Air pollutant dispersion altered by urban-rural breeze and urban sprawl

2020 ◽  
Author(s):  
Yung-Chang Chen ◽  
Gong-Do Hwang ◽  
Wei-Nai Chen ◽  
C.-K. Charles Chou
Keyword(s):  
Large Eddy Simulation ◽  
Urban Sprawl ◽  
Air Pollutants ◽  
Pollutant Dispersion ◽  
Air Pollutant ◽  
Eddy Simulation ◽  
Synoptic Weather ◽  
Large Eddy ◽  
Air Pollutant Dispersion ◽  
Urban Rural

<p>Air pollution becomes a serious issue due to the population growing up and residential area sprawl in decades. Residential area is not only a major source of air pollutants but also an impact to generate an urban-rural thermal wind and to alter the dispersion of air pollutants. However, the urban-rural breeze caused by a metropolitan is not the only impact on the dispersion of air pollutants. Generally, a synoptic weather condition is the major impact to dominate how the air pollutant exactly diffuses. The most metropolitans are located in the coastal regions. Therefore, a naturally thermal wind, sea-land-breeze, plays also commonly an essential role to transfer the air pollutant. Additionally, topography and natural obstacle are unable to be ignored as an impact to obstruct flow streaming which brings the air pollutant away.</p><p>Overall, synoptic weather conditions, local sea-land-breeze patterns, and natural obstacles are three major natural impactors to influence air pollutant dispersion. The urban-rural-breeze pattern and the roughness of the urban area are regarded as the two anthropogenic factors to alter the large breeze system and thereby affecting the spreading pathway of the air pollutant. To analysis the interaction of above mentioned five impactors could be regarded as a comprehensive approach to consider how the air pollutant transfer from a metropolitan to air pollution suffering areas.</p><p>In this study, we apply either computational or measurement tools to consider the effects of metropolitan, Taichung, which is located in middle Taiwan, in the heat island effect and modification of the roughness to alter the natural breeze and also the dispersion of the air pollutant. Several intensive observation periods of 3-dimensional wind field network in boundary layer have been proposed as the evidences to discuss the impacts of urban sprawl on the breeze circulation in Taichung. Otherwise, a large-eddy-simulation model, Parallel-Large-Eddy-Simulation Model (PALM) is applied in the study initially to realize the influence of synoptic weather conditions and topography on air pollutant dispersion. Thereafter, the impacts of the heat fluxes and the roughness changing due to the urban sprawl are proposed in the study. Overall, the altering of metropolitan on the natural breeze is a slight but significant impact and could change the air pollutant dispersion.</p><p> </p><p>Key Words: Boundary Layer, Wind field, Large-Eddy-Simulation, PALM, Urban Sprawl, Heat Island Effect, Thermal Wind</p>

scholarly journals Sensitivity of local air quality to the interplay between small- and large-scale circulations: a large-eddy simulation study

2017 ◽  
Vol 17 (11) ◽  
pp. 7261-7276 ◽  
Author(s):  
Tobias Wolf-Grosse ◽  
Igor Esau ◽  
Joachim Reuder
Keyword(s):  
Air Pollution ◽  
Air Quality ◽  
Large Eddy Simulation ◽  
Air Pollutants ◽  
Large Scale ◽  
Wind Speeds ◽  
Street Level ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Air Pockets

