Street Air Research Articles

Integrated impacts of surrounding building density and gap permeability on pollutant dispersion in four-way street networks.

Gaps between buildings facing the streets can effectively accelerate the natural removal of pollutants in street canyons by enhancing ventilation and diffusion processes. This removal process is closely related to gap permeability (Pg, ratio of gap width to street length) and building density (λn) surrounding the streets. However, the integrated effects of these two parameters on pollutant dispersion remain unclear, because of the limited computational resources and the difficulty of traditional modeling methods to discrete the numerous buildings. Numerical simulations coupled with the porous media approach are performed for this purpose. Results indicate that for isolated streets surrounded by empty land (λn = 0), the high-speed airflow through the gaps causes significant flushing effects on pollutants in the street, and thus larger Pg induces better street air quality than the case without gaps (Pg = 0). Conversely, when the streets are surrounded by buildings (λn ≠ 0), the air quality is good for both smaller Pg = 0 and larger Pg = 52 %, and the worst case occurs in Pg = 24 %. Moreover, because of the blocking effect of surrounding buildings, the percentage of pollutant removal by the gaps decreases with increasing λn, which can reach up to 50 % for λn = 0, decreasing to 30 % for medium density (λn = 0.22). Notably, for high density (λn = 0.44), only when Pg > 52 % the pollutant concentration can be reduced compared to Pg = 0. The present findings can serve as principles for determining appropriate building gap layouts at different building densities, thereby improving the urban air quality more effectively.

An experimental study of the effects of using cool materials at different building heights on the indoor and outdoor environment

Four building arrays, each comprising 25 building models, were utilized to investigate the effects of cool materials on building surface temperatures, indoor temperatures, and street microclimates in Guangzhou, China. The experiments are divided into three groups. The first group of the experimental models is used to investigate the cooling effect of the roof using cool materials on the roof surface and indoor environment. The results show that using cool materials on roofs can significantly reduce roof surface and indoor temperatures of the top floor by 13.5 °C and 3.9 °C at noon under an average global solar radiation (GSR) of 727 W/m2. The second group of experiments included four arrays: one control group without cool materials and three other arrays applying cool materials on the third, second, and first floors, respectively. Using cool materials on the façades of the third, second, and first floors reduced the indoor temperature by an average of 1.9 °C, 0.8 °C, and 0.5 °C (average GSR = 404 W/m2), respectively. As a result, higher floors receive more solar radiation, and cool materials show better cooling capacity. The third group is used to investigate the effect on street air temperatures when cool materials are used on all building façades. Overall, the effect of cool materials on the street air temperature is very small, with a maximum reduction of only 0.2 °C in the street air temperature.

The Impact of the Air-Conditioning Systems on the Urban Microclimate of Beirut City

The urban heat island consists of the increase in the ambient temperature in urban areas with respect to their rural surroundings, due to artificial modifications of the natural land cover. As a result, significant increase in the demand on cooling loads occurs in cities during summer, inducing more energy consumption in buildings. Furthermore, air-conditioning systems release anthropogenic waste heat to outdoor intensifying the urban heat island. Therefore, an interactive relation exists between the heat islands formation and the cooling systems as well as mutual impacts. Hence, the contribution of the air-conditioning systems to the urban heat island is assessed through an appropriate numerical simulation for Beirut city. It is found that the intensive use of air conditioning systems in Beirut during summer could rise the street air temperature of about 0.8°C in the daytime and up to 4.7°C in the nighttime.

Quantifying cooling benefits of cool roofs and walls applied in building clusters by scaled outdoor experiments

Cool coating on building surfaces is a promising technique for cooling cities in summer. However, field measurements considering building clusters coupling cool roofs and/or cool vertical walls are rare. We conducted new-type scaled outdoor experiments in a suburb of Guangzhou, China (23°1′N, 113°25′E) to quantify the impacts of various reflective coatings on overall urban albedo, roof and wall temperature (Troof and Twall), and street air temperature (Tair) in three-dimensional high-rise building clusters. These experiments involved (a) high/low reflective roofs with a plan area index λp=0.25/0.44 (street width W = 0.5 m/0.25 m, building height H = 1.2 m) and (b) different cool coating modes with white coating as λp=0.44, i.e., roof coating (R-type), wall coating (W-type), both roof and wall coating (RW-type). As λp=0.25/0.44, cool roofs increase daytime average albedo αa from 0.16/0.19 to 0.26/0.34 reducing Troof by ∼8.0 °C on average for both urban densities. When λp=0.44, the RW-type increases αa (∼0.18–0.20) by 138.9%, significantly more than the R-type (88.9%) and W-type (20.0%). However, Twall (z/H < 0.5) is minimally affected by all three coating modes and Tair remains largely unchanged. This study provides valuable insights into the efficacy of cool coatings in urban environments and offers high-quality experimental data for validating related numerical simulations.

