Article available under the terms of the CC-BY-NC-ND licence (https://creativecommons.org/licenses/by-nc-nd/4.0/) eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. Abstract: Soundscape research represents a paradigm shift from noise control policies towards a new multidisciplinary approach as it involves not only physical measurements but also the cooperation of humanity and social sciences to account for the diversity of soundscapes across countries and cultures, with more focus on how people actually experience the acoustic environments; and it considers environmental sounds as a 'resource' rather than a 'waste'. The ten questions presented in this paper range from the very basic definitions underlying the emerging soundscape 'science', to more applied topics about how to use soundscape as a design approach for the planning and management of the built environments. Although significant research activity has been conducted so far, there is still a need to systematically provide the underpinning science and practical guidance in soundscaping. Thus, the last question aims to identify the most crucial gaps in soundscape research and set the agenda for future advancements in the field.

This paper illustrates the use of a numerical time-domain simulation based on the finite-difference time-domain (FDTD) approximation for studying low- and middle-frequency room acoustic problems. As a direct time-domain simulation, suitable for large modeling regions, the technique seems a good ‘‘brute force’’ approach for solving room acoustic problems. Some attention is paid in this paper to a few of the key problems involved in applying FDTD: frequency-dependent boundary conditions, non-Cartesian grids, and numerical error. Possible applications are illustrated with an example. An interesting approach lies in using the FDTD simulation to adapt a digital filter to represent the acoustical transfer function from source to observer, as accurately as possible. The approximate digital filter can be used for auralization experiments.

Mobile monitoring is increasingly used as an additional tool to acquire air quality data at a high spatial resolution. However, given the high temporal variability of urban air quality, a limited number of mobile measurements may only represent a snapshot and not be representative. In this study, the impact of this temporal variability on the representativeness is investigated and a methodology to map urban air quality using mobile monitoring is developed and evaluated.A large set of black carbon (BC) measurements was collected in Antwerp, Belgium, using a bicycle equipped with a portable BC monitor (micro-aethalometer). The campaign consisted of 256 and 96 runs along two fixed routes (2 and 5 km long). Large gradients over short distances and differences up to a factor of 10 in mean BC concentrations aggregated at a resolution of 20 m are observed. Mapping at such a high resolution is possible, but a lot of repeated measurements are required. After computing a trimmed mean and applying background normalisation, depending on the location 24 to 94 repeated measurement runs (median of 41) are required to map the BC concentrations at a 50 m resolution with an uncertainty of 25 %. When relaxing the uncertainty to 50 %, these numbers reduce to 5 to 11 (median of 8) runs. We conclude that mobile monitoring is a suitable approach for mapping the urban air quality at a high spatial resolution, and can provide insight into the spatial variability that would not be possible with stationary monitors. A careful set-up is needed with a sufficient number of repetitions in relation to the desired reliability and spatial resolution. Specific data processing methods such as background normalisation and event detection have to be applied.

Recent studies show that introducing sound from water features in urban open spaces may reduce the loudness of road traffic noise, but it is not clear in which situations this measure also improves overall soundscape quality. This work describes a listening experiment on loudness, pleasantness, and eventfulness of stimuli that combine road traffic noise with fountain or bird sound at different sound levels. Adding fountain sound reduced the loudness of road traffic noise only if the latter had low temporal variability. Conversely, adding bird sound significantly enhanced soundscape pleasantness and eventfulness, more than what was achieved by adding fountain sound.

