Aerosol hygroscopicity is a critical parameter for predicting radiative forcing and climate sensitivity, particularly under sub-saturated regimes where it drives complex aerosol–water interactions. Here, we show that externally mixed aerosols exert a stronger influence on direct radiative forcing than is currently represented in models. Incorporating our findings into radiative forcing calculations indicates a stronger aerosol cooling effect, especially at suburban sites, highlighting the importance of representing regional differences in mixing state. The conventional bulk-chemistry approach, which assumes volume-based mixing with limited spatial variability, exhibits low predictive performance for aerosol hygroscopicity (R² ≈ 0.61) at urban and suburban sites. Using an interpretable machine learning framework trained on geographically diverse, region-specific datasets can capture this variability with higher accuracy (R² ≈ 0.97), identifying key chemical compositional and mixing-state drivers. (Figure presented.) ... Read more

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 synthesizing more than 500 relevant studies supplemented by diverse expert input. The result is a novel integrative framework that 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 esthetic preferences favoring 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 such as green bonds and debt-for-nature swaps offer promising mechanisms for resilient financing, while standardized 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 such as 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, emphasizing that effective GBI implementation demands context-specific strategies combining innovation, inclusive governance, and long-term stewardship to mainstream GBI in sustainable urban development. ... Read more

Understanding airborne particle mass deposition in the lungs is crucial for assessing health effects, particularly in regions with severe air pollution. While several studies have modelled lung deposition, there is limited information on lung tissue deposition that incorporates factors like hygroscopicity and density in polluted environments or source-specific exposures. This study examines the impact of atmospheric aerosol properties, including particle number size distribution, effective density, and hygroscopic growth, on lung tissue deposition using data from a measurement campaign in Delhi, India. Using the Hygroscopic Particle Lung Deposition (HPLD) model, the number (TDn) and mass (TDm) of tissue-deposited particles were calculated for various episodes: biomass burning (BB), chloride (Cl), hydrocarbon-like organic aerosol (HOA), and relatively clean (RC) periods. Chloride episodes, linked to industrial and waste burning activities, showed the highest tissue deposition mass (28 pg cm−2h−1), followed by BB (22 pg cm−2h−1), HOA (17 pg cm−2h−1), and RC (14 pg cm−2h−1) on total inner lung surface area. In addition, incorporating hygroscopicity and density increased deposition estimates by 1.8–2.8 times. This study underscores the importance of quantifying tissue deposition doses for improving exposure assessments, particularly in highly polluted regions where elevated particulate levels exacerbate lung inflammation, respiratory issues, and cancer risk. ... Read more

Low-cost air quality sensors (LCS) are increasingly used to complement traditional air quality monitoring yet concerns about their accuracy and fitness-for-purpose persist. This scoping review investigates topics, methods, and technologies in the application of LCS networks in recent years that are gaining momentum, focusing on LCS networks (LCSN) operation, drone-based and mobile monitoring, data fusion/assimilation, and community engagement. We identify several key challenges remaining. A major limitation is the absence of unified performance metrics and cross-validation methods to compare different LCSN calibration and imputation techniques and meta-analyses. LCSN still face challenges in effectively sharing and interpreting data due to a lack of common protocols and standardized definitions, which can hinder collaboration and data integration across different systems. In mobile monitoring, LCS siting, orientation, and platform speed are challenges to data consistency of different LCS types and limit the transferability of static calibration models to mobile settings. For drone-based monitoring, rotor downwash, LCS placement, flight pattern, and environmental variability complicate accurate measurements. In integrating LCS data with air quality models or data assimilation, realistic uncertainty quantification, ideally at the individual measurement level, remains a major obstacle. Finally, citizen science initiatives often encounter motivational, technological, economic, societal, and regulatory barriers that hinder their scalability and long-term impact. ... Read more

Urban greening plays a crucial role in enhancing climate resilience, environmental quality, public health, and societal wellbeing. Policy makers at all levels are increasingly embracing greening and other nature-based solutions; however, successful implementation of these approaches requires a multidisciplinary strategy involving collaboration, community engagement, and adaptive interventions. This paper synthesizes key insights from an expert panel, comprising representatives of government agencies, research institutions, private sector, and local authorities, forming an international panel of experts, convened by the RECLAIM Network Plus (https://www.reclaim-network.org). Funded by the United Kingdom Research and Innovation (UKRI), this network project brings together over 650 members from 40 plus countries. It provides national leadership in urban greening, serving as a “one-stop-shop” for towns and cities to access green and blue infrastructure support, resources, and peer connections. The paper highlights grand challenges, priorities, successful case studies and opportunities in urban greening initiatives. The importance of strategic planning is also addressed, together with technological advancements and access to suitable data for maximizing the impact of green infrastructure as well as innovative funding models, such as corporate social responsibility and green finance. This work highlights the importance of an integrated, inclusive, and forward-thinking approach to urban greening for more resilient, sustainable, and equitable cities. Further, it emphasizes the need for cross-sector collaboration among local authorities, researchers, and businesses, as well as community involvement in successful planning for both short- and long-term outcomes. Ultimately, urban greening strategies must be informed by future climate scenarios while prioritizing equity and social justice to ensure adaptation options benefitting all communities. ... Read more