| 1. |
- Buccoliere, Riccardo, et al.
(author)
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City breathability and its link to pollutant concentration distribution within urban-like geometries
- 2010
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In: Atmospheric Environment. - : Elsevier. - 1352-2310 .- 1873-2844. ; 44:15, s. 1894-1903
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Journal article (peer-reviewed)abstract
- This paper is devoted to the study of pollutant concentration distribution within urban-like geometries. By applying efficiency concepts originally developed for indoor environments, the term ventilation is used as a measure of city “breathability”. It can be applied to analyse pollutant removal within a city in operational contexts. This implies the evaluation of the bulk flow balance over the city and of the mean age of air. The influence of building packing density on flow and pollutant removal is, therefore, evaluated using those quantities. Idealized cities of regular cubical buildings were created with packing density ranging from 6.25% to 69% to represent configurations from urban sprawl to compact cities. The relative simplicity of these arrangements allowed us to apply the Computational Fluid Dynamics (CFD) flow and dispersion simulations using the standard k– turbulence model. Results show that city breathability within the urban canopy layer is strongly dependent from the building packing density. At the lower packing densities, the city responds to the wind as an agglomeration of obstacles, at larger densities (from about 44%) the city itself responds as a single obstacle. With the exception of the lowest packing density, airflow enters the array through lateral sides and leaves throughout the street top and flow out downstream. The air entering through lateral sides increases with increasing packing density.At the street top of the windward side of compact building configurations, a large upward flow is observed. This vertical transport reduces over short distance to turn into a downward flow further downstream of the building array. These findings suggest a practical way of identifying city breathability. Even though the application of these results to real scenarios require further analyses the paper illustrates a practical framework to be adopted in the assessment of the optimum neighbourhood building layout to minimize pollution levels.
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| 2. |
- Burman, Jan, et al.
(author)
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Issues when linking computational fluid dynamics for urban modeling to toxic load models : The need for further research
- 2015
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 104, s. 112-124
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Journal article (peer-reviewed)abstract
- In order to predict casualties caused by chemical hazards in densely populated areas, state-of-the-art Computational Fluid Dynamic (CFD) techniques could be utilized together with toxic load models. In the current study, simulations of consequences of hypothetical releases of toxic gas in a city center are presented and discussed. CFD models that reproduce flow statistics would be most appropriate for this purpose since it could be expected that they will more realistically represent the environment. However, since concentration-peaks in the ever-present spatiotemporal fluctuations of airborne chemicals contribute so much to the toxic load, it is shown that straight-forward direct linking of a CFD model to a toxic load model is not a suitable approach for predicting consequences of a toxic release. Furthermore, it is demonstrated that the use of different turbulence models leads to different casualty assessments. Obviously, there is an urgent need to establish widely accepted methods, ideally with known uncertainty measures. Thus, further research in this area is of great importance.
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| 3. |
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| 4. |
- Edvardsson, Karin, et al.
(author)
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Monitoring of dust emission on gravel roads : Development of a mobile methodology and examination of horizontal diffusion
- 2009
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 43:4, s. 889-896
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Journal article (peer-reviewed)abstract
- Traffic-generated fugitive dust on gravel roads impairs visibility and deposits on the adjacent environment. Particulate matter smaller than 10 mu m in diameter (PM10) is also associated with human health problems. Dust emission strength depends on the composition of granular material, road moisture, relative humidity, local Climate (precipitation, wind velocity, etc.), and vehicle characteristics. The objectives of this study Were to develop a reliable and rapid mobile methodology to measure dust concentrations on gravel roads, evaluate the precision and repeatability of the methodology and correspondence with the currently used Visual assessment technique. Downwind horizontal diffusion was studied to evaluate the risk of exceeding the maximum allowed particulate matter concentration in ambient air near gravel roads according to European Council Directive [European Council Directive 1999/30/EC of 22 April 1999 relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. Official Journal of the European Communities. L163/41.]. A TSI DustTrak Aerosol Monitor was mounted on an estate car travelling along test sections treated with various dust suppressants. Measured PM10 concentrations were compared to Visual assessments performed at the same time. Airborne particles were collected in filters Mounted behind the vehicle to compare the whole dust fraction with the PM10 concentration. For measuring the horizontal diffusion, DustTraks were placed at Various distances downwind of a dusty road section. The mobile methodology was vehicle and speed dependent but not driver dependent with pre-specified driving behaviours. A high linear correlation between PM10 of different vehicles makes relative measurements of dust concentrations possible. The methodology gives continuous data series, mobility, and easy handling and provides fast, reliable and inexpensive measurements for estimating road conditions to make road maintenance more efficient. Good correlations between measured PM10-values, visually assessed dust generation and dust collected in filters were obtained. PM10 seems to be correlated to the whole dust fraction that impairs visibility on gravel roads. A decay in PM10 concentration as a function of distance from the road was observed. Measured particles principally did not travel further than 45 m from the road. The risk of exceeding the PM10 concentration stated in the EC-directive seems small.
