Just as children eventually learn that covering their eyes does not make them invisible, we as adults have realized that just because harmful substances are "out-of-site" it does not necessarily mean they are gone for good. As we expanded our ability to think abstractly we began to consider how our actions affect our future and the lives of future generations. For example, we established procedures for the handling and disposal of high level radioactive waste and other hazardous materials because of the threat such materials pose to the environment. To date, however, the effect of atmospheric pollutants on groundwater supplies has been virtually ignored. Atmospheric pollution sources include, but are not limited to, smoke stack emissions, releases from power plants, weapons testing and manufacturing, fires, explosions, and deflation from tailings, spills and playas. This study evaluates the potential for groundwater to be contaminated by a point-source atmospheric emission. Pollutant concentrations in groundwater are estimated using a Gaussian model of atmospheric transport, a transfer function model for transport through the unsaturated zone, and a two-dimensional groundwater flow model based on Darcy's law to simulate transport in the saturated groundwater system. A sensitivity analysis of the composite atmospheric-groundwater transport model suggests that the most important factors influencing the susceptibility of a groundwater system to contamination by an aerosol source are: the concentration of the source, the amount of recharge, the depth to the water-table, and the velocity distribution in the unsaturated zone. This study indicates a significant potential for pollution of groundwater systems by aerosols. Shallow aquifers are especially vulnerable; however, deeper aquifers where rapid travel times through the unsaturated zone exist are also susceptible to aerosol contamination. / text

published_or_final_version / Politics and Public Administration / Master / Master of Public Administration

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Public Health / Master / Master of Public Health

In the last century, there has been a rapid growth and development in economy and modern technology around the world. This phenomenon helped improving wealth and living standard but also brought pollutions to the society and the environment. Among various kinds of pollution, air pollution takes a larger proportion. Therefore, there is increasing concern about the ventilation and pollution removal behavior in the urban environment. Among different academic studies performed, the use of computational fluid dynamics (CFD) had become more popular. Since wind tunnel experiments serve as validations for CFD results, this thesis developed the technique required for wind tunnels experiments and to investigate the pollutant removal related to urban geometry, as well as the technique for gas sampling to examine the distribution of pollutants in urban boundary layer over idealized two-dimensional (2D) street canyons. Three specific tasks are archived to accomplish the above objectives. The first task was to extend the wind tunnel in the Department of Mechanical Engineering, the University of Hong Kong. An extension duct was designed to increase the length of the test section in which the reduced-scale model could be installed. The dimensions of the test section were specified according to the required length for fully developed flow inside the test section, the environment in the laboratory and the original wind tunnel conditions. The extension duct was then constructed and mounted, with the wind profile inside the test section obtained afterwards. After construction of the extended test section for experimental purposes, the second task was to examine the pollutant transport behaviors from the ground level of idealized 2D urban street canyons to the urban atmospheric boundary layer (ABL) using both laboratory wind tunnel measurements and CFD. Movable rectangular aluminum blocks were placed in the wind tunnel in cross-flow to construct street canyons of different building-height-to-street-width (aspect) ratios. Wetted filter papers were applied on the surface of the blocks inside the street region, modeling the source of pollutant emission inside the street canyons. The wind tunnel and CFD results complemented each other to elucidate the pollutant removal mechanism that is in line with other results available in literature. From the experimental results obtained, scaling effect was observed in the mass transfer behaviors even the flows had fulfilled kinematic similarity. A new indicator, the scaled overall pollutant removal coefficient, was formulated for the comparison of pollutant removal performance. The improved agreement in the comparison with the CFD results showed that the scaled overall pollutant removal coefficient could be used to account for the scaling effects occurred in laboratory experiments at finite Reynolds number (〖10〗^(3 ) to 〖10〗^(5 ) in this study) for comparison of pollutant removal performance. The behavior of pollutants inside the street canyons was studied; however, the pollutant concentration inside a street could be affected by the pollutant source in another street, even there were several streets away from it. The pollutant escaped from the source street could act as air entrainment into other streets, affecting the air quality. The concentration profile correlated to the street geometry was thus studied. The last task of this dissertation was to study the effect of urban geometry on the concentration profile of the urban ABL by means of gas dispersion experiments. Experiments were carried out in the wind tunnels of the Department of Mechanical Engineering and Department of Civil Engineering with different sets of experimental models used. A special gas emission source was constructed in order to simulate the linear source due to busy traffic in the street regions. The required gas sampling techniques were also studied throughout the measurement. Trial experiments were carried out and preliminary results had been obtained. Furthermore, the pollutant concentration profiles downstream from a linear pollutant source in an idealized 2D street canyon were also measured. Throughout the experiments, different designs of line source were tested and factors affecting the experimental results were considered. One of the line source designs was adopted and the pollutant concentrations in street canyons of different aspect ratios were observed. The concentration decreases rapidly with increasing distance from the roof but then increases to steady value. The average pollutant concentration over the concentration profile was different at different aspect ratios. It is believed that its performance depends on the pollutant removal behavior from street regions. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

