Subtropical Urban Environment Research Articles

On the cooling energy impacts of combined urban heat mitigation strategies in subtropical urban building environment

Regional climate change leads to more extreme urban heat in desert cities. This affects the building's performance negatively through an increase in cooling energy consumption. To our knowledge, this is the first study investigating the impacts of implementing combined urban heat mitigation strategies of cool materials and increased vegetation on the cooling load demands of 40-various types of buildings in Dubai downtown. Four urban heat mitigation scenarios have been conducted in combination with a base case scenario to examine the effectiveness of the combined strategies in reducing the cooling load demand by using the climatic data from weather research and forecasting model coupled with single layer urban canopy model (WRF/SLUCM) in CitySim. Results revealed that for non-insulated buildings there was an estimated 17.2% to 36.4% reduction in cooling energy demand whereas insulated buildings have an average reduction in energy demand ranging between 15.5% and 29.1%. This reduction in cooling energy consumption is higher when compared with other mitigation techniques like additional urban vegetation and modified cool materials.

Cooling Energy Benefits of Increased Green Infrastructure in Subtropical Urban Building Environments

Due to urban warming, the energy demand for cooling buildings is rising. The current study used CitySim (building energy model) to estimate the cooling energy requirements for 40 buildings in downtown Dubai using high-resolution climate data from weather research and forecasting (WRF) coupled with the single layer urban canopy model (SLUCM). Simulating the four mitigation scenarios allowed for the examination of the reduction in cooling load caused by the addition of greenery at a rate ranging from 25% to 100%. The insulated building’s cooling demand reduced by a maximum of 13.89% under 100% GI (M4). Scenario M4 resulted in a reduction of 4.6 kWh/m2 and 3.1 kWh/m2 for the non-insulated and insulated low-rise residential buildings, respectively, while the high-rise buildings saw a reduction of 3.09–4.91 kWh/m2 for the non-insulated and 2.07–3.09 kWh/m2 for the insulated buildings. This study offers a potential remedy to deal with the problem of urban heating in subtropical environments.

Spatial pattern assessment of dengue fever risk in subtropical urban environments: The case of Hong Kong

Dengue fever, a mosquito-borne fatal disease, brings a huge health burden in tropical regions. With global warming, rapid urbanization and the expansion of mosquitoes, dengue fever is expected to spread to many subtropical regions, leading to increased potential health risks on local populations. So far, limited studies assessed the dengue fever risk spatially for subtropical non-endemic regions hindering the development of related public health management. Therefore, we proposed a spatial hazard-exposure-vulnerability assessment framework for mapping the dengue fever risk in Hong Kong. Firstly, the spatial distribution of the habitat suitability for Aedes albopictus, the mosquito proxy for the dengue fever hazard, was predicted using a species distribution model (e.g., MaxEnt) relying on a list of variables related to local climate, urban morphology, and landscape metrics. Secondly, the spatial autocorrelation between high dengue hazard and high human population exposure in urban areas was measured. Finally, the dengue fever risk was assessed at community scale by integrating the results of vulnerability analysis basing on census data. This approach allowed the identification of 17 high-risk spots within Hong Kong. The landscape metrics about land utilities and vegetations, and urban morphological characteristics are the influential factors on the spatial distribution of dengue vector. In addition, the underlying factors behind each hot spot were investigated, and specific suggestions for dengue prevention were proposed accordingly. The findings provide a useful reference for developing local dengue fever risk prevention measures, with the proposed method easily exportable to other high-density cities within subtropical Asia and elsewhere.