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| 5. |
- Hang, Jian, et al.
(author)
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Effect of urban morphology on wind condition in idealized city models
- 2009
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 43:4, s. 869-878
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Journal article (peer-reviewed)abstract
- Wind conditions in urban environments are important for a number Of reasons. They can serve to out of the urban environment and to moderate urban microclimatic conditions if transport air Pollutants satisfactory, yet can compromise pedestrian comfort and safety if not. We aim to study experimentally and numerically the effects of urban morphology (e.g., overall city form (skyline), street orientation, and street configuration) on wind conditions in cities. This report considers our initial investigations of two idealized city forms that are coincidentally similar to ancient Roman cities that were organized On One OF two primary streets - a main north-south street, the cardus maximus, and a secondary east-west street, the decumanus maximus - and contained within a well-defined perimeter. We first consider round and square city models with one main street set parallel to the approaching wind and a secondary street producing an intersection at city centre. Not Surprisingly, wind conditions in the two city models are dissimilar due to their shape differences. We then consider a long rectangular city model with a fully developed steady flow region along the main street. If the main street of the round city model is narrow, the parallel approaching wind cannot blow through the entire street and a penetrating inflow exists at the leeward opening. For the Found city model with two crossing streets, a slightly non-parallel wind to the main Street generates a stronger wind level in the entire street volume, Crown.
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| 6. |
- Hang, Jian, et al.
(author)
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Pollutant dispersion in idealized city models with different urban morphologies
- 2009
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 43:38, s. 6011-6025
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Journal article (peer-reviewed)abstract
- The mechanism of pollutant dispersion in idealized city models is investigated numerically by the introduction of a uniformly distributed pollutant source at street pedestrian level. We first study three short city forms with a single main street or two crossing streets, characterized by street length/street height ratios of L/H = 6 or 7 and a street height/street width ratio of H/W = 1, including a sharp-edged round city model, a smooth-edged round city model, and a sharp-edged square city model. For short city models with a single street and a parallel approaching wind, pollutant dilution mainly depends on the horizontal flow rate which decreases along the street. This decreasing rate is smallest for the smooth-edged round city model, which results in the lowest street concentrations. For city models with two crossing streets and the approaching wind parallel to the main street. the differences in overall city form result in different dispersion processes. For a sharp-edged round city model with two crossing streets, an approaching wind slightly non-parallel to the main street generates a lower pollutant concentration in the entire street volume. We also studied a sharp-edged round city model with one narrow street (L/H = 6: H/W = 6.7), finding that the uniformly distributed pollutants are transported from two street entries to the city centre, and are then removed out across the street roof. In contrast to the short city models we studied a single-street sharp-edged long rectangular city model (L/H = 21.7; H/W = 1) in which the horizontal flow rate remained nearly constant in a region far from the two entries. Within this region the turbulence across the street roof contributed more to the pollutant removal than vertical mean flows.
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| 7. |
- Samie, Farid, et al.
(author)
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Atmospheric corrosion effects of HNO3—Influence of concentration and air velocity on laboratory-exposed copper
- 2006
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 40:20, s. 3631-3639
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Journal article (peer-reviewed)abstract
- `A recently developed experimental set-up has been used to explore the atmospheric corrosion effects of nitric acid (HNO3) on copper, in particular the influence of concentration and air velocity. Characterization and quantification of the corrosion products on exposed samples were performed with Fourier transform infrared (FT-IR) microspectrocscopy, ion chromatography, X-ray diffraction (XRD), micro-balance and microscopy. At low air velocity (0.03 cm s(-1)) HNO3 deposition and weight gain of copper increased linearly with concentration Lip to 400 mu g m(-3) or 156 ppb. The influence of air velocity on corrosion of copper was tested within the range of 0.03-35.4 cm s(-1). Although the air velocity in this study was significantly lower than typical outdoor wind values, a high HNO3 concentration of the air velocity of 35.4 cm s(-1) resulted in a relatively high deposition velocity (V-d) of 0.9 cm s(-1) on the metal surface and 1.2 cm s(-1) on an ideal absorbent, which would imply a limiting deposition velocity on the copper surface (V-d,V-surf) of 3.6 cm s(-1). Results obtained in this study emphasize the importance for future research on the corrosion effects of HNO3 on materials as very little has so far been done in this field.
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| 8. |
- Samie, Farid, et al.
