Effect of urban morphology and greening on noise and air pollution – case studies including disease burden estimates Jens Forssén 1 Chalmers University of Technology, Architecture and Civil Engineering, Gothenburg, Sweden

Marie Haeger-Eugensson 2 COWI AB, Sweden Gothenburg University, Department of Earth Sciences, Sweden

Meta Berghauser Pont 3 Chalmers University of Technology, Architecture and Civil Engineering, Gothenburg, Sweden

Andreas Gustafson 4 Chalmers University of Technology, Architecture and Civil Engineering, Gothenburg, Sweden

Christine Achberger 5 COWI AB, Sweden

Niklas Rosholm 6 City of Gothenburg, Environmental Office, Sweden

ABSTRACT Exposure of both noise and air pollution due to road traffic in urban environments has been calculated and evaluated for multiple cases. A model study in an urban setting used 31 cases of building morphologies and traffic concentration. An evaluating second set was based on a real case of an arterial road transformed into a boulevard. Besides the effect of building morphology, the effects of driving speed, electric vehicles and urban greening were studied. The levels of noise exposure (L den and L night at housing façades) and air pollution (NO 2 and PM 10 at sidewalks and yards) were calculated as input to estimating the health impact using DALY (Disability-Adjusted Life Years). Concluding from the results, the best solution from a noise perspective is closed blocks with green roofs, while the best solution concerning air quality is point buildings or closed blocks with added high towers. Urban greening was shown to improve the noise situation in general whereas air quality varied due to the interaction between wind speed, dispersion, and filtering effect of leaves. Urban planning guidelines were formulated, including also suggestions of traffic concentration by locating all local traffic to a single widened road as well as transitioning to electric vehicles in combination with reduced vehicle speed.

1 jens.forssen@chalmers.se 2 mrhr@cowi.com 3 meta.berghauserpont@chalmers.se 4 andgusta@chalmers.se 5 char@cowi.com 6 niklas.rosholm@miljo.goteborg.se

Sia inter noice 21-24 AUGUST SCOTTISH EVENT CAMPUS GLASGOW

1. INTRODUCTION

A good living environment regarding both air and noise situations can be difficult to achieve in sustainable urban development projects where densification is often in focus. According to the World Health Organization (WHO), air pollution and environmental noise are the two largest environmental factors in Europe regarding burden of disease [1,2].

In a recently completed research project, we have investigated what improvements can be made possible through early choice of neighbourhood structure and building typology in urban planning. First, a larger model study was conducted, with 31 city morphologies including variation in building structure, building height, block size, traffic concentration and vegetation. Then a case study was carried out based on a real location (the arterial road Dag Hammarskjöldsleden in Gothenburg) where a main traffic route is planned to be transformed into a city boulevard. Five different plan proposals were evaluated where the impact of road traffic, building block structure and building form was simulated regarding both noise and air pollution as well as their health effects.

Within the project, we have calculated how the building typologies and building density affect the noise level at each resident's façade, as well as the levels of nitrogen dioxide and particles in the living environments in connection with the buildings, which connects to the current guideline values for noise and air quality. The research on health effects is also based on façade levels in terms of noise and on outdoor living areas in terms of air quality, and thereby we can use the DALY measure to estimate the corresponding health effects. DALY is a quantified measure of how many disability- adjusted life years are lost depending on exposure levels to various environmental factors, e.g., noise and air quality.

There is a fundamental goal conflict between sound environment and air quality in that a more closed block structure (perimeter lock) on the one hand creates access to quiet façades in courtyards but on the other hand creates closed street spaces that may cause elevated levels of nitrogen dioxide and particles. Within the project, we have investigated which solutions can be advantageous regarding both the sound environment and the air pollution.