Foliar Uptake of Toxic Metals Bound to Airborne Particulate Matter in an Urban Environment

In this research, the foliar uptake patterns of three toxic metals (Pb, Cd, and Cu) bound to airborne particulate matter (PM) were investigated using two evergreen tree species (Senna siamea and Alstonia scholaris) at six different locations (two residential, traffic, commercial, and industrial) plus one control site in a subtropical urban environment. The concentrations of Pb, Cd, and Cu were measured from foliar dust, leaf, road dust, and soil samples collected from the target sites over two consecutive years. Their temporal variations in leaves were examined at monthly, seasonal, and annual scales. The data were evaluated statistically by One-way Analysis of variance ANOVA and correlation analysis along with enrichment factor (EF). There were significant variations on the monthly as well as the seasonal basis. Accordingly, PM-bound toxic metals in leaves come from an airborne route. In addition, leaves of S. siamea showed a moderately improved accumulation pattern relative to A. scholaris. This study suggests that these plants can be used efficiently as basic tools to assess the pollution and associated behavior of PM-bound toxic metals in an urban environment.

Cytological and Histopathological Characteristics of Canine Transmissible Venereal Tumour in Male and Female Dogs Before and After Vincristine Treatment

Canine transmissible venereal tumour (CTVT) is a neoplasia naturally transmitted in susceptible dogs through coitus. CTVT has a worldwide distribution, with a high prevalence in tropical and sub-tropical urban environments. The study aimed at evaluating CTVT lesions in local breeds of dogs and to assess morphological changes based on sex before and after administration of vincristine sulphate. Clinical and gross morphology, fine needle aspirates cytology (FNAC) and routine histopathology methods were used. Two FNAC and histopathological microscopic slide sections from each of the seven sampled dogs were stained with Giemsa stain and Hematoxylin and Eosin. All dogs were treated with vincristine once weekly over a six weeks period after which clinical morphological and histopathological changes were assessed. Grossly, before treatment the tumour masses appeared irregular, cauliflower like with tendency to bleed, sizes ranged from ≥5cm to ≤2cm with or without metastasis to regional lymph nodes. Cytologically, the tumours had homogenous, sheet-like cellular mass. Cytoplasm with punctate vacuoles, anisokaryosis with anisonucleoliosis and coarse to reticulate nuclear chromatin were seen. Lymphocytoid cell pattern was dominant cell type. Histopathology showed sheets of round cells with nuclear and cytoplasmic variations. Histopathology of the treated dog revealed hyper-cellularity, absence of nucleoli, prominent mitotic figures, reduced cell size and presence of inflammatory cells. There was no difference on the cellular changes after vincristine treatment between female and male dogs. Cytology and histopathology showed that vincristine sulphate suppresses the development of tumour through alteration of cellular morphology with no difference between male and female dogs.

BARRIER TREATMENTS USING COMBINED LAMBDA-CYHALOTHRIN AND PYRIPROXYFEN REDUCE PERIDOMESTIC AEDES MOSQUITOES IN A SUBTROPICAL ENVIRONMENT

Barrier treatment of vegetation using lambda-cyhalothrin has been shown to be effective at reducing adult mosquito populations in the US. However, recent investigations have indicated that standard residual adulticide barrier treatments may be enhanced when combined with an insect growth regulator targeting immature stages that could be transferred to immature habitat by adults contacting treated surfaces. We conducted field trials at residential sites in a subtropical urban environment in north central Florida treating blocks of vegetation with residual sprays of lambda-cyhalothrin (Demand® CS) and pyriproxyfen (Archer®) alone and in combination treatments to determine their efficacy against peridomestic mosquitoes. The combined treatment resulted in consistent approximately 100% reduction in Aedes mosquito eggs for 16 wk post-treatment compared to not significantly lower but more variable reductions at alone treatment sites.

Atmospheric transport and deposition of microplastics in a subtropical urban environment

As an issue of great concern, microplastics pollution has emerged as a key environmental challenge of our time. The atmosphere is a significant compartment in the global cycle of microplastics, however, studies on the transport and deposition of airborne microplastics is limited. In the present work, atmospheric wet and dry deposition of microplastics were analyzed over one year in an urban environment of megacity Guangzhou, China. The atmospheric deposition fluxes of microplastics ranged from 51 to 178 particles/m2/d (mean: 114 ± 40 particles/m2/d). Fibers, fragments, films and microbeads were observed in the deposition samples, with fibers being the most abundant microplastics, accounting for 77.6 ± 19.1% of the total. The chemical composition of microplastics were identified using micro Fourier transform infrared spectrometer. 78.7% of the fibrous microplastics were derived from petrochemicals and most were polyethylene terephthalate (polyester), suggesting that textiles (e.g., clothes and curtains) were likely the main source. The results of back-trajectory analysis indicated that city rivers may act as secondary sources of airborne microplastics. Though no significant correlation was found between atmospheric microplastic deposition and meteorological factors such as rainfall and wind events, these factors were suggested to be positive drivers for the transport and deposition of airborne microplastic.

