Efficacy of ambulance air purifiers with different photocatalytic oxidation components in the removal of Bacillus subtilis spores

Abstract Ambulances are enclosed environments that carry a high risk of airborne and surface microbial transmission, yet effective disinfection technologies remain limited. This study evaluated four photocatalytic oxidation (PCO) configurations—O₃+UVA + TiO₂, UVA + TiO₂, O₃+UVC + ZnO, and UVC + ZnO—against B. subtilis spores. The testing employed a prototype air purification system for ambulance applications, where the photocatalyst TiO 2 or ZnO was integrated into a filter medium. This system operated in combination with its corresponding UV light source (UVA or UVC) and an optional ozone generator; all housed within a laboratory-simulated ambulance cabin. (8.998 m³), where spores at 1.5 × 10⁸ CFU/mL (8 mL) were spray misted using a nebulizer and sampled using an Andersen Impactor, following the NIOSH method. Disinfection efficacy was quantified as the percentage reduction of B. subtilis spores in the air and on surfaces. Among the tested systems, efficacy ranked as UVA + TiO₂ > O₃+UVA + TiO₂ > O₃+UVC + ZnO > UVC + ZnO. UVA + TIO 2 achieved the most rapid and stable disinfection among the tested systems under controlled conditions, reducing airborne spores by > 80% within 15 min, achieving complete removal within 90 min, and reducing surface contamination by 96.77% at 120 min. In contrast, ZnO- and UVC-based systems exhibited lower or inconsistent performance. These findings identify UVA + TiO₂ photocatalysis as a safe, ozone-free, and highly effective strategy for ambulance air purification. Its rapid and durable antimicrobial action demonstrates clear advantages over approaches based on ozone or UVC, offering practical benefits for infection control in emergency medical services and providing a foundation for further optimization of photocatalytic technologies in healthcare settings.