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Rapid urbanisation in tropical megacities intensifies critical environmental stressors, including urban overheating, particulate air pollution (PM2.5 and black carbon (BC)), and noise. Green-Blue-Grey Infrastructure (GBGI) offers a promising nature-based solution, yet major knowledge gaps exist regarding its empirical, multifunctional performance and diurnal dynamics in complex tropical settings. This study quantifies how vegetation in a large urban park (Ibirapuera Park, São Paulo) moderates microclimate, improves air quality, and attenuates noise, while assessing the influence of canopy structure and spatial location on these benefits. A comprehensive mixed-method approach was employed during a 15-day intensive field campaign. High-resolution spatiotemporal data on PM2.5, BC, carbon dioxide (CO2), noise, and meteorological parameters were collected through a combination of stationary monitoring at nine ecologically distinct sites and mobile transect monitoring across an urban-park gradient. These observations were complemented by thermal imagery and sky view factor (SVF) analysis. The park delivered substantial and dynamic environmental benefits. Dense vegetation reduced PM2.5 and BC by up to 40%, with mobile gradients of 0.07 and 0.03  µg m⁻3 per 100  m toward the park core, respectively. Cooling averaged 1–2 °C, strengthening to 0.2 °C per 100  m outward in afternoons. A distinct temporal duality emerged: peak cooling occurred in the afternoon, while the strongest air quality improvements occurred in the morning before dense canopy began retaining pollutants. Noise attenuation was modest (∼6 dB), with reductions of 0.29  dB and 0.25  dB per 100  m in morning and afternoon transects. Overall, the park functions as a multifunctional environmental regulator, with benefits shaped by vegetation density, spatial configuration, and time of day. Effective GBGI planning in tropical megacities should prioritise deep vegetative cores (≥250–300  m from major roads), multi-tiered buffers along traffic corridors, and dense canopy structures (SVF 

While outdoor urban greening is recognised for its benefits, indoor green infrastructure (iGI) in shaping indoor environmental quality (IEQ) - including air quality, thermal comfort, and bioaerosols - remains underexplored. This ten-question paper identifies key challenges, opportunities, and research gaps in the iGI-IEQ nexus, organised under 10 questions across five thematic clusters: (1) biophysical and technical performance; (2) ecological and microbiological dynamics; (3) human health and wellbeing; (4) equity, access, and socio-economic factors; and (5) implementation and systems integration. Findings indicate that iGI can improve air quality, regulate humidity, and enhance thermal comfort. However, its performance depends strongly on plant density, species selection, and ventilation. Most evidence comes from controlled settings. iGI may offer positive psychological and cognitive benefits, and can reduce health inequalities through affordable indoor interventions. However, significant data scarcity exists for long-term field studies, indoor microbial ecosystem effects, and socio-economic accessibility. Widespread adoption of iGI requires quantification of proven benefit conditions, followed by overcoming technical, operational, and regulatory barriers via adaptive design, digital monitoring, and interdisciplinary collaboration. As a culminating synthesis, this study introduces a newly developed comprehensive matrix that classifies twenty-six indoor greening types across twenty IEQ parameters, incorporating an assessment of current data confidence. This matrix lays a foundational framework for informed decision-making and design guidance. This review offers evidence-based insights for researchers, policymakers, and practitioners to effectively leverage iGI where suitable, in creating healthier, climate-resilient residential and commercial buildings, addressing both immediate IEQ challenges and supporting long-term sustainability objectives.

Green and blue infrastructure (GBI) is emerging as a key strategy for climate adaptation and urban resilience, yet its implementation often faces critical contextual barriers. This review initially screened over 29,000 publications, ultimately synthesising more than 500 relevant studies supplemented by diverse expert input. The result is a novel integrative framework connects previously siloed knowledge and consolidates 21 underexplored barriers across four key domains of GBI implementation: environmental, social, economic, and governance/policy. Environmental barriers include conflicts between GBI and renewable energy goals, specifically photovoltaics, unintended consequences of GBI (such as allergenic pollen production), urban ventilation disruption, and vulnerability of plant species to multiple urban stressors. Effective responses include thoughtful allocation and integration of photovoltaics and GBI, developing context-specific frameworks combining ecological knowledge with technological innovation, fostering cross-disciplinary collaboration across technical and social domains, science-based species selection and implementing multi-scalar strategies that enhance ecological connectivity. Social barriers encompass environmental injustice, cultural disconnection, limited public adoption, safety concerns, and aesthetic preferences favouring manicured over ecologically functional landscapes. These challenges highlight the need for participatory design, culturally responsive planning, and inclusive resource allocation to strengthen community engagement and long-term stewardship. Economic barriers stem from biodiversity undervaluation, inadequate asset recognition in accounting frameworks, incomplete cost-benefit analyses, and limited private investment. Innovative financing tools like green bonds and debt-for-nature swaps offer promising mechanisms for resilient financing, while standardised natural capital accounting frameworks can better capture GBI's multifunctional value. Governance barriers include land scarcity, urban design limitations, policy fragmentation, and disconnects with other urban agendas like walkability. Overcoming these requires institutional realignment, cross-sectoral collaboration, and integrated spatial planning. The review unifies these findings into 12 actionable recommendations to support holistic decision-making, emphasising that effective GBI implementation demands context-specific strategies combining innovation, inclusive governance, and long-term stewardship to mainstream GBI in sustainable urban development. [Display omitted]