Objective: To present a systematic review of existing literature that investigates biological plausibility of prenatal hazardous air pollutants’ (HAPs) exposure, in the etiology of autism spectrum disorder (ASD) and related outcomes. Method: Electronic databases Pubmed, Biomed Central and National Database for Autism Research, and grey literature pertaining to air pollution association with ASD and related outcomes were searched using specific keywords. The search included 190 HAPs as defined by The Clean Air Act Amendments of 1990 [U.S.Environmental Protection Agency (EPA) 1994] including air pollutants CO, SO2, NOx, O3 and Particulate Matter (PM). Studies selected for systematic review were assessed on quality and causality. Result: Total of 628 articles from electronic search and 16 articles from grey literature were retrieved. 12 studies that cleared the inclusion and exclusion criteria were systematically reviewed using the PRISMA checklist. Outcomes considered included ASD, Attention Deficit Hyperactivity Disorder, social behavior, social interaction, child behavior, communication, cognitive development, attention problems, mental and psychomotor development, and social competence. Studies were from two countries, United States of America and Spain. Study design was case control and cohort study. Follow up duration for cases ranged from in-utero to less than 9 years. Exposure was measured in ambient air using predictive models and cord blood. Although there were discrepancies in the studies, related to strength of association, analysis and covariates adjusted, the association between air pollution and ASD related outcomes could not be dismissed. Most studies lacked information on blinding when quality was assessed and lacked consistency when assessed on causality, while scored well on temporality and biological plausibility. Discussion: Evidence suggests HAPs are capable of transplacentally affecting cognitive function, especially traffic related pollutants. Study design, sample size, response rate, exposure misclassification, failing to adjusting covariates related to lifestyle, nutrition and other chemical exposures have influenced the estimates and the strength of association. Shortcomings of this review are the English language restriction and single reviewer on study selection process and assessments. Immuno-toxic, neuro-toxic and endocrine disrupting properties of these HAPs necessitates comprehensive prospective studies especially in Hong Kong with the rising prevalence of ASD and ever high reported air pollution indexes. Conclusion: Repeated studies were carried out on the same cohorts and studies were concentrated in U.S.A. On account of a lack of consistency, it is difficult to confirm whether air pollution is a plausible candidate for prenatal exposure in ASD. (Abstract of 391 words) / published_or_final_version / Public Health / Master / Master of Public Health

Objective To investigate whether traffic pollutants have any effect on human cognitive functions and behavior by performing a systematic review on existing research studies. Methods Research articles were identified through four databases – CINAHL Plus, Academic Search Premier and MEDLINE via EBSCOhost and Pubmed using the online electronic resources of the libraries of the Hong Kong University. A total of 119 articles from Pubmed and 86 articles from EBSCOhost were identified, and 72 and 64 studies after limits were applied. The studies used a variety of measures to assess the effects of traffic-related air pollution and cognitive functions and behaviors in both children and adults. Results There were 19 articles in total in the systematic review – 13 on children (aged from 1- 17 years) and six on adults (aged from 26 - 83.5 years). Data were employed from nine different countries. Although there were some discrepancies in the results, there was evidence of the effects of traffic-related air pollution on the brain. Conclusions The causal relationship between traffic-related air pollution and cognitive decline cannot be clearly determined. The systematic review however, generated evidence to support the hypothesis that traffic-related air pollution may affect cognitive development in children, increase risks of behavioral disorders in both children and adults, and increase the rate of cognitive decline in older adults. As a result, this systematic review suggests that the research findings have important implications in the development of public health policy and practice. / published_or_final_version / Public Health / Master / Master of Public Health