The influence of wind speed on new particle formation events in an urban environment

New particle formation (NPF) is a common occurrence in urban environments where it is promoted by a ready supply of gaseous precursors such as sulfuric acid, ammonium and volatile organic compounds originating mainly from motor vehicle emissions. In this paper, we investigate the influence of wind speed on the occurrence of NPF events in a subtropical urban environment. The analysis was based on a large data set obtained with a neutral cluster and air ion spectrometer (NAIS) over 485 days of observations, out of which NPF events were observed on 213 days. Particles formation was most likely to occur during the morning hours and we observed NPF events between 8 am and noon on 123 of these days. In order to assess its influence, we estimated the mean wind speed between 8 and 9 am on these 123 days and on the days with no NPF. We found a statistically significant difference in average wind speeds during days with NPF (1.31 m s−1) and days with no NPF (1.84 m s−1) (p < 0.05). Several studies have shown that increasing wind speed enhances NPF in polluted megacities by removing pre-existing particles. Our observations indicate that this effect is less important in smaller cities, so that higher wind speeds can mitigate NPF by the removal of condensable gases. The wind speed does not affect the rate of NPF in clean environments.

Differentiating between particle formation and growth events in an urban environment

Abstract. Small aerosols at a given location in the atmosphere often originate in situ from new particle formation (NPF). However, they can also be produced and then transported from a distant location to the point of observation where they may continue to grow to larger sizes. This study was carried out in the subtropical urban environment of Brisbane, Australia, in order to assess the relative occurrence frequencies of NPF events and particle growth events with no NPF. We used a neutral cluster and air ion spectrometer (NAIS) to monitor particles and ions in the size range 2–42 nm on 485 days, and identified 236 NPF events on 213 days. The majority of these events (37 %) occurred during the daylight hours with just 10 % at night. However, the NAIS also showed particle growth with no NPF on many nights (28 %). Using a scanning mobility particle sizer (SMPS), we showed that particle growth continued at larger sizes and occurred on 70 % of nights, typically under high relative humidities. Most particles in the air, especially near coastal locations, contain hygroscopic salts such as sodium chloride that may exhibit deliquescence when the relative humidity exceeds about 75 %. The growth rates of particles at night often exceeded the rates observed during NPF events. Although most of these night time growth events were preceded by day time NPF events, the latter was not a prerequisite for growth. We conclude that particle growth in the atmosphere can be easily misidentified as NPF, especially when they are monitored by an instrument that cannot detect them at the very small sizes.

BIM-aided variable fuzzy multi-criteria decision making of low-carbon building measures selection

Low-carbon building (LCB) has been regarded as an innovative and practical approach to reducing building carbon emissions. The design decision making for LCBs should consider various criteria which however are often associated with uncertain information. Little research has examined multi-criteria decision making (MCDM) in selecting LCB measures, particularly in high-density subtropical urban environments. That selection process is inhibited by the lack of consensus on assessing the performance of LCB options and of an efficient decision support system. The aim of this paper is to develop a BIM-aided variable fuzzy MCDM model for selecting LCB measures. The paper identifies the key criteria and alternatives to systematically assess LCB measures. Five criteria and nine alternatives were identified within the context of high-rise commercial buildings in Hong Kong, which are centralized on technical, economic and environmental aspects of building performance. With the use of BIM and eQUEST, the paper develops a MCDM model based on variable fuzzy Preference ranking organization method for enrichment evaluation (PROMETHEE) to improve the robustness and practicality of decision results over traditional methods. The developed model is validated utilizing a real-life project case in Hong Kong. The results suggest that the developed model will provide design decision makers with a consolidated tool for selecting LCB measures.

