Characterization of expiration air jets and droplet size distributions immediately at the mouth opening.

Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The average expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the experimental setting, evaporation and condensation effects had negligible impact on the measured droplet size. The geometric mean diameter of droplets from coughing was 13.5 µm and it was 16.0 µm for speaking (counting 1-100). The estimated total number of droplets expelled ranged from 947 to 2085 per cough and 112-6720 for speaking. The estimated droplet concentrations for coughing ranged from 2.4 to 5.2 cm-3 per cough and 0.004-0.223 cm-3 for speaking.

A methodology for estimating airborne virus exposures in indoor environments using the spatial distribution of expiratory aerosols and virus viability characteristics.

UNLABELLED: This study investigated the feasibility of using the spatial distribution of expiratory aerosols and the viability functions of airborne viruses to estimate exposures to airborne viruses in an indoor environment under imperfectly mixed condition. A method adopting this approach was tested in an air-conditioned hospital ward. Artificial coughs were produced by aerosolizing a simulated respiratory fluid containing a known concentration of benign bacteriophage. The bacteriophage exposures estimated on the basis of the spatial aerosol distributions and its viability function were in reasonable agreement with those measured directly by biological air sampling and culturing. The ventilation flow and coughing orientation were found to play significant roles in aerosol transport, leading to different spatial distribution patterns in bacteriophage exposure. Bacteriophage exposures decreased with lateral distance from the infector when the infector coughed vertically upward. In contrast, exposures were constant or even increased with distance in the case of lateral coughing. The possibility of incorporating the proposed exposure estimation into a dose-response model for infection risk assessment was discussed. The study has also demonstrated the potential application of viability functions of airborne viral pathogens in exposure assessment and infection risk analysis, which are often unavailable in literature for some important communicable diseases. PRACTICAL IMPLICATIONS: The proposed method makes use of the viability function of the virus and the spatial distribution of the expiratory aerosols for virus exposure estimation. Spatial differences in aerosol distribution and its influences on virus exposure in an air space can be determined. Variations in infectious dose with carrier aerosol size could also be considered. The proposed method may serve as a tool for further investigation of ventilation design and infection control in clinical or other indoor environments.

Catalytic ozonation of toluene using zeolite and MCM-41 materials.

The effects of passing ozone over different zeolite and MCM-41 materials to remove toluene were investigated. Different ozone-to-toluene ratios were used to evaluate the catalytic performance during ozonation. The micro- and meso-porous materials removed about 50% of the toluene via adsorption and another 20-40% was decomposed by ozonation, which was catalytically enhanced by the zeolite and MCM-41 materials. The catalytic reaction portion increased by using a higher ozone inlet concentration and it was further enhanced to around 50% with the use of more adsorbents or with longer residence times. Inside the porous structure of the material, ozone was either decomposed into active atomic oxygen for reactions or converted into oxygen for active site regeneration. The number of Lewis acid sites in the adsorbents for ozone decomposition and byproduct generation during the reactions limit the catalytic activities. Trace amounts of intermediates including aldehydes and organic acids were quantified in the ozonation process. A higher ozone inlet concentration helped to reduce intermediate species formation but it led to more residual ozone in the exhaust. The high adsorption capability of the zeolite and MCM-41 adsorbents could serve as reservoirs for suppressing the release of intermediate species to the exhaust.

Transport characteristics of expiratory droplets and droplet nuclei in indoor environments with different ventilation airflow patterns.

Expiratory droplets and droplet nuclei can be pathogen carriers for airborne diseases. Their transport characteristics were studied in detail in two idealized floor-supply-type ventilation flow patterns: Unidirectional-upward and single-side-floor, using a multiphase numerical model. The model was validated by running interferometric Mie imaging experiments using test droplets with nonvolatile content, which formed droplet nuclei, ultimately, in a class-100 clean-room chamber. By comparing the droplet dispersion and removal characteristics with data of two other ceiling-supply ventilation systems collected from a previous work, deviations from the perfectly mixed ventilation condition were found to exist in various cases to different extent. The unidirectional-upward system was found to be more efficient in removing the smallest droplet nuclei (formed from 1.5 mum droplets) by air extraction, but it became less effective for larger droplets and droplet nuclei. Instead, the single-side-floor system was shown to be more favorable in removing these large droplets and droplet nuclei. In the single-side-floor system, the lateral overall dispersion coefficients for the small droplets and nuclei (initial size

A study of the dispersion of expiratory aerosols in unidirectional downward and ceiling-return type airflows using a multiphase approach.

