Effects of Varying Wind Angles and Increasing Concentration on Air Pollutant Dispersion from Cooling Towers to Urban Area using Computational Fluid Dynamics Software

Managing and improving the air quality across urban areas can be achieved by studying the transport behaviour of air pollutants. In this work, the effects of varying wind angles and increasing concentration on air pollutant dispersion from cooling towers to urban area were investigated using computational fluid dynamics (CFD) software; OpenFOAM and the modified k-ω SST turbulence closure to acquire the steady-state flow field based on Reynolds Averaged Navier-Stokes Equation (RANS) approach. The results showed that varying the wind direction for the wind velocity profile from (1 0 0) to (Cos30 0 Sin30) and (Cos45 0 Sin45) affected the pollution dispersion across the urban area with the worst scenario being (1 0 0). In addition, reducing the diffusivity constant (Dt), thus increasing the pollution concentration, from 0.02 to 0.001 increased the pollution transport across the urban area considerably. This research shows the benefit of applying CFD approach toward managing the challenges of air pollution dispersion

CFD simulation of the dispersion of exhaust gases in a traffic-loaded street of Astana, Kazakhstan

The aim of this paper is to consider one of the most traffic-loaded regions of Astana city (Kazakhstan) and to determine the concentration of carbon-monoxide (CO) in the air during the peak hours. CFD analysis based on the SolidWorks-EFD platform was used to simulate the dispersion of contaminants given the estimated emission rates and weather conditions at the crossroad of Bogenbay Batyr and Zhenis Avenues in Astana. Turbulence prediction was based on k-ε model with wall functions. The governing equations were discretized using the finite volume method and a 2nd order spatial scheme. The mesh verification was based on 1% convergence criterion for a 50% of mesh density increment; air pressure near the wall of a selected building was chosen as the parameter to control the convergence. Numerical results are presented for prevailing conditions during all 4 seasons of the year, demonstrating that the highest levels of CO are recorded in summer and reach the values up to 11.2 ppm which are still lower than the maximum level admitted for humans. Nevertheless, obtained results show that Astana is gradually becoming a city that is likely to reach the critical levels of pollutants in the nearest future if control measures are not taken with enough anticipation. As for a future work, it is proposed to perform in-situ validation of specific scenarios to check and support the results obtained with CFD and to develop then specific policies for tackling the problem before it becomes evident

NASYP: Online expert tool on the control of major-accident hazards involving dangerous substances

NASYP is an online Geoportal tool being developed in cooperation with state and regional authorities to improve insufficient practices based on implementation of Directive nr. 2003/105/ES on the control of major-accident hazards involving dangerous substances. The tool is applicable for managing the permits, reporting and regular monitoring issues. Furthermore, it’s applicable for a risk assessment and a rapid management of disasters in the initial phase. There’re simple modeling tools included to simulate early stages of the contamination caused by disasters occurred to be used for decision making and effective use of emergency services. In this manner, there’re low atmospheric and surface water pollutions taken into account. For the study area, Liberec region was chosen covering the area of 3,163km2 and containing 533 potentially dangerous objects categorized accordingly to the Directive nr. 2003/105/ES. The model simulations are responding to daily hydrological and meteorological situation, a capability of automated updates from databases operated by the Czech Hydro Meteorological Institute, and communicate with databases of substances operated by the regional authorities. NASYP is suitable especially for the “N†class of the operators defined in the Directive, where because of smaller amounts of stored dangerous substances the safety measures and regular inspections are limited.Spatial data, geoportal, risk management, modelling, Research and Development/Tech Change/Emerging Technologies, Research Methods/ Statistical Methods, Risk and Uncertainty, GA, IN,