Numerical investigation of solar impacts on canyon vortices and its dynamical generation mechanism

With the booming concerns over urban heat island phenomenon, impacts of solar radiation on flow and temperature in street canyons have been revealed by some experimental and numerical investigations, where amplified single-vortex structures are found in shallow canyons in high-Re scenarios (Re ~ 107). Canyon surfaces are heated mainly by absorbing solar radiation, and street air is warmed primarily through thermal exchange with canyon surfaces. Most previous publications focus on simulations of flow regimes, pollutant dispersion and thermal comfort in canyon's microenvironments, while dynamical investigations on vortex genesis are vague and mostly emphasize analysis of dimensionless numbers. This research will theoretically explore the impacts of solar radiation on vortex genesis over idealized two-dimensional urban canyons by coupling k-ε turbulence model and P-1 radiation model. A possible dynamical mechanism of canyon-vortex generation will be introduced based on baroclinic vortex generation theory. Result shows that, the activity of wind shear (momentum field) and buoyancy imbalance (thermal field) are mutual, and their activation have a prerequisite of low vertical wind-speed environment. Signal of disturbance wind shear is critical for main vortex maintenance and the genesis of secondary or corner vortices. This mechanism has been proved both by our steady- and unsteady-RANS simulation.

ASSESSMENT OF STREET AIR POLLUTION THROUGH OSPM MODEL IN LAHORE, PAKISTAN

Traffic emissions are one of the main contributors in worsening the air quality of developing countries like Pakistan. The current research work is an effort to find out emission factor of different classes of vehicles as well as to model the certain air pollutants level on five different main streets of Lahore, Pakistan. The Town Hall air quality monitoring station at Mall road is taken as background station. The data of street configuration, background urban air pollution, meteorological conditions, diurnal traffic count and emission factor of vehicles was calculated to model the street air pollution. Operational Street Pollution Model (OSPM) was used to model the street pollutants. PM2.5 levels exceed National Environmental Quality Standards (NEQS) during all months of calendar year, while SO2 and NO2 exceed NEQS during entrance of heavy traffic at night in the city. Diesel vehicles have high SO2, NOx, PM2.5 and PM10 emission factors; while gasoline vehicles have high CO emission factors. Industrial region has relatively high level of SO2 emissions; while roadside have relatively high level of CO emissions. A significant correlation (rvalue > 0.5) was observed between modeled and observed results for all the streets for the NOx, SO2 and CO levels, except for NOx level at Gulberg (r-value= 0.42). The better modeling results have been observed for those streets which are relatively polluted spots and are close to the background station.

Analytical and numerical study on transient urban street air warming induced by anthropogenic heat emission

Anthropogenic heat emission is an important factor for street air warming. In this study, the transient street air warming process caused by anthropogenic heat is investigated by both the analytical model and Large-Eddy Simulation (LES). A new analytical model is developed based on the empirical exchange velocity modelling and heat exchange rate estimation. In the model, the buoyancy effect is included by introducing a buoyancy coefficient. With the new analytical model, both transient time and steady-state street air temperature increment (Θc) can be easily estimated in urban areas. This new model is calibrated and validated by cross-comparing with LES results. A good agreement is found between the results after including the buoyancy coefficient into the analytical model. Modelling results indicate that Θccould be limited because the buoyancy effect increases the exchange velocity between the urban canopy layer and overlying atmosphere. Furthermore, the buoyancy is also important to the transient air exchange process. A transformation of the urban canopy layer flow structure is found in the transient period, suggesting a large scale turbulence structure induced by anthropogenic heat. Lastly, the air temperature increment in the residential areas of Singapore is estimated with GIS (Geography Information System) tool to show the application of the analytical model in practice.