Background Epidemiological studies have shown that air pollution was associated with both mortality and morbidity of various diseases including cardiovascular diseases, respiratory diseases and cancers. However, the various traffic-related exposure indicators are difficult to compare due to the diversity of study areas, populations, measures of traffic exposures and confounders. Moreover, most of the studies were conducted in the western and European countries. Few studies using the traffic density as surrogate of traffic-related exposure for effects on mortality risk have been performed in Asia and none has been performed in Hong Kong. Objective This study aims to assess the association between the traffic-related exposure and the all-cause and cause-specific mortality risk in the densely populated city of Hong Kong, where traffic emission plays an important role on the ambient air quality. Methods Three traffic-related indicators were employed including: Road Density (RD) in terms of total length of roads divided by Tertiary Planning Unit (TPU) area; Traffic Density (TD) defined by road lengths times the Annual Average Daily Traffic (AADT) and divided by the TPU area; and Vehicle Density (VD) means average AADT over TPU area. Each exposure was divided into three groups according to tertiles. An ecological study was conducted first with population census and mortality data. The age-sex standardized all-cause and cause-specific mortality rate was calculated for each TPU with the whole Hong Kong death rate in 2010 as the standard. Poisson regression models were performed to estimate risks of traffic-related exposure with adjustment of the marital status, race, education, housing tenure, and median household income. After the TPU-level analyses, a cohort with 64,888 elderly subjects being followed up from 1998 to 2012 was used to assess the association with further control for the individual-level factors including age, sex, education, income, housing, and smoking. The Multilevel Cox proportional regression models were built with adjustment for both the individual level confounders and TPU-level covariates. Excess risks from both models were reported. Results Higher exposure areas were found in the northern part of Hong Kong Islands and the inner city of Kowloon peninsula. Statistically significant association between traffic-related exposure and mortality was observed. For the investigation in the general population, the all-nonaccidental cause mortality was associated with 43% (95% confidence interval 37-48%) and 50% (44-56%) excess risk for areas with the middle and high level TD exposure compared with the low level group. The association was similar with measures of RD and VD. For the cause-specific mortality, the respiratory deaths showed a higher risk when compared with the cardiovascular and cancer deaths. For the elderly subjects, the excess risk of all-nonaccidental causes relative to the low level exposure of 13% (1-26%) and 12% (0-25%) for the middle and high level exposure were smaller when compared with the risk in the general population. Conclusion There is an association between traffic-related exposure and mortality in the general and older population of Hong Kong. In future comprehensive investigations with the individual-level exposure measure are needed. Assessment on the younger population should also be studied. / published_or_final_version / Public Health / Master / Master of Philosophy

