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The utilization of physical dividers has been recommended as a practical approach to reducing the droplet and aerosol transmissions of the COVID-19 virus (SARS-CoV-2). This study conducted a series of experiments using video recording with a high-speed camera, particle image velocimetry (PIV) technique, and concentration measurements. The effectiveness of Perspex desk dividers impeding the transient transmission during coughing in five representative layouts was investigated. The results showed that the divider effectively protected the exposed person from an infector's cough seated in a face-to-face arrangement at a distance of 1.5 m. The aerosol concentration at the breathing zone was reduced by 99% compared to the layout without dividers. However, the reflection of aerosols from the dividers increased the exposure risk to the person seated beside the infector. Such risk was substantially reduced if the dividers were placed parallel between the infector and exposed person seated side-by-side. When the exposed person was staggered (face-to-face but displaced sideways laterally) to the infector with a 0.55-m lateral distance, the dividers reduced the potential exposure at the breathing zone by 60%. Considering the effectiveness in exposure reduction, the staggered configuration of desk dividers between the infector and exposed persons offers the best reduction to exposure., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

In a business as usual scenario, atmospheric carbon dioxide concentration (CO 2 ) could reach 950 parts per million (ppm) by 2100. Indoor CO 2 concentrations will rise consequently, given its dependence on atmospheric CO 2 levels. If buildings are ventilated following current standards in 2100, indoor CO 2 concentration could be over 1300 ppm, depending on specific ventilation codes. Such exposure to CO 2 could have physiological and psychological effects on building occupants. We conducted a randomized, within-subject study, examining the physiological effects on the respiratory functions of 15 persons. We examined three exposures, each 150 min long, with CO 2 of: 900 ppm (reference), 1450 ppm (decreased ventilation), and 1450 ppm (reference condition with added pure CO 2 ). We measured respiratory parameters with capnometry and forced vital capacity (FVC) tests. End-tidal CO 2 and respiration rates did not significantly differ across the three exposures. Parameters measured using FVC decreased significantly from the start to the end of exposure only at the reduced ventilation condition (p < 0.04, large effect size). Hence, poor ventilation likely affects respiratory parameters. This effect is probably not caused by increased CO 2 alone and rather by other pollutants-predominantly human bioeffluents in this work-whose concentrations increased as a result., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The performance of a low-cost fan filter unit (FFU) in mitigating hazardous particulate matter (PM) levels in a naturally ventilated school classroom is presented. The FFU can be considered as a simplified mechanical ventilation and air-conditioning system without heating and cooling functions. The FFU improves indoor air quality through introduction of cleaned outdoor air to flush out internally generated heat and moisture and reducing infiltration by maintaining indoor pressurization. Indoor particle number concentrations were reduced between 85% and 95%. The particle removal performance (PRF FFU ) of the FFU is determined and incorporated into the augmented façade penetration factor (P aug ). A case-specific recursive dynamic mass balance model is used to characterize the infiltration factor (F INF ), deposition rate (K), and the penetration efficiency (P aug ) from continuously monitored indoor and outdoor mass concentration levels. Computed "P aug " (0.07, 0.09, and 0.13) and "F INF " (0.06, 0.08, and 0.11), respectively, for PM10, PM2.5, and PM1 suggest that exposure to PM was significantly reduced indoors. The effectiveness of the FFU for reduced "F INF " and "P aug " may be attributed to its superior filtration, dilution, and exfiltration mechanisms. In comparison with alternative PM mitigation solutions, the FFU is effective, affordable, and sustainable., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Singapore is a tropical country with a high density of day-care facilities whose indoor environments may be adversely affected by outdoor fine particle (PM 2.5 ) air pollution. To reduce this problem requires effective, evidence-based exposure-reduction strategies. Little information is available on the penetration of outdoor PM 2.5 into day-care environments. Our study attempted to address the following objectives: to measure indoor infiltration factor (F inf ) of PM 2.5 from outdoor PM 2.5 and to determine the building parameters that modify the indoor PM 2.5 . We collected indoor/outdoor 1-min PM 2.5 from 50 day-care classrooms. We noted mean F inf  ± SD of 0.65 ± 0.22 in day-care rooms which are naturally ventilated and lower F inf  ± SD values of 0.47 ± 0.18 for those that are air-conditioned: values which are lower than those reported in Singapore residences. The air exchange rates were higher in naturally ventilated rooms (1.47 vs 0.86 h -1 ). However, fine particle deposition rates were lower for naturally ventilated rooms (0.67 ± 0.43 h -1 ) compared with air-conditioned ones (1.03 ± 0.55 h -1 ) presumably due to composite rates linked to the filters within the split unit air-conditioners, higher recirculation rates, and interior surfaces in the latter. Our findings indicate that children remaining indoor in daycares where air-conditioning is used can reduce their PM 2.5 exposures during outdoor pollution episodes., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