In urban planning today, noise and air pollution are often treated as two separate problems, even if some of the situations could be solved with the same measures. The separate handling may lead to reduced efficiency in the construction and planning processes and resulting unnecessary deficiencies in the building designs. 2. METHOD

2.1 Choice of urban morphologies

Model study

The model study was based on 31 different urban morphologies that differ in terms of building typology (from more closed blocks to I-shaped buildings and point buildings), block size, building height, traffic concentration, street width and vegetation. (See Figures 1 and 2.) In the model study, we investigated the effect of one variable at a time to better understand its individual effect on the noise exposure (in terms of L den and L night at housing façades) and on the air pollution (in terms of NO 2 and PM 10 at sidewalks and yards). For example, we calculated the noise exposure and air pollution levels for all building typologies where building height and block size were constant. In another simulation, we calculated for the same building typologies but with varied building heights such that the built intensity (floor space index, FSI) was constant. (For further reading about methodology used for the development of the urban morphology cases, see [3].)

Figure 1: Overview of the urban morphologies used in the model study. A total of about thirty morphologies were examined, including variation in building structure, number of storeys, traffic concentration and vegetation.

Figure 2: The model study used an existing urban area for placement of the fall examples, here exemplified for 15 closed blocks.

Real-case based study

In the real-case based study, we started from a transformation of the arterial road Dag Hammar- skjöldsleden into a city boulevard as a place to study the effect of five different plan proposals on the noise exposure and air pollution levels. At present, the city of Gothenburg is at an early stage of this transformation to Dag Hammarskjöld's boulevard and the project's plan proposals are designed freely in relation to the city's plans, but with the intention of exemplifying realistic environments based on the results of the model study. We call them scenarios 1-5, with additions for the impact of vegetation and traffic changes for scenario 1.

Scenario 1 is what we call the zero scenario with only closed blocks of 5 floors. Scenario 2 tests the same building structure but with taller buildings in the northern part of the boulevard. In scenario 3, the closed quarters are opened slightly in strategic places that were shown to be favourable in the model study regarding air quality without giving a too negative impact on the sound environment. Scenario 4 uses another solution that was shown to be positive for both sound environment and air quality in the model study, in terms of adding taller buildings (towers) to the more traditional closed blocks of 5 storeys. Such a variation in building height generally does not impair the noise exposure but may improve the air flows that benefit air quality. For the case study, these accents with higher buildings were chosen strategically and do not only benefit the sound environment and air quality but also create a higher density along the boulevard and more variety in the building forms. Scenario 5 is a combination of scenarios 3 and 4 where openings in the block and a varying building height have been applied. (Scenario 5 is shown in Figure 3.)

Figure 3: One of the cases of study, with varying building heights and openings in the façade (scenario 5). 2.2 Calculation methods

Estimation of health effects

For environmental factors that describe environmental noise and air quality, dose-response relationships are used to estimate the health impact of each exposure level. On the one hand, the noise level at the respective residents' façade, and on the other hand, the levels of nitrogen dioxide and particles in the living environments in connection with the buildings are used as input data. The total health effect for sound and air environment is then evaluated via estimates of the DALY quantity per person. (For further details, see [3].) Based on the DALY results for both air quality and noise exposure, different building alternatives can be evaluated.

Noise exposure calculations

Noise levels ( L Aeq24h ) were calculated for façade elements and for living areas consisting of courtyards and sidewalks in the area. The calculations were made with a combination of a commercial noise calculation software (SoundPLAN, version 8.0) and a separate additional method for indirect noise contribution to courtyards (based on results from the Qside project [4]). The calculations with the noise calculation software were made according to the Nord2000 Road model with five reflections and neutral weather. The frequency range consisted of the one-third octave bands from 25 Hz to 10 kHz. The combined model uses the results, in the form of A-weighted singular values, from both the Nord2000 model and the additional method for indirect noise contribution. The Nord2000 model results, which generally greatly underestimates noise levels in enclosed courtyards, are replaced by the indirect noise contribution at all points where it results in a higher level than the Nord2000 model. The calculated façade levels are then converted to L den and L night levels and used together with the population number for each typology to calculate the exposure and thereafter the DALY value. (For a more detailed description of the methodology, see [3].)

