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Indoor air, especially with suspended particulate matter (PM), can be a carrier of airborne infectious pathogens. Without sufficient ventilation, airborne infectious diseases can be transmitted from one person to another. Indoor air quality (IAQ) significantly impacts people's daily lives as people spend 90% of their time indoors. An industrial-grade air cleaner prototype (filtration + ultraviolet light) was previously upgraded to clean indoor air to improve IAQ on two metrics: particulate matter (PM) and viable airborne bacteria. Previous experiments were conducted to test its removal efficiency on PM and airborne bacteria between the inlet and treated air. However, the longer-term improvement on IAQ would be more informative. Therefore, this research focused on quantifying longer-term improvement in a testing environment (poultry facility) loaded with high and variable PM and airborne bacteria concentrations. A 25-day experiment was conducted to treat indoor air using an air cleaner prototype with intermittent ON and OFF days in which PM and viable airborne bacteria were measured to quantify the treatment effect. The results showed an average of 55% reduction of total suspended particulate (TSP) concentration between OFF days (110 μg/m 3 ) and ON days (49 μg/m 3 ). An average of 47% reduction of total airborne viable bacteria concentrations was achieved between OFF days (∼3200 CFU/m 3 ) and ON days (∼2000 CFU/m 3 ). A cross-validation (CV) model was established to predict PM concentrations with five input variables, including the status of the air cleaner, time (h), ambient temperature, indoor relative humidity, and day of the week to help simulate the air-cleaning effect of this prototype. The model can approximately predict the air quality trend, and future improvements may be made to improve its accuracy., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Jacek Koziel reports financial support was provided by Kryton Engineered Metals Inc. and the Center for Industrial Research and Service (CIRAS) at Iowa State University., (Published by Elsevier Ltd.)

Since the COVID-19 pandemic, improving indoor air quality (IAQ) has become vital for the public as COVID-19 and other infectious diseases can transmit via inhalable aerosols. Air cleaning devices with filtration and targeted pollutant treatment capabilities can help improve IAQ. However, only a few filtration/UV devices have been formally tested for their effectiveness, and little data is publicly available and UV doses comparable. In this research, we upgraded a particulate matter (PM) air filtration prototype by adding UV-C (germicidal) light. We developed realistic UV dose metrics for fast-moving air and selected performance scenarios to quantify the mitigation effect on viable airborne bacteria and PM. The targeted PM included total suspended particulate (TSP) and a coarse-to-fine range sized at PM 10 , PM 4 , PM 2.5 , and PM 1 . The PM and viable airborne bacteria concentrations were compared between the inlet and outlet of the prototype at 0.5 and 1.0 m 3 /s (low and high) air flow modes. The upgraded prototype inactivated nearly 100% of viable airborne bacteria and removed up to 97% of TSP, 91% of PM 10 , 87% of PM 4 , 87% of PM 2.5 , and 88% of PM 1 . The performance in the low flow rate mode was generally better than in the high flow rate mode. The combination of filtration and UV-C treatment provided 'double-barrier' assurance for air purification and lowered the risk of spreading infectious micro-organisms.