Pontus Thorsson

Influence of urban vegetation on air pollution and noise exposure – A case study in Gothenburg, Sweden

Air pollution levels (NO2, PAHs, O3) were investigated, before (BLE) and after (ALE) leaf emergence, in the urban landscape of Gothenburg, Sweden. The aims were to study the 1) spatial and temporal variation in pollution levels between urban green areas, 2) effect of urban vegetation on air pollution levels at the same distance from a major emission source (traffic route), 3) improvement of urban air quality in urban parks compared to adjacent sites near traffic, 4) correlation between air pollution and noise in a park. O3 varied little over the urban landscape. NO2 varied strongly and was higher in situations strongly influenced by traffic. Four PAH variables were included: total PAH, total particle-bound PAH, the quantitatively important gaseous phenanthrene and the highly toxic particle-bound benzo(a)pyrene. The variation of PAHs was similar to NO2, but for certain PAHs the difference between highly and less polluted sites was larger than for NO2. At a vegetated site, NO2 and particulate PAH levels were lower than at a non-vegetated site at a certain distance from a busy traffic route. This effect was significantly larger ALE compared to BLE for NO2, indicating green leaf area to be highly significant factor for air quality improvement. For particulate PAHs, the effect was similar BLE and ALE, indicating that tree bark and branches also could be an important factor in reducing air pollution. Parks represented considerably cleaner local environments (park effect), which is likely to be a consequence of both a dilution (distance effect) and deposition. Noise and air pollution (NO2 and PAH) levels were strongly correlated. Comparison of noise levels BLE and ALE also showed that the presence of leaves significantly reduced noise levels. Our results are evidence that urban green spaces are beneficial for urban environmental quality, which is important to consider in urban planning.

Combined effects of admittance optimisation on both barrier and ground

Abstract The focus of this paper is on the problem of finite impedances on both ground and barrier. Using a boundary element approach the surface treatment of the barrier and finite parts of the ground have been optimised to yield maximum insertion loss at multiple frequencies simultaneously. A 1 m high T-shaped barrier optimised in this way gives up to 8 dB higher insertion loss than a rigid barrier of equal shape. Optimisation of the acoustical properties of the ground below the source as well as those of the barrier improves the insertion loss dramatically for all receiver heights. The ground close to the source is the part of the ground that influences the insertion loss most, and in such a way that the radiation properties of the source are altered, and the radiated sound power is reduced. Having an optimised admittance only on the ground close to the barrier gives only a minor effect. A barrier–ground combination with specialised treatment on the ground close to the source and on the barrier top gives an increase in insertion loss that is comparable to the optimised results. The main conclusion of this paper is that specialised surface treatments provide largest effect if they are used on the ground surface.

Low-frequency outdoor-indoor noise level difference for wind turbine assessment

To increase the understanding of wind turbine noise on sleep, human physiological reactions need to be studied in a controlled laboratory setting. The paper presents an outdoor-indoor noise level difference as a function of frequency, applicable to creating wind turbine indoor sounds with the outdoor sounds as input. For this, a combination of measurement data and modeling results has been used. The suggested data are provided in a table.