Modelação multiescala de qualidade do ar urbana para cidades mais saudáveis

Ambient air pollution is nowadays a serious public health problem worldwide, especially in urban areas due to high population density and intense anthropogenic activity. Among the main urban air pollution sources, the road traffic sector is one of the major concerns and the largest contributor to nitrogen dioxide (NO2) concentrations, though regional background chemical conditions must also be considered. In this context, the use of modelling tools is crucial to understand atmospheric and social dynamics in multiple scales, as well as to support in defining the best air quality improvement strategies. The main objective of this thesis is to develop and apply a multiscale modelling system able to simulate air quality and health impacts in cities. For this purpose, the modair4health multiscale air quality and health risk modelling system was developed and operationalized. It includes the online model WRF-Chem, which provides air quality and meteorological fields from regional to urban scales, and the Computational Fluid Dynamics (CFD) model VADIS, which uses the urban WRF-Chem outputs to calculate flows and dispersion of traffic emissions-related air pollutants in urban built-up areas. A health module, based on linear and non-linear World Health Organization approaches, was also integrated in modair4health to assess the health impacts resulting from air quality changes, and the overall health damage costs are calculated based on economic studies. The application and assessment of the modair4health system allowed to identify the most appropriate configurations and input data, which were used to apply the system over the case study testing air quality improvement scenarios. One of the busiest road traffic areas of the city of Coimbra (Fernão de Magalhães Avenue) in Portugal was selected as case study. The application considered a 4 domains setup: three nested domains (25, 5 and 1 km2 resolutions) for the WRF-Chem, and the 4th domain (4 m2 resolution) over the target local study area and NO2 for the VADIS. WRF-Chem was applied along the year 2015 and VADIS was simulating two particular periods: one week in winter and another one in summer. Short-term health impacts were estimated and the non-linear approach led to lower health outcomes that seem better adjusted to the local reality. Finally, to assess the modair4health capabilities for decision-making support, two traffic management scenarios were tested over the case study: replacement of 50% of the vehicle fleet below EURO 4 by electric vehicles (ELEC), and introduction of a Low Emission Zone (LEZ). Air quality and health positive impacts were higher for the ELEC scenario. This study represents a scientific advance in multiscale air quality and health modelling. The modair4health system can be easily adapted and applied to other simulation domains, providing urban air pollution levels and subsequent health impacts for different case studies and supporting the assessment of air pollution control policies.A poluição atmosférica é atualmente um sério problema mundial de saúde pública, especialmente em áreas urbanas, devido à elevada densidade populacional e intensa atividade antropogénica. O setor dos transportes rodoviários é uma das principais preocupações e o que mais contribui para concentrações de dióxido de azoto (NO2) na atmosfera, embora as condições químicas de fundo regional devam também ser consideradas. Neste contexto, a utilização de ferramentas de modelação é crucial para compreender a dinâmica atmosférica e humana a diferentes escalas, e apoiar na definição das melhores estratégias para melhoria da qualidade do ar (EMQA). Esta tese tem como objetivo principal o desenvolvimento e aplicação de um sistema de modelação multiescala que permita simular qualidade do ar e impactos na saúde em cidades. Para isso, foi desenvolvido e operacionalizado o sistema modair4health - multiscale air quality and health risk modelling. Este sistema inclui o modelo online WRF-Chem, que fornece campos meteorológicos e de qualidade do ar da escala regional à urbana, e o modelo CFD VADIS, que utiliza os resultados do WRF-Chem para calcular o impacto das emissões do tráfego rodoviário no escoamento e dispersão de poluentes em áreas urbanas. Para avaliar os impactos na saúde humana, foi também integrado um módulo baseado nas abordagens linear e não-linear da Organização Mundial de Saúde (OMS), e os custos são calculados com base em estudos económicos. A aplicação e avaliação do sistema modair4health permitiram identificar as configurações e dados de entrada mais apropriados, que foram posteriormente utilizados para testar EMQA sobre o caso de estudo, que corresponde a uma das áreas de maior tráfego rodoviário da cidade de Coimbra (Avenida Fernão de Magalhães). O WRF-Chem foi configurado com 3 domínios aninhados (resoluções de 25, 5 e 1 km2), simulados para o ano 2015; enquanto que para o VADIS, foi definido um quarto domínio (resolução de 4 m2) sobre o caso de estudo para simular concentrações de NO2 em dois períodos específicos: uma semana no inverno e outra no verão. Para quantificar os impactos na saúde, as duas abordagens da OMS foram aplicadas ao caso de estudo para avaliar efeitos a curto-prazo. A abordagem não-linear apresentou resultados de saúde mais baixos que aparentemente estão melhor ajustados à realidade local. Por fim, foram avaliadas as potencialidades do sistema no apoio à tomada de decisão, testando dois cenários de gestão do tráfego rodoviário: substituição de 50% da frota de veículos abaixo de EURO 4 por veículos elétricos (ELEC), e introdução de uma Zona de Emissões Reduzidas (LEZ). O cenário ELEC potencia melhorias mais significativas na qualidade do ar e saúde. Este estudo representa um avanço científico na modelação multiescala da qualidade do ar e saúde. O sistema modair4health pode ser facilmente adaptado e aplicado a outros casos de estudo para avaliar a qualidade do ar urbana e impactos na saúde, bem como para testar medidas de controlo da poluição atmosférica.Programa Doutoral em Ciências e Engenharia do Ambient

