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Research on triethylene glycol (TEG) use to disinfect airborne microorganisms have been conducted in non-realistic chamber settings. This study assesses how air temperature, humidity, HVAC settings, and filtration impact TEG's effectiveness in deactivating a common SARS-CoV-2 substitute, MS2 bacteriophage, in a simulated non-occupied office-sized chamber. The chamber was served by a dedicated HVAC system operating at 22.0, 23.5 and 25.0 °C, at 40, 55 and 70 % relative humidity, at 0, 3 and 6 air change per hour (ACH) recirculation, at 0.8, 2.5 and 5.0 ACH outdoor ventilation and at no, MERV8 and MERV14 filtration status. Airborne MS2 log10 reductions in the presence of TEG increased linearly over time and we noted a higher MS2 inactivation rate with higher TEG concentration. The estimated TEG concentration needed for a one-log inactivation of the MS2 within an hour was 0.44 mg/m3. The efficacy of TEG declined with the increase in temperature from 22.0 to 25.0 °C, peaked at 55 % RH, increased with higher recirculation rates but decreased with increasing ventilation rates and higher efficiency filters. The results of our study suggest that the optimum environmental and building conditions for TEG performance is at 22.0 or 23.5 °C air temperature, 55 % relative humidity, 0.8 ACH ventilation rate and 6 ACH recirculation rate. By conducting experiments in simulated office conditions, this study closes significant knowledge gaps in TEG performance application.

We evaluated diurnal trends of size-resolved indoor and outdoor fluorescent biological airborne particles (FBAPs) and their contributions to particulate matter (PM) within 0.5-20 μm. After a ten-week continuous sampling via two identical wideband integrated bioaerosol sensors, we found that both indoor and outdoor diurnal trends of PM were driven by its bioaerosol component. Outdoors, the median [interquartile range] FBAP mass concentration peaked at 8.2 [5.8-9.9] μg/m3 around sunrise and showed a downtrend from 6:00 to 18:00 during the daytime and an uptrend during the night. The nighttime FBAP level was 1.8 [1.4-2.2] times higher than that during the daytime, and FBAPs accounted for 45 % and 56 % of PM during daytime and nighttime, respectively. Indoors, the rise in concentrations of FBAPs smaller than 1 μm coincided with the starting operation of the heating, ventilation, and air conditioning (HVAC) system at 6:00, and the concentration peaked at 8:00 and dropped to the daily average by noontime. This indicated that the starting operation of the HVAC system dislodged the overnight settled and accumulated fine bioaerosols into the indoor environment. For particles larger than 1 μm, the variation of mass concentration was driven by occupancy. Based on regression modeling, the contributions of indoor PM, non-FBAP, and FBAP sources to indoor mass concentrations were estimated to be 93 %, 67 %, and 97 % during the occupied period.

This study evaluated the interrelations between indoor and outdoor bioaerosols in a bedroom under a living condition. Two wideband integrated bioaerosol sensors were utilized to measure indoor and outdoor particulate matter (PM) and fluorescent biological airborne particles (FBAPs), which were within a size range of 0.5-20 μm. Throughout this one-month case study, the median proportion of FBAPs in PM by number was 19% (5%; the interquartile range, hereafter) and 17% (3%) for indoors and outdoors, respectively, and those by mass were 78% (12%) and 55% (9%). According to the size-resolved data, FBAPs dominated above 2 and 3.5 μm indoors and outdoors, respectively. Comparing indoor upon outdoor ratios among occupancy and window conditions, the indoor FBAPs larger than 3.16 μm was dominated by indoor sources, while non-FBAPs were mainly from outdoors. The occupant dominated the indoor source of both FBAPs and non-FBAPs. Under awake and asleep, count- and mass-based mean emission rates were 45.9 and 18.7 × 106 #/h and 5.02 and 2.83 mg/h, respectively. Based on indoor activities and local outdoor air quality in Singapore, this study recommended opening the window when awake and closing it during sleep to lower indoor bioaerosol exposure.