Dispersion characteristics of expiratory aerosols were investigated in an enclosure with two different idealized airflow patterns: the ceiling-return and the unidirectional downward. A multiphase numerical model, which was able to capture the polydispersity and evaporation features of the aerosols, was adopted. Experiments employing optical techniques were conducted in a chamber with downward airflow pattern to measure the dispersion of aerosols. Some of the numerical results were compared with the chamber measurement results. Reasonable agreement was found. Small aerosols (initial size

Numerical and experimental study of velocity and temperature characteristics in a ventilated enclosure with underfloor ventilation systems.

UNLABELLED: Airflow and temperature distributions in an enclosure with heat sources ventilated by floor supply jets with floor or ceiling air exit vents were investigated using experimental and numerical approaches. These ventilation configurations represent the floor return or the top return underfloor ventilation systems found in real applications. Experiments and numerical simulations were performed on a full-sized environmental chamber. The results reveal that the temperature stratification in the enclosure highly depended on the thermal length scale of the floor supply jets. When the thermal length scale of the supply jet was >>1, temperature stratification was minor for all tested heat densities and air distribution methods. Significant vertical temperature gradients occurred when the jet thermal length scale was <<1. Changes in air distribution methods also became significant for temperature stratification at small supply jet thermal length scales. Temperature stratification also affected the terminal height of the momentum-dominant region of the vertical buoyant supply jets. The applicability of these results to underfloor ventilation design was also discussed. PRACTICAL IMPLICATIONS: In designing underfloor ventilation systems, supply jet conditions and heat load density have to be considered to avoid thermal discomfort because of excessive temperature stratifications. This study demonstrated, by both numerical simulations and experiments, that thermal length scale can be used as a design indicator to predict thermal stratifications under a floor return and a top return underfloor ventilation setting.

Experimental study of ventilation performance and contaminant distribution of underfloor ventilation systems vs. traditional ceiling-based ventilation system.

UNLABELLED: Ventilation performance and pollutant distribution in a traditional ceiling-type ventilation system, a top-return (TR)-type and a floor-return (FR)-type underfloor ventilation systems were performed in a controlled experimental room. Tracer gas method was utilized to determine the age of air and the contaminant removal effectiveness. Tobacco smoke was also introduced to study the particle-phase pollutant distribution. The TR system delivered conditioned air more efficiently in the occupied zone and exhibited higher gaseous contaminant removal effectiveness. It also showed the lowest smoke particle concentration compared with the other two systems. The FR system showed better ventilation performance over the mixing system at the space that was close to the floor supply outlet and at the lower height level. The FR system was less effective than the TR system in removing buoyant tobacco smoke particles at the upper part of the room indicating its highly localized characteristics. Differences in experimental conditions between the present and the previous studies and their effects on the experimental results are discussed. In general, the experimental data suggested that both types of the underfloor ventilation systems have the potential of improving air quality at the breathing zone over the ceiling-based mixing system with suitable designs. PRACTICAL IMPLICATIONS: This study shows the possibility of improving indoor air quality using underfloor ventilation systems compared with the traditional ceiling-based ventilation system. However, different configurations of the underfloor ventilation system show various ventilation characteristics. The engineers should consider these features when implementing an underfloor ventilation design. The top-return (TR) configuration improves indoor air quality by creating a displacement-like flow pattern while the floor-return (FR) configuration shows highly localized ventilation characteristics. The FR configuration improved the indoor air quality at spaces near the floor diffusers and up to certain heights.

A study on the prevalence of and risk factors for neck pain among university academic staff in Hong Kong.

The 1-year prevalence of neck pain and possible risk factors among university academic staff were investigated. Self-administered questionnaires were distributed to all the full-time academic staff in one of the universities in Hong Kong. The 1-year prevalence of neck pain was investigated. The relationship between individual factors, job nature, psychosocial factors, and neck pain were also analyzed. The 1-year prevalence of neck pain among after being an academic staff was 46.7%. A significant association was found between gender and neck pain (p = 0.02). The percentage of female academic staff with neck pain (62%) was higher than that in male staff (38%). This matched the results of other studies, which demonstrated that neck pain was more prevalent in women. There was a significant association between head posture during computer processing and neck pain (p = 0.02). Among those with neck pain during computer processing, 60.5% had a forward head posture. However, a low correlation between psychosocial factors and neck pain was demonstrated (r = 0.343). Academic staff in tertiary institutions could be considered as a high-risk group of job-related neck pain.