Street protests and air pollution in Hong Kong

June 2019 saw large-scale street protests in Hong Kong that impeded traffic flow along streets in areas around to the Legislative Council building. These had the potential to reduce overall air pollutant emissions from traffic and lower their concentrations. Two roadside monitoring stations relatively close to the Legislative Council reveal that measured concentrations of nitrogen dioxide declined during the protests compared with measurements from other sites by at least 50% on many occasions. There were only subtle changes in particulate loads and no evidence of any reduction in carbon monoxide concentrations. Pedestrianisation and bus route rationalisation are often seen as methods to reduce exposure in congested areas, but the observations here suggest that the substantial improvements in the nitrogen dioxide levels might not be matched by improvements in other pollutants. Plans for changes to street layouts to improve air quality need careful investigation before they are implemented.

Opredelenie tverdykh primesey v vozdukhe

At present the pollution of atmospheric air is one of the major problems of the modern environmental situation in the world. The concentration of solid particles is often used as an indicator of the air pollution level. One of the methods of monitoring various admixtures in air is the accumulation of their ions in water. To this aim, deionized water is saturated with street air during 2 hours at 2 l/min flow rate. The experiment was conducted on October 27, 2019. Using the site https://earth.nullschool.net, the wind direction was determined, namely from the city of Monchegorsk, which is situated to north of the place of the experiment. The results of iron tests were obtained using the Shimadzu atomic absorption spectrophotometer and were 9 mg/m3. In the future, the comparative experiments are planned as well as the use of various adsorbents.

The Heating System of Agricultural Facilities Using Excess Heat Power Transformers

In power transformers, energy losses in the form of heat are about 2 percent of their rated power, and in transformers of large power centers reach hundreds of kilowatts. Heat is dissipated into the environment and heats the street air. Therefore, there is a need to consume this thermal energy as a source of heat supply to nearby facilities. (Research purpose) To develop methods and means of using excess heat of power transformers with improvement of their cooling system design. (Materials and methods) The authors applied following methods: analysis, synthesis, comparison, monographic, mathematical and others. They analyzed various methods for consuming excess heat from power transformers. They identified suitable heat supply sources among power transformers and potential heat consumers. The authors studied the reasons for the formation of excess heat in power transformers and found ways to conserve this heat to increase the efficiency of its selection. (Results and discussion) The authors developed an improved power transformer cooling system design to combine the functions of voltage transformation and electric heating. They conducted experiments to verify the effectiveness of decisions made. A feasibility study was carried out on the implementation of the developed system using the example of the TMG-1000/10/0.4 power transformer. (Conclusions) The authors got a new way to use the excess heat of power transformers to heat the AIC facilities. It was determined that the improved design of the power transformer and its cooling system using the developed solutions made it possible to maximize the amount of heat taken off without quality loss of voltage transformation.

Assessment of bioaerosols in indoor air of glasshouses located in a botanical garden

Plants, like humans and pets, can be regarded as significant sources of airborne bacteria and fungi in different indoor environments. Especially abundant collection of distinct vegetation can be found in glasshouses of botanical gardens. However, bioaerosol concentrations, particle size distribution and species composition have not been studied in these facilities. Hence, the indoor air of glasshouses in a botanical garden was sampled with regard to bioaerosol quantitative and qualitative characteristics in comparison to those of the garden outdoor and adjacent street air. Both in winter and summer sampling times, higher concentrations of airborne bacteria and fungi were ascertained in the glasshouses compared to those detected at the outdoor sites. The respirable fraction of microorganisms prevailed, showing distinct contribution of fine bioaerosol particles in size below 4.7 μm (≤2.1 μm for bacteria in winter), within the indoor air. Distinct plant or soil derived bacteria and fungi, with the presence of potentially hazardous and allergenic agents, were identified in this environment. The results indicate that different plants, assembled in the closed area as the garden glasshouses, significantly affect the indoor air quality. The garden workers and visitors should be aware of higher exposure to bioaerosols in these facilities than in the outdoor air.