(author)
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Atmospheric corrosion effects of HNO3—method development and results on laboratory-exposed copper
- 2005
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 39:38, s. 7362-7373
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Journal article (peer-reviewed)abstract
- The effects of the atmospheric pollutant nitric acid (HNO3) on materials compared to other corrosive gases, e.g. sulphur dioxide (SO2), nitrogen dioxide (NO2) or ozone (O-3), have so far received little or no attention. The high sticking coefficient of HNO3 makes this gas one of the most difficult gases to work with. A new apparatus has now successfully been developed for studying the atmospheric corrosion effects of HNO3 Oil materials. HNO3 concentration measurements up to 1080 mu g m(-3) (420 ppb) were performed by dissolving the gas in water and analysing the nitrate concentration with ion chromatography (IC). Small changes in relative humidity (RH) largely affect the concentration of this pollutant in the exposure chamber and the high sticking coefficient of this gas on copper and quartz glass has been shown. The quartz glass surface, however, became saturated after a certain time of exposure and at 82% RH, the number of monolayers on the surface was estimated to be 10-13. Initial results of copper samples exposed to HNO3 show that at 63% RH and 25 degrees C, the deposition of HNO3 on copper is slightly lower than on a perfect absorber. The loss of HNO3 during exposure of the samples showed good agreement with the amount of nitrates dissolved from surfaces of the samples after exposure. FT-I R, XRD and IC analyses of copper exposed to HNO3 and mass loss and mass gain analyses confirmed cuprite (Cu2O) and the basic copper nitrate, gerhardtite, as the main corrosion products. Deposition, as well as the corrosion effect, of HNO3 on copper appeared to be greater than that of any of the other above-mentioned pollutants.
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| 9. |
- Samie, Farid, et al.
(author)
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Atomospheric corrosion effects on HNO3 - comparison of laboratory exposed copper, cinc and carbon steel
- 2007
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 41:23, s. 4888-4896
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Journal article (peer-reviewed)abstract
- The effect of HNO3 on the atmospheric corrosion of copper has been investigated at varied temperature (15-35 degrees C) and relative humidity (0-85% RH). Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) confirmed the existence of cuprite and gerhardtite as the two main corrosion products on the exposed copper surface. For determination of the corrosion rate and for estimation of the deposition velocity (V-d) of HNO3 on copper, gravimetry and ion chromatography has been employed. Temperature had a low effect on the corrosion of copper. A minor decrease in the mass gain was observed as the temperature was increased to 35 degrees C, possibly as an effect of lower amount of cuprite due to a thinner adlayer on the metal surface at 35 degrees C. The V-d of HNO3 on copper, however, was unaffected by temperature. The corrosion rate and V-d of HNO3 on copper was the lowest at 0% RH, i. e. dry condition, and increased considerably when changing to 40% RH. A maximum was reached at 65% RH and the mass gain remained constant when the RH was increased to 85% RH. The V-d of HNO3 on copper at >= 65% RH, 25 degrees C and 0.03 cm s(-1) air velocity was as high as 0.15 +/- 0.03 cm s(-1) to be compared with the value obtained for an ideal absorbent, 0.19 +/- 0.02 cm s(-1). At sub-ppm levels of HN03, the corrosion rate of copper decreased after 14 d and the growth of the oxide levelled off after 7 d of exposure
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| 10. |
- Samie, Farid, et al.
(author)
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Atomospheric corrosion effects on HNO3 - influence of temperature and relative humidity on laboratory exposed copper
- 2007
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 41:1, s. 1374-1382
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Journal article (peer-reviewed)abstract
- The effect of HNO3 on the atmospheric corrosion of copper has been investigated at varied temperature (15-35 degrees C) and relative humidity (0-85% RH). Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) confirmed the existence of cuprite and gerhardtite as the two main corrosion products on the exposed copper surface. For determination of the corrosion rate and for estimation of the deposition velocity (V-d) of HNO3 on copper, gravimetry and ion chromatography has been employed. Temperature had a low effect on the corrosion of copper. A minor decrease in the mass gain was observed as the temperature was increased to 35 degrees C, possibly as an effect of lower amount of cuprite due to a thinner adlayer on the metal surface at 35 degrees C. The V-d of HNO3 on copper, however, was unaffected by temperature. The corrosion rate and V-d of HNO3 on copper was the lowest at 0% RH, i. e. dry condition, and increased considerably when changing to 40% RH. A maximum was reached at 65% RH and the mass gain remained constant when the RH was increased to 85% RH. The V-d of HNO3 on copper at >= 65% RH, 25 degrees C and 0.03 cm s(-1) air velocity was as high as 0.15 +/- 0.03 cm s(-1) to be compared with the value obtained for an ideal absorbent, 0.19 +/- 0.02 cm s(-1). At sub-ppm levels of HN03, the corrosion rate of copper decreased after 14 d and the growth of the oxide levelled off after 7 d of exposure.
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