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 were 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 × 10 6 #/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., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

To date, exposure studies linking dust-mite allergens with asthma and allergic morbidities have typically relied on sampling from representative locations in the home for exposure assessment. We determine the effects of differing microenvironments allergen exposures on asthma and asthma severity among 25 case and 31 control preschool children in Singapore. Blo t 5 allergen levels in various niches from the children's home and day-care microenvironments as well as their Blo t 5 time-weighted concentrations were determined. Eosinophilic cationic protein (ECP) levels from the children's saliva as markers for airway inflammation were obtained. Salivary ECP levels were higher in children with asthma than those without and the strength of association increased with higher salivary ECP levels. Although there was no relationship between time-weighted Blo t 5 concentrations with salivary ECP levels among the controls, a positive statistically significant relationship was noted among cases, demonstrating the effects of cumulative exposure on asthma severity. Avoidance measures to reduce Blo t 5 allergen exposure should include all microenvironments that asthmatic children are exposed throughout the day., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Indoor environmental quality (IEQ) has become an important component of green building certification schemes. While green buildings are expected to provide enhanced IEQ, higher occupant satisfaction, and less risks of occupant health when compared with non-green buildings, the literature suggests inconsistent evidence due to diverse research design, small sample size, and weak statistical analysis. This study compared several outcomes pertinent to IEQ performance in green and non-green office buildings in Singapore. Adopting a cross-sectional study design, objective measurements were taken in eight green and six non-green buildings, and satisfaction and acute health symptom risks of 367 occupants were obtained. Green buildings exhibited lower concentration of PM2.5, bacteria, and fungi and maintained temperature and humidity more consistently compared to non-green counterparts. The mean ratings for satisfaction with temperature, humidity, lighting level, air quality, and indoor environment were higher in green buildings (with statistical significance P < 0.05). There was statistically significant reduction in risk of occupants having headache, unusual fatigue, and irritated skin in green buildings. Although matching of buildings and occupant characteristics, survey participation bias, and sampling duration (a 1-week snapshot) of IEQ monitoring remain as limitations, this study offered positive association of green buildings with qualitatively and quantitatively measured performance of IEQ., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Unlabelled: The effects of the human convective boundary layer (CBL), room airflow patterns, and their velocities on personal exposure are examined. Two pollutants are studied which simulate particles released from the feet and generated at distances of 2 and 3 m by a human cough. A thermal manikin whose body shape, size, and surface temperatures correspond to those of an average person is used to simulate the CBL. The findings of the study reveal that for accurate predictions of personal exposure, the CBL needs to be considered, as it can transport the pollution around the human body. The best way to control and reduce personal exposure when the pollution originates at the feet is to employ transverse flow from in front and from the side, relative to the exposed occupant. The flow from the above opposing the CBL create the most unfavorable velocity field that can increase personal exposure by 85%, which demonstrates a nonlinear dependence between the supplied flow rate and personal exposure. In the current ventilation design, it is commonly accepted that an increased amount of air supplied to the rooms reduces the exposure. The results of this study suggest that the understanding of air patterns should be prioritized., Practical Implications: A human convective boundary layer plays an important role in pollution transport around the human body. It interacts with the surrounding airflows which modifies air movement around the human body and personal exposure. Understanding the influence of this interaction on the pollution spread around the human can be used to control and reduce personal exposure and improve HVAC design., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Unlabelled: The inhalation intake fraction was used as an indicator to compare effects of desktop personalized ventilation and mixing ventilation on personal exposure to directly released simulated cough droplets. A cough machine was used to simulate cough release from the front, back, and side of a thermal manikin at distances between 1 and 4 m. Cough droplet concentration was measured with an aerosol spectrometer in the breathing zone of a thermal manikin. Particle image velocimetry was used to characterize the velocity field in the breathing zone. Desktop personalized ventilation substantially reduced the inhalation intake fraction compared to mixing ventilation for all investigated distances and orientations of the cough release. The results point out that the orientation between the cough source and the breathing zone of the exposed occupant is an important factor that substantially influences exposure. Exposure to cough droplets was reduced with increasing distance between cough source and exposed occupant., Practical Implications: The results from this study show that an advanced air distribution system such as personalized ventilation reduces exposure to cough-released droplets better than commonly applied overhead mixing ventilation. This work can inform HVAC engineers about different aspects of air distribution systems’ performance and can serve as an aid in making critical design decisions., (© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The impact of asthma, exposure period, and filter condition downstream of the mixing box of air-conditioning system on building occupants' perceptual response, work performance, and salivary α-amylase secretion during exposures to ozone and its initiated chemistry products is studied. The experiments were conducted in a field environmental chamber (FEC) (240 m(3)) simulating an office environment. Experiments were conducted during periods when the air-handling system operated with new or used pleated panel filters at constant recirculation (7/h) and ventilation (1/h) rates. Average ozone and secondary organic aerosols (ozone-initiated chemistry products) measured during non-asthmatic and asthmatic subjects' 3-h exposures in the FEC were in the ranges approximately 20-37 ppb and approximately 1.6-3 μg/m(3), respectively. Asthmatic subjects' perceived odor intensity and sensory (eye, nose, and throat) irritation ratings were generally lower than those of non-asthmatic subjects, possibly explaining why asthmatic subjects accept perceived air quality more than non-asthmatic subjects. However, asthmatic subjects' perceived physiological-like symptom ratings (flu, chest tightness, and headache) and concentrations of secreted salivary α-amylase were generally higher than those of non-asthmatic subjects. Asthmatic subjects had significantly lower accuracy than non-asthmatic subjects in a task that required higher concentration although they had higher work speed. Filter condition did not make any significant difference for subjects' responses., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