The Street Air Warming Phenomenon in a High-Rise Compact City

The street thermal environment is important for thermal comfort, urban climate and pollutant dispersion. A 24-h vehicle traverse study was conducted over the Kowloon Peninsula of Hong Kong in summer, with each measurement period consisting of 2–3 full days. The data covered a total of 158 loops in 198 h along the route on sunny days. The measured data were averaged by three methods (direct average, FFT filter and interpolated by the piecewise cubic Hermite interpolation). The average street air temperatures were found to be 1–3 °C higher than those recorded at nearby fixed weather stations. The street warming phenomenon observed in the study has substantial implications as usually urban heat island (UHI) intensity is estimated from measurement at fixed weather stations, and therefore the UHI intensity in the built areas of the city may have been underestimated. This significant difference is of interest for studies on outdoor air temperature, thermal comfort, urban environment and pollutant dispersion. The differences were simulated by an improved one-dimensional temperature model (ZERO-CAT) using different urban morphology parameters. The model can correct the underestimation of street air temperature. Further sensitivity studies show that the building arrangement in the daytime and nighttime plays different roles for air temperature in the street. City designers can choose different parameters based on their purpose.

Impact of indoor-outdoor temperature differences on dispersion of gaseous pollutant and particles in idealized street canyons with and without viaduct settings

Computational fluid dynamics simulations were performed to investigate flow and pollutant dispersion in a 2D street canyon of aspect ratio H/W = 1. Different from other works, the combination of the presence of viaduct and indoor-outdoor temperature differences ΔT is investigated for different approaching wind velocities. For larger wind velocity (2 m/s, Froude number Fr~3.06–12.24) the typical clockwise vortex leads to higher concentrations of both gas and small particles at the leeward side of the street and in the leeward-side rooms; the vortex is enhanced under large ΔT (20 K) improving the dispersion of pollutants. For smaller velocity (0.5 m/s, Fr~0.19–0.77) the appearance of an anti-clockwise vortex leads to a strong accumulation of gas and particles at the windward side and in the windward-side rooms under low ΔT (5 K); increasing the ΔT raises the dispersion of pollutants with consequent lower concentrations in the rooms (up to an average of 67% with respect to the isothermal case for gaseous pollutants), but accumulation close to the ground level at both windward-side and leeward-side rooms. In the presence of viaduct, together with the main vortex above the viaduct which causes concentrations increasing from low-level to high-level leeward-side rooms, two vortices are generated below it. Still ΔT = 20 K improves the dispersion of pollutants, leading up to a maximum of about 30% lower gaseous concentrations in the rooms. In general, lower concentrations of gas and particles are found for larger velocity, indicating that the mechanical turbulence dominates over the buoyancy effects, which become crucial for smaller velocity. This study confirms previous findings that viaducts may improve pollutant dispersion under large velocity if only one viaduct-level pollutant source exists and indoor-outdoor ΔT conditions can mitigate street air pollution.

Origin of polycyclic aromatic hydrocarbons and other organic pollutants in the air particles of subway stations in Barcelona

Underground subways transport large numbers of citizens in big cities, which must breathe air with limited ventilation. These atmospheric conditions may enhance the concentration of air pollutants from both outdoor and indoor air. The influence of ventilation conditions and maintenance activities on the concentrations of air pollutants have been studied. Particulate matter with aerodynamic diameter smaller than 2.5 μm (PM2.5) in indoor air was sampled in ten platforms of nine subway stations of the metropolitan area of Barcelona in 2015 and 2016. These particles were analyzed for polycyclic aromatic hydrocarbons (PAH) and organic tracer compounds. The concentrations of PAH were in the range of the street air levels with higher PAH values in the colder period. No influence of nighttime maintenance activities was observed on the platform air quality during daytime. Source apportionment analysis using the concentrations of hopanes, nicotine and levoglucosan as molecular tracer compounds showed that 75% of the detected PAH at the platforms have an outdoor PM origin. The modern subway stations, with advanced ventilation and platform screen doors that separate the subway system from the platform, showed lowest PAH and PM concentrations.

