Vertical greening systems with native species: an ecological approach to urban air quality improvement

Urbanization and climate change have intensified environmental challenges that pose significant risks to human health. Green infrastructure (GI), such as vertical greening systems (VGS), offers nature-based solutions to improve air quality, mitigate the urban heat island effect, and enhance biodiversity. Despite their benefits, VGS implementation is often constrained by maintenance challenges, species selection issues, and a lack of ecological considerations. This study explores the particulate matter (PM) retention capacity of native plant species that naturally colonize urban walls, evaluating their potential suitability for integration in VGS as a nature-based strategy to enhance air quality in urban environments while promoting biodiversity conservation. A case study in Rome evaluated five native plant species—Cymbalaria muralis, Capparis spinosa, Centranthus ruber, Parietaria officinalis, and Rubus ulmifolius—based on their efficiency in capturing PM. The research proposes a framework for selecting native species with differing leaf microstructural characteristics (e.g., wax density, trichomes, and surface wettability) and explores their potential role in PM retention, without quantitatively measuring these traits as explanatory variables. Using scanning electron microscopy (SEM) , the study quantified PM accumulation on leaves collected from multiple sites. Statistical analyses showed that C. ruber exhibited the highest overall PM capture efficiency, whereas P. officinalis demonstrated the lowest. C. muralis and C. spinosa captured significantly greater amounts of fine particles (<1 µm). The findings suggest that native species may offer promising potential for integration in VGS to support urban air quality improvement, while their adaptation to local climatic conditions could contribute to reduce maintenance requirements. The study highlights the importance of an ecological approach to plant selection and the integration of biodiversity conservation into urban greening strategies. By optimizing species choice based on functional traits, VGS can become more effective and sustainable tools for air pollution mitigation and urban resilience.