This study investigates the interaction between the human convective boundary layer (CBL) and uniform airflow with different velocity and from different directions. Human body is resembled by a thermal manikin with complex body shape and surface temperature distribution as the skin temperature of an average person. Particle image velocimetry (PIV) and pseudocolor visualization (PCV) are applied to identify the flow around the manikin's body. The findings show that the direction and magnitude of the surrounding airflows considerably influence the airflow distribution around the human body. Downward flow with velocity of 0.175 m/s does not influence the convective flow in the breathing zone, while flow at 0.30 m/s collides with the CBL at the nose level reducing the peak velocity from 0.185 to 0.10 m/s. Transverse horizontal flow disturbs the CBL at the breathing zone even at 0.175 m/s. A sitting manikin exposed to airflow from below with velocity of 0.30 and 0.425 m/s assisting the CBL reduces the peak velocity in the breathing zone and changes the flow pattern around the body, compared to the assisting flow of 0.175 m/s or quiescent conditions. In this case, the airflow interaction is strongly affected by the presence of the chair., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Unlabelled: This paper reports the effects of ventilation strategies on indoor air quality (IAQ) and respiratory health of children within 104 child care centers (CCCs) in a hot and humid climate. The CCCs were categorized by ventilation strategies: natural (NV), air-conditioned and mechanically ventilated (ACMV), air-conditioned using split units (AC), and hybrid (NV and AC operated intermittently). The concentration levels of IAQ parameters in NV CCCs are characterized by the influence of the outdoors and good dilution of indoor pollutants. The lower ventilation rates in air-conditioned CCCs result in higher concentrations of occupant-related pollutants but lower outdoor pollutant ingress. This study also revealed lower prevalence for most asthma and allergy, and respiratory symptoms in children attending NV CCCs. In multivariate analyses controlled for the effects of confounders, the risk of current rhinitis among children is significantly higher if they attend mechanically ventilated CCCs compared to NV CCCs. Air-conditioned CCCs were also associated with higher adjusted prevalence ratio of severe phlegm and cough symptoms and lower respiratory illness. Finally, children attending CCCs with hybrid ventilation are at high risk for almost all the respiratory symptoms studied., Practical Implications: This large field study indicates that different ventilation strategies employed by child care centers can cause significant variations in the indoor air quality and prevalence of asthma, allergies and respiratory symptoms of attending children. The higher prevalence rates of allergic and respiratory symptoms among young children, whose immune system is still under-developed, in child care centers, whether fully or partially air-conditioned, suggest that ventilation and plausible growth and propagation mechanisms of allergens and infectious agents be further investigated.