How we got People thinking about Walking in Prague ( elevator pitch )

Background At the beginning of the last year we started a new campaign focused on prospective city walkers – people who are in shape to walk and whose usual destinations are, as a rule, within their walking range. Aim The aim of the campaign was to emphasise the potential of walking and its possibilities in the city environment. And, consequently, to leverage those mentioned above to switch to walking as a daily means of transport. Method The campaign culminated in September 2016 during European Mobility Week, when a new Map for Walkers of Prague was released. Its aim was to point out the nice (green, calm, interesting) parts of the city and let people know that, actually, the choice was theirs – where to go, how to make their ordinary day better by enjoying every minute of walking. Results The map got quite popular by a single thing we ourselves did not regard as particularly important in the beginning – marking out heavily air-polluted streets on the basis of street traffic data. By a field survey we also proved that there is a strong connection between an actual level of street traffic and air pollution on the site. Conclusions Sometimes the trick is to show people that even the city offers various options in transport – and that some of them are more enjoyable and healthy then driving the cars in morning traffic jams and continually making the situation worse for everybody.

Modeling green wall interactions with street canyons for building energy simulation in urban context

A hygrothermal model of green walls and a model of mass flows in street canyons have been proposed and implemented in a building simulation program (TRNSYS). The coupled models allow the study of the hygrothermal interaction of green walls at the interface of the detailed building model and the urban microclimate of the street. Its use highlights the effects on both urban microclimate and buildings energy loads, especially in the summer period. While reducing anthropogenic heat release, green walls set up on west or east façades mitigate the street air temperature and reduce building cooling loads depending on streets’ aspect ratio. Some of the canyon model parameters were calibrated through numerical comparison with experimental data on a reduced scale mockup. This mockup has been designed specifically to assess the green walls hygrothermal impact and to evaluate the developed numerical tools. This experimental calibration made simulating the green walls interactions with street canyons of different aspect ratios possible. The experimental and numerical results obtained with green façades underline the advantage of this modeling approach for the design of passive cooling for buildings and mitigation of excessive thermal conditions within street canyons in dense cities in warm climates.

Integrated Effects of Street Layouts and Wall Heating on Vehicular Pollutant Dispersion and their Reentry Toward Downstream Canyons

ABSTRACTVehicle emission is becoming one of the major sources of gaseous pollutants and aerosol particles in urban air environments. Apart from pollutant source control, sustainable street design is another significant technique to reduce street air pollution. Under the validation by wind tunnel data, this paper conducts computational fluid dynamic (CFD) simulations by RNG k-e model to investigate the impacts of typical street layouts and wall heating on the dispersion of gaseous pollutants and particles (diameter d = 1 µm, 5 µm, 20 µm) in the target street canyons and their reentry toward downstream streets. The dispersion processes of gaseous pollutants and fine particles (d = 1 µm) are found similar. For uniform street layouts (aspect ratio H/W = 1) with small Froude number (Fr = 0.19–0.38), leeward-wall heating, ground heating and all-wall heating significantly enhance the primary clock-wise vortex and improve pollutant dispersion, but windward-wall heating does not. Taller upstream buildings (H1/W = 2–3) produce a clockwise vortex over the target canyon and a much weaker counter-clockwise vortex within it, seriously weakening the capacity of pollutant dispersion. For large particles (d = 20 µm), the major fraction deposits onto street ground because the gravity force dominates particle transportation. For particles of d = 5 µm, the dispersion dynamics are more complicated: In the isothermal case less particles of d = 5 µm suspend in the target canyon than d = 1 µm because the gravity force and particle deposition are more important, however, with all-wall heating more particles of d = 5 µm float in the target canyon because the upward thermal buoyancy force reduces particle deposition onto the ground. Finally for both gaseous pollutants and particles, their bulk concentrations in downstream streets decrease exponentially with increasing distance from the target canyon, whose decreasing rates are quantified. Although further investigations are still required to propose a practical framework, this paper is one of the first attempts to quantify the capacity of street particle dispersion for street design purpose.

No oxidative stress or DNA damage in peripheral blood mononuclear cells after exposure to particles from urban street air in overweight elderly.