Reduction of noise is one of the multiple benefits of building envelope greening measures. The potential of wall vegetation systems, green roofs, vegetated low screens at roof edges, and also combinations of such treatments, have been studied by means of combining 2D and 3D full-wave numerical methodologies. This study is concerned with road traffic noise propagation towards the traffic-free sides of inner-city buildings (courtyards). Preserving quietness at such locations has been shown before to be beneficial for the health and well-being of citizens. The results in this study show that green roofs have the highest potential to enhance quietness in courtyards. Favourable combinations of roof shape and green roofs have been identified. Vegetated façades are most efficient when applied to narrow city canyons with otherwise acoustically hard façade materials. Greening of the upper storey's in the street and (full) façades in the courtyard itself is most efficient to achieve noise reduction. Low-height roof screens were shown to be effective when multiple screens are placed, but only on conditions that their faces are absorbing. The combination of different greening measures results in a lower combined effect than when the separate effects would have been linearly added. The combination of green roofs or wall vegetation with roof screens seems most interesting.Keywords urban sound propagation, green roofs, green walls, noise reduction, numerical simulations, road traffic noise 3 1.IntroductionThe use of vegetation has become an essential aspect in urban planning nowadays. In densely built-up city centers, building envelope greening is often the only possibility to meet this demand. These measures have many ecological advantages too, ranging from increasing the thermal insulation of the building envelope and reduction of urban heat island effects [1]- [9], acting as a buffer for storm water [9]- [14], improving air quality and increased carbon dioxide uptake [15]- [17], increasing urban biodiversity [18]- [22], providing a visually pleasant environment [23], to even crop harvesting. In addition, also from an economical point of view, building greening seem interesting [24]- [27]. Recently, the noise reducing possibilities of such building envelope greening measures have been identified [28][29] [30][31] [32].The presence of mainly acoustically rigid materials in cities (streets, bricks, concrete, glazings, etc.) leads to a strong amplification of the emitted sound from road traffic noise, and large sound pressure levels are observed in city canyons. The noise problem has indeed become one of the major environmental challenges in the urban environment. The WHO report "burden of disease by environmental noise" [33] quantified the many health-related effects by long-term exposure to environmental noise. The positive influence of quiet urban areas, as a possible mitigating measure, has been shown before [34][35] [36] and has become part of European noise policy [37]. As a result, the sound environment in poten...

The finite-difference time-domain (FDTD) approximation can be used to solve acoustical field problems numerically. Mainly because it is a time-domain method, it has some specific advantages. The basic formulation of the FDTD method uses an analytical grid for the discretization of an unknown field. This is a major disadvantage. In this paper, FDTD equations that allow us to use a nonuniform grid are derived. With this grid, tilted and curved boundaries can be described more easily. This gives a better accuracy to CPU–resource ratio in a number of circumstances. The paper focuses on the new formulation and its accuracy. The problem of automatically generating the mesh in a general situation is not addressed. Simulations using quasi-Cartesian grids are compared to Cartesian grid results.

Road traffic noise propagation through a vegetation belt of limited depth (15 m) containing periodicallyarranged trees along a road is numerically assessed by means of 3D finite-difference time-domain (FDTD) calculations. The computational cost is reduced by only modeling a representative strip of the planting scheme and assuming periodic extension by applying mirror planes. With increasing tree stem diameter and decreasing spacing, traffic noise insertion loss is predicted to be more pronounced for each planting scheme considered (simple cubic, rectangular, triangular and face-centered cubic). For rectangular schemes, the spacing parallel to the road axis is predicted to be the determining parameter for the acoustic performance. Significant noise reduction is predicted to occur for a tree spacing of less than 3 m and a tree stem diameter of more than 0.11 m. This positive effect comes on top of the increase in ground effect (near 3 dBA for a light vehicle at 70 km/h) when compared to sound propagation over grassland. The noise reducing effect of the forest floor and the optimized tree belt arrangement are found to be of similar importance in the calculations performed. The effect of shrubs with typical above-ground biomass is estimated to be at maximum 2 dBA in the uniform scattering approach applied for a light vehicle at 70 km/h. Downward scattering from tree crowns is predicted to be smaller than 1 dBA for a light vehicle at 70 km/h, for various distributions of scattering elements representing the tree crown. The effect of the presence of tree stems, shrubs and tree crowns is predicted to be approximately additive.Inducing some (pseudo)randomness in stem centre location, tree diameter, and omitting a limited number of rows with trees seem to hardly affect the insertion loss. These predictions suggest that practically achievable vegetation belts can compete to the noise reducing performance of a classical thin noise barrier (on grassland) with a height of 1 to 1.5 m (in a non-refracting atmosphere).

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