A new approach for roughness representation within urban dispersion models

The effects of green infrastructure on pollutant concentrations are greatly variable, essentially depending on the surrounding built-up environment and on local meteorological conditions. To simulate the effects of the presence of trees at urban scale, a reliable methodology is the Computational Fluid Dynamics (CFD) approach, however it needs high calculation costs. An alternative integral dispersion model is given by provided that a suitable parameterization for vegetation is included. In this work, we have developed and demonstrated a novel methodology, based on aerodynamic parameters, to include the aerodynamic effect of trees in an operational dispersion model, the ADMS-Urban. The aerodynamic parameters were derived using the morphometric method starting from open data containing information on buildings and trees. The new roughness parameter calculation method has produced the urban spatially varying roughness (USVR) and it was evaluated in different scenarios at the urban and neighborhood scale. The numerical outputs of the simulations were compared with observations from reference air quality stations collected within an ad-hoc intensive field campaign conducted in 2017 in the city of Bologna, Italy. The results of the comparison highlight that the introduction of the aerodynamic effects of buildings lead to great improvements in the performance of the model at both spatial scales and for the different study sites considered in this study. Conversely, the inclusion of trees in the calculation produces significant improvements only when conducting studies at high spatial resolution and for densely vegetated areas

Investigation of the Ventilation Rate around Different Urban Morphological Property Types: High Rise -Vs- Low Rise in Bangkok’s High Density Areas

As a consequence of city development and increased urbanization, Bangkok, the capital of Thailand, has experienced serious air pollution problems in high density areas over the past several decades, especially at pedestrian-level (at 1.5 meter level above ground) between groups of buildings in the city’s central block. As we all know that urban settings have a direct impact on the urban air flow. Lack of research because urban morphology (Greek morphé : shape) is too complicated to do air flow simulation. The objective of this study is to find the relationship between urban high-rise and low-rise morphology properties and urban air ventilation in high density areas of Inner Bangkok. The methodology involves an investigation using computer fluid dynamics (CFD) simulation. The results based on air change rate. Main findings of this paper are as follows; Urban high rise- high density areas has better ventilation rates than low rise- high density areas in all cases. The ventilation rate from high to low are as followings, 1) urban high rise- high density are block number 80, 17 and 65 and ACH is 26.23646, 25.63358, 12.77694 2) urban low-rise- high density are blocks 24, 30 and 26 and ACH is 11.72196, 11.19111, 5.769723, respectively. The conclusion of this research is the most influential variable factors is the height of the building. Blog orientation and open space in the city block

A Review on Atmospheric Dispersion System for Air Pollutants Integrated with GIS in Urban Environment