Abstract. Street-level urban air pollution is a challenging concern for modern urban societies. Pollution dispersion models assume that the concentrations decrease monotonically with raising wind speed. This convenient assumption breaks down when applied to flows with local recirculations such as those found in topographically complex coastal areas. This study looks at a practically important and sufficiently common case of air pollution in a coastal valley city. Here, the observed concentrations are determined by the interaction between large-scale topographically forced and local-scale breeze-like recirculations. Analysis of a long observational dataset in Bergen, Norway, revealed that the most extreme cases of recurring wintertime air pollution episodes were accompanied by increased large-scale wind speeds above the valley. Contrary to the theoretical assumption and intuitive expectations, the maximum NO2 concentrations were not found for the lowest 10 m ERA-Interim wind speeds but in situations with wind speeds of 3 m s−1. To explain this phenomenon, we investigated empirical relationships between the large-scale forcing and the local wind and air quality parameters. We conducted 16 large-eddy simulation (LES) experiments with the Parallelised Large-Eddy Simulation Model (PALM) for atmospheric and oceanic flows. The LES accounted for the realistic relief and coastal configuration as well as for the large-scale forcing and local surface condition heterogeneity in Bergen. They revealed that emerging local breeze-like circulations strongly enhance the urban ventilation and dispersion of the air pollutants in situations with weak large-scale winds. Slightly stronger large-scale winds, however, can counteract these local recirculations, leading to enhanced surface air stagnation. Furthermore, this study looks at the concrete impact of the relative configuration of warmer water bodies in the city and the major transport corridor. We found that a relatively small local water body acted as a barrier for the horizontal transport of air pollutants from the largest street in the valley and along the valley bottom, transporting them vertically instead and hence diluting them. We found that the stable stratification accumulates the street-level pollution from the transport corridor in shallow air pockets near the surface. The polluted air pockets are transported by the local recirculations to other less polluted areas with only slow dilution. This combination of relatively long distance and complex transport paths together with weak dispersion is not sufficiently resolved in classical air pollution models. The findings have important implications for the air quality predictions over urban areas. Any prediction not resolving these, or similar local dynamic features, might not be able to correctly simulate the dispersion of pollutants in cities.

scholarly journals Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

2020 ◽  
Vol 10 (14) ◽  
pp. 4931
Author(s):  
Qianying Yi ◽  
David Janke ◽  
Lars Thormann ◽  
Guoqiang Zhang ◽  
Barbara Amon ◽  
...  
Keyword(s):  
Air Pollutants ◽  
Pollutant Dispersion ◽  
Air Pollutant ◽  
Emission Mitigation ◽  
Surrounding Environment ◽  
Air Pollutant Dispersion ◽  
Treatment Technologies ◽  
Downwind Side ◽  
Pollutant Distribution ◽  
Wake Zone

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e., 3.8 times building height), in which the emission concentration might be high. Additional air pollutant treatment technologies applied in this region might contribute to emission mitigation effectively. Furthermore, a wake zone with air recirculation was observed in this area. A smaller roof slope (i.e., 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance.

Large-Eddy Simulation of Reactive Pollutant Dispersion Over Street Canyons of Different Aspect Ratios

2014 ◽  
Author(s):  
T. Z. Du ◽  
Chun-Ho Liu ◽  
Y. B. Zhao
Keyword(s):  
Aspect Ratio ◽  
Large Eddy Simulation ◽  
Chemical Reactions ◽  
Pollutant Dispersion ◽  
Pollutant Removal ◽  
Street Canyons ◽  
Eddy Simulation ◽  
Aspect Ratios ◽  
Large Eddy ◽  
Reactive Pollutant

In urban areas, pollutants are emitted from vehicles then disperse from the ground level to the downstream urban canopy layer (UCL) under the effect of the prevailing wind. For a hypothetical urban area in the form of idealized street canyons, the building-height-to-street-width (aspect) ratio (AR) changes the ground roughness which in turn leads to different turbulent airflow features. Turbulence is considered an important factor for the removal of reactive pollutants by means of dispersion/dilution and chemical reactions. Three values of aspect ratio, covering most flow scenarios of urban street canyons, are employed in this study. The pollutant dispersion and reaction are calculated using large-eddy simulation (LES) with chemical reactions. Turbulence timescale and reaction timescale at every single point of the UCL domain are calculated to examine the pollutant removal. The characteristic mechanism of reactive pollutant dispersion over street canyons will be reported in the conference.

Large eddy simulation of pollutant dispersion in a naturally cross-ventilated model building: Comparison between sub-grid scale models

2019 ◽  
Vol 12 (5) ◽  
pp. 921-941 ◽  
Author(s):  
Farzad Bazdidi-Tehrani ◽  
Shahin Masoumi-Verki ◽  
Payam Gholamalipour ◽  
Mohsen Kiamansouri
Keyword(s):  
Large Eddy Simulation ◽  
Model Building ◽  
Pollutant Dispersion ◽  
Eddy Simulation ◽  
Scale Models ◽  
Large Eddy
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