Enhancing Indoor Environmental Quality in Hot and Arid Climates: Experimental Evaluation of Plant-Based Air Purification and Microclimate Stabilization in Riyadh

In hot-arid urban environments such as Riyadh, Saudi Arabia, indoor air quality (IAQ) has emerged as a critical public health issue due to the widespread use of airtight residential buildings and reliance on mechanical ventilation. This study investigates the effectiveness of indoor vegetation in improving indoor environmental quality (IEQ) by reducing formaldehyde (HCHO) concentrations and stabilizing thermal and humidity conditions. Full-scale laboratory experiments were conducted in simulated apartment units configured to reflect standard Riyadh construction practices. Across three experimental phases—baseline (no vegetation), plant placement, and plant placement with mechanical ventilation—HCHO, temperature, and humidity were continuously monitored for 5 days. The results indicate that indoor plants significantly reduced HCHO concentrations in vegetated zones (by 0.312 ppm on average) compared to control zones, while also moderating temperature fluctuations and maintaining humidity between 75 and 87%. Introducing mechanical air circulation between zones extended the benefits to adjacent living spaces, demonstrating that even passive or forced airflow can enhance the spatial effectiveness of plant-based purification strategies. In contrast, non-vegetated zones maintained high HCHO levels and exhibited greater environmental instability. These findings highlight the synergistic potential of combining biophilic design with low-energy mechanical systems to achieve healthier indoor environments. The study provides empirical evidence for integrating vegetation into residential design strategies aligned with Vision 2030 and the Saudi Green Initiative. It also underscores the need for long-term IAQ monitoring and construction quality controls to optimize occupant health and building sustainability in the Gulf region.