2024 No Effect of ventilation strategies and air purifiers on the children's exposure to airborne particles and gaseous pollutants in school gyms https://www.sciencedirect.com/science/article/abs/pii/S0048969719356682?via%3Dihub Pacitto, A. Europe Experimental Elementary (K-5) Ventilation rates Particulate Matter (PM) Black carbon Nitrogen Dioxide (NO2) School gym Air purifier Particle number concentration Black carbon Particulate matter (PM) Indoor air quality In two Barcelona school gyms, air purifiers significantly reduced indoor/outdoor particle ratios—up to 95% in smaller gyms with high air changes per hour (ACH). Manual airing reduced purifier effectiveness, especially at low ACH (6% reduction). 2020