Impact of vertical greenery system on indoor air quality: Case study in a Luxembourg administrative building

Vertical greenery systems (VGS) have become increasingly popular in indoor environments due to their aesthetic value and potential to improve air quality. However, their real impact on indoor air and occupant health remains under-documented, especially in operational public buildings. This case study assesses the effects of VGS on indoor air quality (IAQ) in a recently renovated administrative building in Luxembourg, where five VGS comprising both depolluting and ornamental plant species were installed across three floors. Over 46 weeks, concentrations of formaldehyde, volatile organic compounds (VOCs), and airborne mold spores were systematically monitored near the VGS and in reference locations without VGS, alongside environmental parameters and qualitative feedback from staff. Formaldehyde concentrations were consistently lower in areas equipped with VGS compared to reference sites, with reductions of up to 40% in separate zones. While the overall VOC burden remained similar with and without VGS, a significant decrease was observed in the concentration of aromatic compounds and ketones near VGS installed in confined or well-ventilated zones. However, the presence of VGS led to increased mold spore concentrations, particularly where high humidity or suboptimal maintenance favored fungal growth. No toxic or pathogenic molds were detected. The study demonstrates that VGS can contribute to lowering certain indoor air pollutants, primarily formaldehyde, yet underscores the importance of proper design and maintenance to control mold risks. Recommendations address irrigation, substrate hygiene, and system location for optimal IAQ and user acceptability.