physical, and empirical models); (2) develop a taxonomy of built-up and green space indicators that influence air quality at different spatial scales, such as urban canyon aspect ratios, vegetation size, and land-use and land-cover compositions; and (3) synthesize quantitative evidence on how these indicators affect air quality (positively, negatively, insignificantly, or variously) across scales. The taxonomy and synthesized evidence offer actionable, evidence-based insights for urban planning, design, and policy to improve air quality at different spatial scales. Additionally, the review highlights several under-explored areas for future air quality research, such as the impact of vegetation configuration.