Anthropogenic and Biogenic Features of Long-Term Measured CO Flux in North Downtown Houston, Texas.

Long-term urban carbon cycle studies remain rare despite the importance of carbon for energy, air quality, and climate change. To study spatial and temporal variations of energy and carbon fluxes in a subtropical urban environment, eddy covariance flux measurements were conducted north of downtown Houston, TX, using a tall radio-tower installation. The results of the first 2 yr of measurements show that both concentrations and fluxes of CO display typical seasonal and diurnal variations in urban areas. The seasonal variation of net CO flux is driven by steady anthropogenic emissions dominated by car traffic and human respiration, moderated by the local deciduous tree foliage. Weekday-weekend differences were observed in carbon fluxes, but not concentrations, while diurnal changes were dominated by rush-hour peaks from traffic and vegetation influences. Interestingly, CO and CO concentrations, but not CO flux, exhibited long-term declines, especially comparing pre- and post-Hurricane Ike periods. A directional analysis of CO fluxes revealed that the highest fluxes typically occurred from northwest directions, most likely due to emissions from small industrial sources. Car traffic as carbon source was revealed via correlations of CO with CO during the morning rush hours, and of CO flux with traffic counts during winter time. The influence of urban vegetation on net CO fluxes was identified via correlations with daytime photosynthetically active radiation due to photosynthesis, and with nighttime temperatures due to ecosystem respiration. The study site is a net source of CO throughout all seasons.

Insights into the growth of newly formed particles in a subtropical urban environment

Abstract. The role of different chemical compounds, particularly organics, involved in the new particle formation (NPF) and its consequent growth are not fully understood. Therefore, this study was conducted to investigate the chemical composition of aerosol particles during NPF events in an urban subtropical environment. Aerosol chemical composition was measured along with particle number size distribution (PNSD) and several other air quality parameters at five sites across an urban subtropical environment. An Aerodyne compact Time-of-Flight Aerosol Mass Spectrometer (c-ToF-AMS) and a TSI Scanning Mobility Particle Sizer (SMPS) measured aerosol chemical composition (particles above 50 nm in vacuum aerodynamic diameter) and PNSD (particles within 9–414 nm in mobility diameter), respectively. Five NPF events, with growth rates in the range 3.3–4.6 nm, were detected at two of the sites. The NPF events happened on relatively warmer days with lower condensation sink (CS). Temporal percent fractions of organics increased after the particles grew enough to have a significant contribution to particle volume, while the mass fraction of ammonium and sulfate decreased. This uncovered the important role of organics in the growth of newly formed particles. Three organic markers, factors f43, f44 and f57, were calculated and the f44 vs. f43 trends were compared between nucleation and non-nucleation days. K-means cluster analysis was performed on f44 vs. f43 data and it was found that they follow different patterns on nucleation days compared to non-nucleation days, whereby f43 decreased for vehicle-emission-generated particles, while both f44 and f43 decreased for NPF-generated particles. It was found for the first time that vehicle-generated and newly formed particles cluster in different locations on f44 vs. f43 plot, and this finding can be potentially used as a tool for source apportionment of measured particles.

Mapping the urban microclimatic spatial distribution in a sub-tropical high-density urban environment

Understanding the urban microclimatic spatial distribution and its impact on thermal comfort is important for integrating climatic consideration into urban design process. This article presents a case study in Tsim Sha Tsui and Tai Po of Hong Kong densely built-up areas to investigate the spatial distribution of microclimatic condition. Air temperature (Ta), wind speed (v), relative humidity (RH) and globe temperature (Tg) of 87 locations in two selected sites were measured on a summer day and a winter day respectively. Physiological Equivalent Temperature was calculated to analyse the thermal comfort condition in two sites. Both numerical simulation and geographical mapping approach were used for the estimation of the microclimatic spatial distribution. Results show that the influence of urban morphology on the microclimatic spatial distribution can be well investigated by using numerical simulation while geographical mapping based on measured data shows higher estimation accuracy due to the consideration of anthropogenic heat and other factors associated with human activities. In summary, this article presents a pragmatic approach of mapping the urban microclimatic spatial distribution that can be referenced by architects and urban designers to raise climatic considerations for designing better cities.

