Air quality in care facilities: Possibly infectious particles

Abstract

This study investigates how air cleaning reduces airborne particle and bacterial concentrations in healthcare environments, aiming to lower infection risk without increasing mechanical ventilation rates. The study combines laboratory experiments, infection risk modelling, and field measurements in a hospital waiting room. Under laboratory conditions, the Clean Air Delivery Rate (CADR) of the electrostatic air cleaner was determined using particle concentration decay measurements, yielding an average value of approximately 400 l/s, depending on particle size. These results were used to estimate equivalent air change rates and to model infection risk using the Wells–Riley approach via the REHVA calculator. The modelling indicates that adding a single air cleaner with a CADR of 400 l/s can reduce the theoretical probability of airborne infection by approximately 75–80% compared to a baseline ventilation rate of 5 air changes per hour (ACH), outperforming an increase to 8 ACH. Field measurements in a waiting room at Karolinska Universitetssjukhuset confirmed that high-CADR air cleaning significantly reduces airborne particle concentrations (up to 60–70%) and bacterial levels (approximately 40–55%) under real operating conditions. However, bacterial reductions showed greater variability due to changes in occupancy and activity levels. The results also demonstrate that air cleaners provide substantial improvements in indoor air quality at relatively low energy consumption. The estimated annual energy use is significantly lower than that required to achieve equivalent ventilation rates. Measured ozone levels, a potential by-product of electrostatic air cleaning (used during the experiments) remained well below recommended limits, indicating safe operation. Noise levels increased moderately but remained within acceptable ranges for healthcare environments. Overall, the findings demonstrate that electrostatic air cleaning can serve as an effective and energy-efficient supplementary strategy alongside ventilation for reducing airborne contaminants and infection risk in healthcare facilities, particularly in spaces with high occupancy or limited ventilation capacity.