Air pollution calculations

For the air pollution calculations, 3D computational fluid dynamics (CFD) modelling was carried out for the street canyons and in the yards of the buildings, including the impact of the surrounding buildings to obtain realistic wind field and thus dispersion conditions. The calculated levels obtained in the areas in the vicinity of the housing, i.e., the street canyon and the yards of the buildings, are then used as input data for exposure calculations together with the population data. The number of DALY was calculated for each area studied within the model study whereas for the real-case based study air pollution results were used alone. 3. RESULTS

The calculated and evaluated results from the model study and from the real-case based study are here summarized in the form of planning guidelines. The guidelines are aimed for use in the early stages of urban planning, where the building design can still be influenced, and depending on the actual planning project, situational adjustments should be considered for example regarding the orientation of openings and the choice of height and location of towers. Furthermore, the results concerning urban greening showed a general improvement to the noise situation, using green roofs or façade vegetation, whereas the impact on air quality varied depending on the interaction between wind speed, dispersion, and filtering effect of leaves.

The following summarizing points can be a guide in the early stages of urban planning for improving the sound environment and the air quality.

! When planning for a good environment concerning both noise exposure and air pollution, it is important to be aware of goal conflicts. The building structure needs to be well thought trough, as well as the choice and location of vegetation and surfaces of acoustics absorption. ! The best solution from a noise perspective is closed blocks with green roofs, while the best solution from an air quality perspective is point buildings or closed blocks with added high towers. ! A good solution from both a noise and air perspective is closed blocks with smaller openings and green (sound-absorbing) façades at these openings. When planning openings in the corner of the block, the noise contribution to the courtyard can be limited with the help of absorbing façades and by keeping the size of the openings down. ! Boulevardisation in the form of a widened street provides a positive health effect concerning both air quality and sound environment if the traffic in the area is simultaneously concentrated to the boulevard. For the most noise-exposed façades, additional measures may be planned; geometric variations of the façades can also provide improvement.

! Switching to electric vehicles and reduced speed improves both the sound environment and the air quality. ! Densification of closed blocks through increased building height with allowed increase in traffic is generally to the detriment of both the air quality and the sound environment. But if the increase in traffic can be avoided, increased building height gives an improved noise situation. ! Densification regarding both air quality and sound environment is best made by supplementing closed blocks with towers. ! Increasing the size of closed blocks is generally to the detriment of both the air quality and the sound environment. 4. CONCLUSIONS

A parametric model study and a real-case based study have been carried out to investigate the effects of urban morphology on the exposure of both noise and air pollution due to road traffic. Besides the effect of building morphology, the effects of driving speed, electric vehicles and urban greening were studied. The levels of noise exposure ( L den and L night at housing façades) and air pollution (NO 2 and PM 10 at sidewalks and yards) were calculated and used as input to estimate the health impact using DALY (Disability-Adjusted Life Years) per person. Using the calculated results, guidelines for early stages of urban planning have been suggested. ACKNOWLEDGEMENTS

The research project was funded mainly by Formas (Dnr 2017-00914) [5] and partly by COWIfonden . REFERENCES

1. Burden of disease from environmental noise. Quantification of healthy life years lost in Europe.

WHO (2011). 2. WHO press release: Burden of disease from environmental noise 3. Forssén, J. et al. , Effects of urban morphology on traffic noise: A parameter study including

indirect noise exposure and estimated health impact , Applied Acoustics . Elsevier, 186, p. 108436 (2022). doi: 10.1016/J.APACOUST.2021.108436 4. Wei, W. et al. , Urban background noise mapping: The general model , Acta Acustica united

with Acustica . S. Hirzel Verlag GmbH, 100(6), pp. 1098–1111 (2014). doi: 10.3813/AAA.918789 5. https://www.chalmers.se/en/projects/Pages/Increasing-citiesQ-capacity-to-manage-noise-and-

air-quality.aspx