Nanoscale gas-water mixed ions for multifunctional air purification in built environments: a paradigm shift towards active air treatment

IAQ is challenged by infectious microorganisms, PM, and odorous compounds, requiring multifunctional mitigation strategies. GWMI are nanoscale water droplets, typically 5-30 nm in diameter, carrying surface charges and ROS, such as hydroxyl and superoxide radicals. Generated via high-voltage electrostatic atomisation of water, GWMI are mobile, relatively long-lived, and capable of actively interacting with airborne contaminants. This review systematically synthesises GWMI air purification in built environments, covering generation principles, physicochemical characteristics, functional mechanisms, application scenarios, influencing factors, and implementation challenges. The reviewed evidence shows that GWMI can suppress bacteria, viruses, and fungal spores, remove airborne PM through charge-mediated coagulation and deposition, and mitigate odours through ROS-driven oxidation. Reported studies show microbial reductions ranging from moderate suppression to >99% inactivation under controlled conditions, PM removal efficiencies of approximately 30-80% depending on particle size and device configuration, and substantial removal of representative odorous compounds, including nicotine, cooking-related volatiles, ammonia, and isovaleric acid. Performance is mainly governed by applied voltage, electrode spacing, needle number and arrangement, water supply mode, airflow pattern, RH, exposure duration, pollutant characteristics, and active additives. Mechanistically, GWMI act through ROS-induced oxidative damage, electrostatic interactions, aerosol coagulation, and enhanced pollutant-droplet contact. Compared with conventional and hybrid air-cleaning technologies, GWMI offer the potential for active, spatially distributed, and multifunctional treatment. However, current evidence remains limited by heterogeneous test conditions, insufficient standardised metrics, incomplete long-term safety data, possible O 3 generation at high voltages, and scalability challenges in large-volume spaces. By examining the remaining challenges for large-scale deployment and integration, this review outlines future prospects for GWMI as an emerging active air-cleaning paradigm in healthier built environments.