Particulate matter (PM) exposure in urban areas is a continuous threat to human health and requires sustainable solutions for effective reduction. The aim of this study is to provide a comprehensive overview of façade greening and its effects on PM and to identify knowledge gaps. We systematically screened, analyzed, and re-evaluated previous reviews according to the criteria established for an umbrella review. As a result, this study covers and discusses common measurement methods, influencing factors, the effectiveness of façade greening, leaf characteristics, and plant species from different subtopics. The main findings are that inconsistent measurement methods limit the comparability of the analyzed reviews, and different climatic conditions affecting the use of plant species lead to different international effects. Despite the existing studies reporting a positive effect on the reduction of PM, comparability is difficult due to methodological differences and external influences. Given the complexity, interdisciplinary collaboration with experts is essential to increase the effectiveness of façade greening for PM accumulation for healthy urban air. We suggest that this umbrella review provides a foundation for future research and practical implementations, such as a suitable plant selection or façade design, by integrating the results.

Over the recent decades, technological advancements have led to a rise in the use of so-called technology-critical elements (TCEs). Environmental monitoring of TCEs forms the base to assess whether this leads to increased anthropogenic release and to public health implications. This study employs an exploratory approach to investigate the distribution of the TCEs Li, Be, V, Ga, Ge, Nb, Sb, Te, Ta, Tl, Bi and the REYs (rare-earth elements including yttrium) in urban aerosol in the city of Vienna, Austria. Leaf samples (n = 292) from 8 plant species and two green facades and water samples (n = 18) from the Wienfluss river were examined using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Surface dust contributions were assessed by washing one replicate of each leaf sample and analysing the washing water (n = 146). The impacts of sampling month, plant species and storey level on elemental distribution were assessed by statistical tools and generative deep neural network modelling. Higher TCE levels, including Li, V, Ga, Ge, Tl, Bi, and the REYs, were found in the winter months, likely due to the use of de-icing materials and fossil fuel combustion. A. millefolium and S. heufleriana displayed the highest levels of Li and Ge, respectively. In addition, increased elemental accumulation at lower storeys was observed, including Be, Sb, Bi and the REYs, indicating greater atmospheric dust deposition and recirculation closer to ground level. The results suggest a broad association of TCE levels with urban dust. This study enhances the current understanding of TCE distribution in urban settings and underscores the importance of their inclusion in pollution monitoring. It highlights the complex interplay of human activities, urban infrastructure, and environmental factors, offering valuable insights for managing urban environmental health risks and underlining the need for comprehensive urban ecosystem studies.

Ambient air pollutants are a global public health problem accounting for millions of annual deaths. A mobile module-based wind tunnel (WT) was developed to investigate the interaction between airborne particulate matter and various surface structures. The external dimensions were 4.33 m × 1.96 m × 1.73 m (lwh). The tunnel provided a cross-section of 0.40 m × 1.10 m (wh) and a total volume of 2.84 m³. An exchangeable test section in the WT offered a vertical area of one square meter to introduce variable installations. Due to the modular design, the WT could be divided into seven segments. This enables flexibility in setting, easy transport and set up at different locations. Atmospheric parameters (temperature, humidity, flow speeds and flow directions) were measured. At the test section, determined flow speeds ranged from 0.3 to 2.6 m s⁻¹, with turbulence intensities detected between 9% and 11% and Reynold numbers from 10,000 to 90,000. Losses of ambient PM within the blank tunnel were less than 10% for particle counts (>0.25 µm), while smaller losses were obtained for PM₁ and PM_2.5. Thus, the construction, performance, as well as the limitations and various possible applications of the WT are shown in this article.