Flows and pollutant dispersion over flat rural terrain have been investigated for decades. However, our understanding of their behaviours over urban areas is rather limited. Most cases have either focused on street level or in the roughness sub-layer (RSL) of urban boundary layer (UBL). Whereas, only a handful of studies have looked into the coupling between street-level and UBL-core dynamics, and their effects on pollutant dispersion. In this thesis, computational fluid dynamics (CFD) is employed to examine the flows and pollutant transport in and over urban roughness. Idealised two-dimensional (2D) street canyons are used as the basic units fabricating hypothetical urban surfaces. A ground-level passive and chemically inert pollutant source is applied to simulate the flows and pollutant dispersion over rough surfaces in isothermal condition. Large-eddy simulation (LES) with the one-equation subgrid-scale model is used to solve explicitly the broad range of scales in turbulent flows. Arrays of idealized street canyons of both uniform and non-uniform building height are used to formulate a unified theory for the flows and pollutant dispersion over urban areas of different morphology. The geometry of roughness elements is controlled by the building-height-to-street-width (aspect) ratio (0.083 ≤ AR ≤ 2) and/or the building height variability (BHV = 0.2, 0.4 and 0.6), in which the characteristic regimes of skimming flow, wake-interference and isolated roughness are covered. A detailed analysis on the roof-level turbulence structure reveals parcels of low-speed air masses in the streamwise flows and narrow high-speed down-drafts in the urban canopy layer, signifying the momentum entrainment into the street canyons. The decelerating streamwise flows in turn initiate up-drafts carrying pollutants away from the street canyons, illustrating the basic pollutant removal mechanism in 2D street canyons. Turbulent transport processes, in the form of ejection and sweep, are the key events governing the exchanges of air and pollutant of street canyon. Air exchange rate (ACH) along the roof level is dominated by turbulent transport, in particular over narrow street canyons. The LES results show that both the turbulence level and ACH increase with increasing aerodynamic resistance defined in term of the Fanning friction factor. At the same AR, BHV greatly increases the friction factor and the ACH in dense built areas (AR ≤ 0.25). The turbulence intensity is peaked on the windward side of street canyons that does not overlap with the maximum velocity gradient near the leeward building corners, suggesting the importance of background turbulence in street-level ventilation. Over the building roughness, pollutant plume dispersion after the ground-level area source in cross flows resumes the self-similar Gaussian shape in the vertical direction in which the vertical plume coverage is proportional to the square root of downwind distance in the streamwise direction. Moreover, the vertical dispersion coefficient is proportional to the one-fourth power of friction factor over idealised street canyons. Conclusively, friction factor can be used to parametrise ventilation and pollutant dispersion over urban areas. / published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Objective Large quantities of epidemiological studies manifest that indoor and outdoor air pollutants may trigger and aggravate asthma symptoms, whose mechanism, however, has not been completely made clear yet. As shown by the result of the experiment in which in-vitro cells and animals are exposed to high-density air pollution, the triggering effect of air pollution on asthma is associated with inflammatory reaction, IgE expression and regulation pathways. However, there is a lack of evidence from population studies to support that association. This study plans to conduct continuous monitoring over indoor and outdoor air pollutants facing the asthmatic children from Beijing with a view to carry out an overall assessment of their exposure to air pollutants. Meanwhile, biomarkers which are directly reflecting airway inflammation as well as the signal molecules which are related to IgE expression and regulation are monitored. The next step is to establish an exposure-effect relationship to explore the trigger effect of air pollutants on childhood asthma. Methods 1. Questionnaires were used to collect general information (including age, drug use, indoor home decoration, passive smoking, diet during the study, indoor mildew, allergic history, history of diseases and family heredity history) in 60 asthmatic children (males, Han nationality, aged 5 to 14 years)from Beijing who were recruited into this study. 2. A comprehensive evaluation was conducted on their exposure levels of air pollutants by continuous monitoring of indoor PM2.5, black carbon, benzene, toluene, xylene and formaldehyde in their houses and collecting monitoring data with respect to PM2.5, PM10, NO2and SO2at air quality monitoring sites near their houses. Benzene, toluene and xylene were measured by two-stage thermal desorption-gas chromatography (GC), formaldehyde by AHMT spectrophotometry, mass concentration of PM2.5by gravimetric method, black carbon in PM2.5by multi-wavelength absorption spectroscopy. The concentration data of ambient outdoor air pollutants were available from the real-time air quality publishing platform of Beijing Municipal Environmental Monitoring Center. 3. Exhaled FeNO of asthmatic children were taken as biomarkers reflecting their airway inflammation. FeNO was measured by electrochemical method (off-line monitoring). 4. Trigger effect of air pollution on IgE signaling pathway of asthmatic children was investigated by determining signal molecules of two signaling pathways related to IgE expression and regulation in peripheral serum. Signal molecules were determined by ELISA. 5. Confounding factors were controlled by stratification analysis and multiple linear regression model, and a comprehensive analysis was conducted of the triggering effect of air pollution on children asthma. Results 1. During the research, as for subjects, concentrations of indoor PM2.5, BC, formaldehyde, benzene, toluene, m-, p-and o-xylenes were 55.3±29.9 μg/m3, 3.8±1.4 μg/m3,62.2±42.7 μg/m3, 13.1±15.9 μg/m3, 18.7±16.7 μg/m3, 7.9±7.9 μg/m3and 3.1±5.0 μg/m3, respectively. The7-day weighted average concentrations of outdoor PM2.5, PM10, SO2and NO2were 101.3±87.6μg/m3, 152.8±88.4μg/m3, 48.6±39.8 μg/m3and 63.1±27.7μg/m3, respectively. There was a significant correlation between 7-day weighted average concentrations of indoor and outdoor PM2.5 simultaneously (r=0.697, P<0.001), with a indoor/outdoor PM2.5concentration ratio (I/O ratio) of 0.86±0.39 (P25-P75ranging from 0.62 to 1.01). 2. After adjusting for such influencing factors as age, types of asthma, and season, analysis of all subjects found that FeNO was significantly positively correlated with either benzene in indoor air, or PM2.5, SO2and NO2 in ambient outdoor air. Separate analysis of subjects untreated with inhaled corticosteroids (ICSs) found that FeNO was significantly positively correlated with PM2.5, SO2and NO2 in ambient outdoor air, while this correlation was not significant in the ICS-treated group. 3. In serum, there was a significantly positive correlation between signal molecules in the two regulatory pathways of IgE expression. After adjusting for such influencing factors as age, types of asthma, and passive smoking. No effect of air pollutants on level of signaling molecule was observed in this study. Conclusion Monitoring results of indoor and outdoor air pollutants show that, at a high level of exposure to air pollutants, exposure of asthmatic children to indoor and outdoor air pollutants may cause or aggravate the airway inflammation. Administration of ICSs can control or attenuate the airway inflammation caused by air pollutants in asthmatic children, while the level of signaling molecule in the regulatory pathway of IgE expression in serum may not be an ideal marker for reflecting the trigger effect of air pollution on children asthma. / published_or_final_version / Public Health / Master / Master of Public Health