Using Mobile LiDAR Data for Rapidly Updating Road Markings

Updating road markings is one of the routine tasks of transportation agencies. Compared with traditional road inventory mapping techniques, vehicle-borne mobile light detection and ranging (LiDAR) systems can undertake the job safely and efficiently. However, current hurdles include software and computing challenges when handling huge volumes of highly dense and irregularly distributed 3-D mobile LiDAR point clouds. This paper presents the development and implementation aspects of an automated object extraction strategy for rapid and accurate road marking inventory. The proposed road marking extraction method is based on 2-D georeferenced feature (GRF) images, which are interpolated from 3-D road surface points through a modified inverse distance weighted (IDW) interpolation. Weighted neighboring difference histogram (WNDH)-based dynamic thresholding and multiscale tensor voting (MSTV) are proposed to segment and extract road markings from the noisy corrupted GRF images. The results obtained using 3-D point clouds acquired by a RIEGL VMX-450 mobile LiDAR system in a subtropical urban environment are encouraging.

Reduction of Solar UV Radiation Due to Urban High-Rise Buildings--A Coupled Modelling Study.

Solar UV radiation has both adverse and beneficial effects to human health. Using models (a radiative transfer model coupled to a building shading model), together with satellite and surface measurements, we studied the un-obstructed and obstructed UV environments in a sub-tropical urban environment featured with relatively high pollution (aerosol) loadings and high-rise buildings. Seasonal patterns of the erythemal UV exposure rates were governed by solar zenith angles, seasonal variations of aerosol loadings and cloud effects. The radiative transfer modelling results agreed with measurements of erythemal UV exposure rates and spectral irradiances in UVA and UVB ranges. High-rise buildings and narrow road width (height to width, H/W, ratios up to 15) reduced the modelled total UV (UVA+UVB) radiation and leave 10% of the un-obstructed exposure rate at ground-level at noon. No more than 80% of the un-obstructed exposure rate was received in the open area surrounded by 20-storey buildings. Our modelled reduction of UVB radiation in the urban environment was consistent with similar measurements obtained for Australia. However, our results in more extreme environments (higher H/W ratios) were for the first time reported, with 18% of the un-obstructed exposure rate remained at the ground-level center of the street canyon.

Numerical modelling of mean radiant temperature in high-density sub-tropical urban environment

Outdoor thermal comfort has been a widely concerned issue in tropical and subtropical cities. In order to assess the conditions of outdoor thermal comfort, quantitative information on different spatial and temporal scales is required. This paper employs a numerical model (SOLWEIG – SOlar and LongWave Environmental Irradiance Geometry) to examine the spatial and temporal variations of mean radiant temperature (Tmrt), as an indicator of radiant heat load and outdoor heat stress in high-density sub-tropical urban environment in summer. The SOLWEIG model is found to simulate the six-directional shortwave and longwave radiation fluxes as well as Tmrt very well. Simulation results show that urban geometry plays an important role in intra-urban differences in summer daytime Tmrt. Open areas are generally warmer than surrounding narrow street canyons. Street canyons are sheltered from incoming direct solar radiation by shading of buildings while open areas are exposed to intense solar radiation, especially along the sunlit walls where high Tmrt is observed due to reflected short-wave radiation and long-wave radiation emitted from the sunlit building walls. The present study confirms that there are great potential in using urban geometry to mitigate high radiant heat load and daytime heat stress in the compacted urban environment. In high-density subtropical cities where high daytime Tmrt causes severe thermal discomfort in summer, dense urban structures are able to mitigate the extremely high Tmrt and improve outdoor thermal comfort. However, the shading strategy has to be cautious about air ventilation in such a dense urban environment.

