1,720,975 research outputs found
Impact of filtering methods on ultrafine particles turbulent fluxes by eddy covariance
No full textIn the present work, a comparison between Linear Detrending (LDT) and a Recursive Digital Filter (RDF) in removing the low-frequency contribution to the vertical turbulent fluxes was performed. The two methods were applied in order to obtain a correct evaluation of ultrafine particles, sensible heat and momentum turbulent fluxes. Exchange velocity was also evaluated separating the positive cases (the so called deposition velocity Vd) from negative cases (named emission velocity Ve). The low-frequency time scales (τc) required by the RDF were obtained by means of an ogive analysis of turbulent fluxes for different atmospheric stability conditions (i.e. unstable, stable and neutral). RDF was applied also with a constant low-frequency time scale (RDF300, τc = 300s). The stationarity test proposed by Mahrt (1998 - MST98) has been applied to momentum, kinematic temperature and particle number fluxes before and after applying LDT and RDF methods, in order to investigate the impact of filtering criteria on stationarity of time series. Results emphasised that there were no significant differences in stationary cases for different filtering procedures. The comparison analysis on the main turbulent variables highlighted that wider discrepancies occurred between LDT and RDF300, showing on average an increase in turbulent number particles flux obtained through RDF methods, especially in unstable atmospheric conditions. On the other hand, a mean decrease for momentum and sensible heat fluxes was observed. Filtering procedures led to a slight increase of exchange velocity, although an underestimation occurred for emission and deposition velocities when considered separately
The effects of trees on micrometeorology in a real street canyon: Consequences for local air quality
No full textThis study analyses the effects of trees on local meteorology of a Mediterranean City (Lecce, IT) using field measurements and computational fluid dynamics simulations. Measurements were collected for 51 days in a street canyon with trees to cover different meteorological and foliage conditions. Building façades and ground temperatures were estimated from infrared images, flow and turbulence measured by ultrasonic anemometers. In the case of approaching wind parallel to the street axis, trees induce large wind direction fluctuations below tree crowns and velocities up to about 80% lower than those at roof top. This, combined with the obstruction by tree crown, lead to lower ventilation in the bottom part of the street, especially during nocturnal hours, and to in-canyon volume-averaged pollutant concentration about 20% larger than in the tree-free case. Ignoring trapping effects of trees, as typically done in many air quality models, may lead to underestimation of ground level concentrations
Challenges in the application of a WRF/Urban-TRNSYS model chain for estimating the cooling demand of buildings: A case study in Bolzano (Italy)
No full textIn the present study, a WRF/Urban-TRNSYS model chain is proposed to evaluate the cooling demand of buildings located in an urban area. A case study is proposed to show the applicability of the method for a hypothetical residential building located in the city of Bolzano (Italy) on a clear-sky hot day in summer. WRF/Urban results were first validated against measurements from permanent weather stations located both in the urban area and in the surrounding countryside. Then, several TRNSYS simulations were performed, in order to assess the impact of the gridded input from WRF/Urban against both measurements from a weather station located close to the sample building and to standard data from the Test Reference Year (TRY). Compared with estimates using input data from the weather station, the daily cooling demand of the sample building estimated by WRF/Urban-TRNSYS differed by only 6% to 8%, while differences of 60% were found when using standard TRY data. Moreover, results show that energy estimates obtained by means of WRF/Urban-TRNSYS model chain satisfy the standard requirement suggested by Ashrae Guidelines 14–2002, suggesting that this model chain is a useful tool for the estimation of real buildings energy consumption
Sensitivity analysis of SEBE model using different meteorological input: A case study in bolzano, Italy
No full textAssessing solar radiation in the urban area of Bolzano, Italy, by Means of SEBE simulations
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Sensitivity analysis of urban microclimatic conditions and building energy consumption on urban parameters by means of idealized numerical simulations
No full textIn the present work the mesoscale meteorological model Weather Research and Forecasting (WRF), coupled with a multilayer urban canopy parameterization and a building energy model (BEP + BEM), is used to analyze the sensitivity of both urban climatic conditions and building energy consumption on parameters characterizing urban materials and the building environment. In particular, simulations in an idealized urban area, with different urban geometry and under different climatic conditions, are compared to evaluate the relative importance of various parameters. Results highlight that the target indoor temperature has the strongest impact on both building energy consumption and external air temperature. Building energy consumption is also significantly affected by other internal building parameters, such as the ventilation rate and the heat produced by equipment and occupants. On the contrary, no significant influence, either on building energy consumption or on air temperature, is found from changes in wall albedo and emissivity
Sensitivity of WRF/urban simulations to urban morphology parameters: A case study in the city of bolzano
No full textThe recent progress in numerical weather prediction modelling, and in particular the possibility to reach increasingly finer spatial resolutions, allowed researchers to reproduce building-atmosphere interactions in a more accurate and realistic way, especially in urban areas. The present work aims at evaluating the impact of highresolution gridded datasets of urban morphology parameters on the results of numerical simulations of atmospheric processes performed with the WRF/Urban suite in the city of Bolzano (Italy), and to analyze how they affect near-ground temperature fields. A sensitivity test was carried out, combining the WRF model with the Building Effect Parameterization (BEP) scheme to simulate two typical clear-sky summer days, respectively with and without the input gridded data of urban morphology. The structure and the morphology of the city of Bolzano were carefully reproduced through several fine-scale morphometric parameters from surface and terrain models (0.5 m resolution). The results highlight that urban morphological parameters display a high spatial variability, moderately affecting the distribution of the temperature field near the ground. High-resolution meteorological fields inside urban areas can be valuable information for building energy simulations. Accordingly, a scheme of model chain coupling WRF and TRNSYS codes is proposed, in order to enhance the future assessment of urbanization effects and in the same way to provide more realistic and accurate building energy simulations
Impact on Ultrafine Particles Concentration and Turbulent Fluxes of SARS-CoV-2 Lockdown in a Suburban Area in Italy
No full textIn order to slow the spread of SARS-CoV-2, governments have implemented several restrictive measures (lockdown, stay-in-place, and quarantine policies). These provisions have drastically changed the routines of residents, altering environmental conditions in the affected areas. In this context, our work analyzes the effects of the reduced emissions during the COVID-19 period on the ultrafine particles number concentration and their turbulent fluxes in a suburban area. COVID-19 restrictions did not significantly reduce anthropogenic related PM10 and PM2.5 levels, with an equal decrement of about 14%. The ultrafine particle number concentration during the lockdown period decreased by 64% in our measurement area, essentially due to the lower traffic activity. The effect of the restriction measures and the reduction of vehicles traffic was predominant in reducing concentration rather than meteorological forcing. During the lockdown in 2020, a decrease of 61% in ultrafine particle positive fluxes can be observed. At the same time, negative fluxes decreased by 59% and our observation site behaved, essentially, as a sink of ultrafine particles. Due to this behavior, we can conclude that the principal particle sources during the lockdown were far away from the measurement site
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