Simulation of vertical dispersion and pollution impact of artificial light at night in urban environment.

The use of artificial light at night (ALAN) enables social and commercial activities for urban living. However, the excessive usage of lighting causes nuisance and waste of energy. Light is provided to illuminate target areas on the street level where activities take place, yet light can also cause trespass to residents at the floors above. While regulations are beginning to cover light design, simulation tools for the outdoor environment have also become more popular for assessing the design condition. Simulation tools allow visualisation of the impact of the selected light sources on those who are affected. However, this cause-and-effect relationship is not easy to determine in the complex urban environment. The current work offers a simple methodology that takes site survey results and correlates them with the simulation model to determine lighting impact on the investigated area in 3D. Four buildings in two mixed commercial and residential streets in Hong Kong were studied. Data collection from each residential building requires lengthy work and permission from each household. Therefore, a valid lighting simulation model could help determine the light pollution impact in the area. A light model using DIALux is developed and calibrated by correlating the simulated data with the actual measured data. The correlation value R2 achieved ranged from 0.95 to 0.99, verifying the accuracy of this model and matched from 340 lx to 46 lx for the lower to higher floors of one building and 10 lx to 4 lx for floors of another building. This model can also be applied to human health research, by providing light-level data on residential windows in an area or determining the environmental impact of a development project.

Light pollution spatial impact assessment in Hong Kong: Measurement and numerical modelling on commercial lights at street level.

With rapid urbanization, the use of external lighting to illuminate cities for night-time activity is on the rise worldwide. Many studies have suggested the excessive use of external lighting causes light pollution, which harms human health and leads to energy wastage. Although more awareness has been raised, there are not many regulations and guidelines available. As one of the cities most affected by light pollution in the world, Hong Kong has started exploring this issue within the general and business communities. However, studies that quantitatively evaluate the problem of light pollution in this city are lacking. This study aimed to assess light pollution quantitatively through measurement and numerical modelling. To achieve this, measurement protocols were developed, and site measurements were carried out in one of the known problem areas, Sai Yeung Choi Street in Mong Kok district. Through this exercise, both vertical and horizontal illuminances on the street level and the light distribution along the street were determined. An average level of 250 lx for the vertical illuminance was found, which was 3-4 times higher than the recommended brightness for normal activity. The light environment of the measured area was also modelled with the simulation program DIALux. This effort complemented the measurements by providing a means to increase the resolution on the light variation and to visualize light pollution in a 3D environment. The simulation results were verified by correlating the numerical model with measurements. The correlated model was exercised in a subsequent sensitivity study to predict possible outcomes with changing lighting pattern and lighting lumen level. This study serves to quantify this issue, which helps with the further development of effective solutions.

Profiling Airborne Microbiota in Mechanically Ventilated Buildings Across Seasons in Hong Kong Reveals Higher Metabolic Activity in Low-Abundance Bacteria.

Metabolically active bacteria within built environments are poorly understood. This study aims to investigate the active airborne bacterial microbiota and compare the total and active microbiota in eight mechanically ventilated buildings over four consecutive seasons using the 16S rRNA gene (rDNA) and the 16S rRNA (rRNA), respectively. The relative abundances of the taxa of presumptive occupants and environmental origins were significantly different between the active and total microbiota. The Sloan neutral model suggested that ecological drift and random dispersal played a smaller role in the assembly of the active microbiota than the total microbiota. The seasonal nature of the active microbiota was consistent with that of the total microbiota in both indoor and outdoor environments, while only the indoor environment was significantly affected by geography. The relative abundances of the active and total taxa were positively correlated, suggesting that the high-abundance members were also the greatest contributors to the community-level metabolic activity. Based on the rRNA/rDNA ratio, the low-abundance members consistently had a higher taxon-level metabolic activity than the high-abundance members over seasons, suggesting that the low-abundance members may have the ability to survive and thrive in the indoor environment and their impact on the health of occupants cannot be overlooked.

Sensitivity analysis of influence factors on multi-zone indoor airflow CFD simulation.