Unlabelled: An attempt was made to determine the relationship between airborne viable bacteria (predominantly of human origin) and particle concentrations of different sizes in a controlled environmental chamber focusing on the effect of temperature setting. At temperature settings of 20 degrees and 26 degrees C, six subjects performed simulated office work for 2.5 h, and the particle and total bacteria concentrations at six aerodynamically corresponding size ranges were measured at 20-min intervals. The study revealed that the main contributor of viable bacteria was humans. Viable bacteria concentrations in the size range between 1 and 3 microm was higher at 20 degrees C than at 26 degrees C. Bacteria >7.5 microm showed good correlation with particles of similar minimum size, and it is postulated that this may be because of bacteria rafting on skin scales shed by the subjects. At sizes between 3 and 7.5 microm, the correlations indicated that bacteria exists as clumps, while at size ranges between 1.0 and 2 microm bacteria exists freely. At 26 degrees C, bacteria of size >7.5 microm correlated with exhaled carbon dioxide indicating nasal carriers. Viability of bacteria was shown to be affected by thermal effects. The percentages of particles that were viable bacteria at the different sizes were all found to be very low (<1%)., Practical Implications: Due to their respiratory health effects, determining exposure to airborne viable bacteria and particles of different sizes requires the study of their behavior in relation to each other. This study attempts to characterize the relationships of bacteria and particles that are predominantly of human origin. Findings of this work will help researchers in understanding how bacteria levels co-exist with particles of corresponding aerodynamic size across different size ranges between 20 degrees and 26 degrees C.

Unlabelled: A study was performed in a call center that provides billing inquiry services using a 2 x 2 balanced experimental plan for nine consecutive weeks. Two independent variables, temperature and outdoor air supply rate, were combined and introduced to the occupants in a blind intervention approach. The temperature set-points were fixed at 22.5 degrees C and 24.5 degrees C, and outdoor air supply rate at 5 l /s/p and 10 l/s/p. Temperature and outdoor air supply rate had significant interaction effects on worker's talk time (P < 0.001), which means that the effects of temperature on talk time performance were not independent of the effects of outdoor air supply rate or the opposite. Talk time was reduced significantly when the outdoor air supply rate was increased from 5 l /s/p to 10 l/s/p at 24.5 degrees C (P < 0.01); this may be associated with the significant reduction in a principal component factor which includes intensity of dryness, aching eyes and nose-related symptoms (P < 0.01). Decreasing the temperature from 24.5 degrees C to 22.5 degrees C at 10 l /s/p significantly increased talk time (P < 0.01). Analysis of the principal component factor based on the neurobehavioral symptoms also revealed that temperature reduction led to an increased mean factor score of these symptoms (P < 0.04)., Practical Implications: For moderately complex office work which involves manipulation dexterity such as a call center operation where call operators interact with computer-based information systems, tropically acclimatized workers' performance could be improved by increasing the outdoor air supply rate from 5 l/s/p to 10 l/s/p if the temperature is to be maintained at the higher band of the thermal comfort range, around 24.5 degrees C. At a low ventilation rate (5 l/s/p), decreasing the temperature from 24.5 degrees C to 22.5 degrees C (which is a commonly adopted set-point in tropical office buildings) also leads to improvement of talk time performance. The magnitude of talk time improvement was greater by more than four times when the strategy to increase the outdoor air supply rate was implemented at a lower range of outdoor air supply rate (5-10 l /s/p) as compared to the higher range (9.8-22.7 l/s/p).

An integrated indoor air quality (IAQ)-energy audit methodology has been developed in this study in Singapore, which provides a rigorous and systematic method of obtaining the status-quo assessment of an 'IAQ signature' in a building. The methodology entails a multi-disciplinary model in obtaining measured data pertaining to different dimensions within the built environment such as the physical, chemical, biological, ventilation, and occupant response characteristics. This paper describes the audit methodology and presents the findings from five air-conditioned office buildings in Singapore. The research has also led to the development of an indoor pollutant standard index (IPSI), which is discussed in this paper. Other performance indicators such as, the ventilation index and the energy index as well as the building symptom index (BSI) are also presented and discussed in the context of an integrated approach to IAQ and energy. Several correlation attempts were made on the various symptoms, indoor air acceptability, thermal comfort, BSI and IPSI, and while BSI values are found to correlate among them as well as with IAQ and THERMAL COMFORT acceptability, no such correlation was observed between BSI and IPSI. This would suggest that the occupants' perception of symptoms experienced as well as environmental acceptability is quite distinct from IAQ acceptability determined from empirical measurements of indoor pollutants, which reinforces the complex nature of IAQ issues.

The impact of electrostatic precipitation as a useful form of particulate filtration in the breathing zone is investigated in an intervention study in an air-conditioned commercial office in central London. Surface dust deposition and airborne dust levels are measured in the open plan zones of two floors--a control floor and a floor where the intervention is effected. The intervention consists of a sequence of weekly scenarios where the main pre-filters of the air-handling unit are switched between new and old filters, and where the electrostatic filters, located as uniformly as practicable on the open plan areas, are switched on or off. This 2 x 2 set of interventions is repeated over 4 cycles. It was found that the breathing zone filtration (BZF) by electrostatic precipitators reduces airborne dust significantly and appears to be more efficient in reducing smaller sized particles. No significant effect of BZF filters in reducing surface dust deposition was detected.