Exposure to traffic-related particulate matter (PM) has been associated with increased risk of lung disease, cancer and cardiovascular disease especially in elderly and overweight subjects. The proposed mechanisms involve intracellular production of reactive oxygen species (ROS), inflammation and oxidation-induced DNA damage studied mainly in young normal-weight subjects. We performed a controlled cross-over, randomised, single-blinded, repeated-measure study where 60 healthy subjects (25 males and 35 females) with age 55–83 years and body mass index above 25kg/m2 were exposed for 5h to either particle-filtered or sham-filtered air from a busy street with number of concentrations and PM2.5 levels of 1800/cm3 versus 23 000/cm3 and 3 µg/m3 versus 24 µg/m3, respectively. Peripheral blood mononuclear cells (PBMCs) were collected and assayed for production of ROS with and without ex vivo exposure to nanosized carbon black as well as expression of genes related to inflammation (chemokine (C-C motif) ligand 2, interleukin-8 and tumour necrosis factor), oxidative stress response (heme oxygenase (decycling)-1) and DNA repair (oxoguanine DNA glycosylase). DNA strand breaks and oxidised purines were assayed by the alkaline comet assay. No statistically significant differences were found for any biomarker immediately after exposure to PM from urban street air although strand breaks and oxidised purines combined were significantly associated with the particle number concentration during exposure. In conclusion, 5h of controlled exposure to PM from urban traffic did not change the gene expression related to inflammation, oxidative stress or DNA repair, ROS production or oxidatively damaged DNA in PBMCs from elderly overweight human subjects.

Controlled exposure to particulate matter from urban street air is associated with decreased vasodilation and heart rate variability in overweight and older adults.

BackgroundExposure to particulate matter (PM) is generally associated with elevated risk of cardiovascular morbidity and mortality. Elderly and obese subjects may be particularly susceptible, although short-term effects are poorly described.MethodsSixty healthy subjects (25 males, 35 females, age 55 to 83 years, body mass index > 25 kg/m2) were included in a cross-over study with 5 hours of exposure to particle- or sham-filtered air from a busy street using an exposure-chamber. The sham- versus particle-filtered air had average particle number concentrations of ~23.000 versus ~1800/cm3 and PM2.5 levels of 24 versus 3μg/m3, respectively. The PM contained similar fractions of elemental and black carbon (~20-25%) in both exposure scenarios. Reactive hyperemia and nitroglycerin-induced vasodilation in finger arteries and heart rate variability (HRV) measured within 1 h after exposure were primary outcomes. Potential explanatory mechanistic variables included markers of oxidative stress (ascorbate/dehydroascorbate, nitric oxide-production cofactor tetrahydrobiopterin and its oxidation product dihydrobiopterin) and inflammation markers (C-reactive protein and leukocyte differential counts).ResultsNitroglycerin-induced vasodilation was reduced by 12% [95% confidence interval: −22%; −1.0%] following PM exposure, whereas hyperemia-induced vasodilation was reduced by 5% [95% confidence interval: −11.6%; 1.6%]. Moreover, HRV measurements showed that the high and low frequency domains were significantly decreased and increased, respectively. Redox and inflammatory status did not change significantly based on the above measures.ConclusionsThis study indicates that exposure to real-life levels of PM from urban street air impairs the vasomotor function and HRV in overweight middle-aged and elderly adults, although this could not be explained by changes in inflammation, oxidative stress or nitric oxide-cofactors.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-015-0081-9) contains supplementary material, which is available to authorized users.

How much can air conditioning increase air temperatures for a city like Paris, France?

AbstractA consequence of urban heat islands in summer is an increase in the use of air conditioning in urbanized areas, which while cooling the insides of buildings, releases waste heat to the atmosphere. A coupled model consisting of a meso‐scale meteorological model (MESO‐NH) and an urban energy balance model (TEB) has been used to simulate and quantify the potential impacts on street temperature of four air conditioning scenarios at the scale of Paris. The first case consists of simulating the current types of systems in the city and was based on inventories of dry and evaporative cooling towers and free cooling systems with the river Seine. The other three scenarios were chosen to test the impacts of likely trends in air conditioning equipment in the city: one for which all evaporative and free cooling systems were replaced by dry systems, and the other two designed on a future doubling of the overall air conditioning power but with different technologies. The comparison between the scenarios with heat releases in the street and the baseline case without air conditioning showed a systematic increase in the street air temperature, and this increase was greater at nighttime than day time. It is counter‐intuitive because the heat releases are higher during the day. This is due to the shallower atmospheric boundary layer during the night. The increase in temperature was 0.5 °C in the situation with current heat releases, 1 °C with current releases converted to only sensible heat, and 2 °C for the future doubling of air conditioning waste heat released to air. These results demonstrated to what extent the use of air conditioning could enhance street air temperatures at the scale of a city like Paris, and the importance of a spatialized approach for a reasoned planning for future deployment of air conditioning in the city.