Computational fluid dynamics (CFD) is a powerful tool for performing indoor airflow analysis. The simulation results are usually validated with measurement results for accuracy in reflecting reality. When conducting CFD for simulating air flow in a multiple-zone indoor environment with different boundary conditions in different regions, the validation of the CFD model becomes sophisticated. To improve the accuracy of the simulation, boundary conditions need to be adjusted based on how significant the influence factors are affecting the multi-zone CFD model, which few studies have been conducted on. The objective of this study is to investigate the impact of influence factors on temperature and carbon dioxide concentration distribution of a validated CFD model of a typical office floor using ANSYS Fluent. This study provides insights on how to fine-tune a complex model to reflect the actual air flow and how the air quality and human comfort in different zones on the same floor could be affected by influence factors. The influence factors investigated are: (1) size of door gaps, (2) solar radiation and (3) number and orientation of occupants. The velocity variations caused by different door gap sizes were studied for improving multi-zone simulation accuracy by adjusting door gap sizes. To study the significant impact of solar heat on multi-zone environment, the sensitivity of different regions of the office floor to solar heat amount and distribution was analyzed by conducting solar analysis under different weather conditions. Impact of occupants on temperature and carbon dioxide concentration distributions in multi-zone environment were investigated by considering different numbers and facing directions of occupants in different regions of the office floor. In addition, this study demonstrates how to modify the influence factors efficiently using building information modeling (BIM).

Airborne Bacteria in Outdoor Air and Air of Mechanically Ventilated Buildings at City Scale in Hong Kong across Seasons.

Studies of the indoor airborne microbiome have mostly been confined to a single location and time point. Here, we characterized, over the course of a year, the geographic variation, building-function dependence, and dispersal characteristics of indoor and outdoor airborne microbiomes (bacterial members only) of eight mechanically ventilated commercial buildings. Based on the Sloan neutral model, airborne microbiomes were randomly dispersed in the respective indoor and outdoor environments and between the two environments during each season. The dominant taxa in the indoor and outdoor environments showed minor variations at each location among seasons. The airborne microbiomes displayed weak seasonality for both indoor and outdoor environments, while a weak geographic variation was found only for the indoor environments. Source tracking results show that outdoor air and occupant skin were major contributors to the indoor airborne microbiomes, but the extent of the contribution from each source varied within and among buildings over the seasons, which suggests variations in local building use. Based on 32 cases of indoor airborne microbiome data, we determined that the indoor/outdoor (I/O) ratio of PM2.5 was not a robust indicator of the sources found indoors. Alternatively, the indoor concentration of carbon dioxide was more closely correlated with the major sources of the indoor airborne microbiome in mechanically ventilated environments.

Numerical simulation of the urine flow in a stented ureter.

When a stent is implanted in a blocked ureter, the urine passing from the kidney to the bladder must traverse a very complicated flow path. That path consists of two parallel passages, one of which is the bore of the stent and the other is the annular space between the external surface of the stent and the inner wall of the ureter. The flow path is further complicated by the presence of numerous pass-through holes that are deployed along the length of the stent. These holes allow urine to pass between the annulus and the bore. Further complexity in the pattern of the urine flow occurs because the coiled "pig tails," which hold the stent in place, contain multiple ports for fluid ingress and egress. The fluid flow in a stented ureter has been quantitatively analyzed here for the first time using numerical simulation. The numerical solutions obtained here fully reveal the details of the urine flow throughout the entire stented ureter. It was found that in the absence of blockages, most of the pass-through holes are inactive. Furthermore, only the port in each coiled pig tail that is nearest the stent proper is actively involved in the urine flow. Only in the presence of blockages, which may occur due to encrustation or biofouling, are the numerous pass-through holes activated. The numerical simulations are able to track the urine flow through the pass-through holes as well as adjacent to the blockages. The simulations are also able to provide highly accurate results for the kidney-to-bladder urine flow rate. The simulation method presented here constitutes a powerful new tool for rational design of ureteral stents in the future.