The objective of this article is to present comprehensive findings and analysis of studies performed on air pollutant dispersion in urban environments. It captures India’s rising environmental pollution due to urbanization, industrialization, and population growth. Dispersion of pollutants due to the wind in the lower Atmospheric Boundary Layer (ABL) is a major concern nowadays. The dispersion field around the buildings is a critical parameter to analyze and it primarily depends on the correct simulation of the wind flow structure. Therefore, studies performed on this in past years are being reviewed. Additionally, a brief review of different air dispersion models that are integrated with the Geographic Information System (GIS) has been studied in this article to assess the exposure. The results of these studies provide the urban air dispersion model aligning to three sub-models i.e., Emission, Weather Prediction, and Dispersion models. Various factors like wind speed, wind direction, cloud cover, traffic emission, disposal of waste, transportation, and others are considered. This study also captures the problems and risks being faced while creating a model, and its possible mitigation approaches

An operational method for assessing traffic-related air pollution in urban streets

Urban air quality has been a topic of major public concern and scientific research in recent years. Several theoretical and experimental studies have focused on the assessment of air quality within street canyons and other microenvironments (intersections, motorways, parking spaces, etc.), where population exposure to traffic-related pollutants is relatively high. The aim of this study was to develop a practical methodology for assessing traffic-related air pollution in urban streets, after testing available monitoring and modelling techniques. To meet this objective, a large amount of original air quality, meteorological and traffic data were collected during four intensive short-term and one long-term monitoring campaigns carried out in the region of Paris from December 1998 to December 2001. These campaigns covered three representative street canyon sites (Bd. Voltaire, Rue de Rennes, Av. Leclerc - PI. Basch) as well as a motorway service station (RN10 petrol station). Passive and active monitoring techniques were used to sample a wide range of inorganic (CO, NO X and Os) and organic gases (benzene, toluene, xylene, ethylbenzene, formaldehyde, acetaldehyde, etc.) at different heights and distances from the kerb. Indicative background measurements were also taken during the same sampling periods. Furthermore, relevant meteorological (synoptic and local) and traffic information was obtained on each site. The analysis of the data gave insights into the dispersion and transformation processes taking place within the streets. Channelling effects induced by parallel to the road axis winds gave rise to relatively high kerbside pollution levels. On the other hand, perpendicular synoptic winds generated air vortices within the canyons, which resulted in steep crossroad concentration gradients. In that case, higher pollution levels were observed on the leeward than on the windward side of the streets. A significant reduction of concentrations with height above the ground was also observed within two of the street canyons (Bd. Voltaire and Av. Leclerc). In all cases, roadside concentrations were several times higher than the corresponding urban background values. This spatial variability indicates a strong transport effect on the pollutant distribution within urban canyons, caused by the synoptic wind and influenced by the geometry of the street. That may have serious implications in terms of population exposure and compliance with air quality legislation. In this context, the siting of permanent monitoring equipment becomes crucial. A relationship between CO and benzene as well as an exponential expression linking pollutant concentrations at different heights within the canyons were empirically deduced. Five dispersion models of different levels of complexity (STREET-SRI, OSPM, AEOLIUS, CAR-International, and CALINE4) were used to calculate CO and benzene concentrations at the campaign sites. The Computational Fluid Dynamic code PHOENICS was also tested for one location. The comparison between observed and predicted values revealed the advantages and drawbacks of each model in association with the configuration of the street and the meteorological conditions. Furthermore, a sensitivity and uncertainty analysis involving three of the available models (STREET-SRI, OSPM and AEOLIUS) was carried out. OSPM was slightly modified in order to allow user access to certain internally coded parameters. An operational method combining multi-site sampling and dispersion modelling was finally proposed for assessing air quality in urban streets, taking into account the pronounced spatial and temporal variability of traffic-related air pollution, the modelling uncertainty, the practical constraints related to measurements and models, and the needs of decision makers. This methodology may find wider application in air quality management, urban and transport planning, and population exposure studies