Temporal and spatial patterns of carbon dioxide mixing ratios in a subtropical urban environment during spring

Temporal and spatial patterns of carbon dioxide mixing ratios in a subtropical urban environment during spring

A BIM-integrated Fuzzy Multi-criteria Decision Making Model for Selecting Low-Carbon Building Measures

Low-carbon building (LCB) has been regarded as an innovative and practical approach to reducing building carbon emissions. The design decision-making for LCBs should consider various criteria which however are often associated with uncertain information. Little research has examined multi-criteria decision making (MCDM) in selecting LCB measures, particularly in high-density subtropical urban environments. That selection process is inhibited by the lack of consensus on assessing the performance of LCB options and of an efficient decision support system. The aim of this paper is to develop a BIM-integrated fuzzy MCDM model for selecting LCB measures. The paper identifies the key criteria and alternatives to systematically assess LCB measures. Five criteria and nine alternatives were identified within the context of high-rise commercial buildings in Hong Kong, which are centralized on technical, economic and environmental aspects of building performance. With the use of BIM and eQUEST, a MCDM model based on Fuzzy PROMETHEE is developed. The developed model is validated utilizing a real project case in Hong Kong. The results will provide design decision-makers with a consolidated tool for selecting LCB measures.

A multi-criteria decision framework for the selection of low carbon building measures for office buildings in Hong Kong

Purpose– This paper aims to develop a multi-criteria decision framework (MCDF) for the selection of appropriate low carbon building (LCB) measures for office buildings in Hong Kong.Design/methodology/approach– The research was carried out through a critical literature review and a case study with a low carbon office building project.Findings– In total, 26 LCB measures were identified, under the five groups of building envelope, heating, ventilating and air conditioning system, lighting and elevators, renewable energy and appliances. Also identified were 16 decision criteria, centred on the implementation-related, economic, environmental and production-related aspects. The identified measures and criteria, coupled with the information and business processes of office building project delivery, formed the conceptual MCDF. The MCDF was also verified using an office building project.Research limitations/implications– The limitation of this research was the absence of the energy bill which could help to further verify the model in the case study.Originality/value– The developed framework should add value to knowledge of the use of multi-criteria decision-making methods and support the design decision-making of selecting LCB measures for office building projects in Hong Kong. The findings should also inform LCB design in other hot and humid subtropical urban environments.

Seasonal characteristics of biogenic and anthropogenic isoprene in tropical–subtropical urban environments

Measurements of atmospheric isoprene and other selected volatile organic compounds (VOCs) were conducted in Taipei, a tropical–subtropical metropolis, to investigate diurnal variations, seasonal diversity and spatial differences in terms of the levels and sources of isoprene. Our study also investigated the responses of biogenic isoprene to both light flux and temperature in real urban settings that have a variety of plant species and traffic volumes. The robust ratio of isoprene/1,3-butadiene obtained from pure traffic emissions was used as a gauge to separate biogenic isoprene from traffic emissions. The four seasonal measurements at a typical urban site in the city showed that biogenic contributions overwhelmed their anthropogenic counterparts in summer and dominated the daytime isoprene levels in spring and autumn. Even in winter, biogenic sources still contributed a non-negligible fraction of approximately 44% to daytime isoprene. Furthermore, the concentration contour of isoprene extrapolated from the data at 38 sites throughout the city revealed that high levels of biogenic isoprene were generally a widespread phenomenon in summer in the tropical–subtropical city. A three-dimensional plot of the isoprene/1,3-butadiene ratio, ambient temperatures and radiation flux showed a temperature threshold of biogenic isoprene emissions, beyond which the biogenic contribution began to increase exponentially with enhanced ambient temperature. However, when the ambient temperature was below the threshold, there was no or negligible biogenic contribution to the ambient isoprene, regardless of the strength of the radiation flux. The temperature threshold (approximately 17–21 °C) of isoprene emissions in the tropical–subtropical city was much higher than the thresholds in cities and areas at temperate latitudes, indicating that the adaptation of vegetation to different temperature zones via isoprene emission may be characteristic.