In the recent years, the center of Eindhoven served as a ‘Living Lab’ for research into smart integration of air purification technology in the public environment, within the scope of the Lungs of the City project. The key question being: ‘What is the added value of targeted integration of air purification for the improvement of urban air quality?’ The study investigated to what extent particulate matter concentration can be reduced, during relevant periods, and how this translates into a reduction of health risk, an indicator which is of great importance for embedment of mitigation measures in (local) policies. This project was carried out by a consortium consisting of the municipality of Eindhoven, Eindhoven University of Technology, Air Liquide, and ENS Clean Air.

Improvement of air quality at hotspot locations

Lungs of the City is an approach to improve the air quality and quality of life in cities, with the aim of reducing particulate matter concentrations at locations where high concentrations coincide with a high degree of public exposure; the so-called hotspots. The idea arose after the first application of ENS air purification technology in a public parking garage in 2014. Reductions in particle matter concentrations were not only measured inside the parking garage, but were also observed by local shopkeepers and people living nearby, in the form of reduced by pollution levels. This was followed by a scientific study in 2016, in which the potential of implementation of air purification in parking garages was assessed for the city center of Eindhoven. Using airflow simulations, it was shown that the Lungs of the City approach has great potential. Particulate matter concentrations were reduced by 30 to 50% in the direct vicinity of parking garages and by 10% up to a distance of one kilometer.

To assess the of the Lungs of the City in practice, an experimental study was carried out on the city hall square (Stadhuisplein) in Eindhoven from 2017 to 2018: an air purification setup removed particulate matter from the (ventilation) exhaust air, of the parking garage below the square, and then released the purified air over the square. Measurements were carried out on, and in the direct vicinity of the square, using high-end monitoring equipment for particulate matter concentrations and weather conditions. Measurements showed that:

  • Depending on the location, there are large differences in local particulate matter concentrations as a result of variation in environmental characteristics such as building density, presence of traffic and local flow phenomena.
  • Particulate matter in the city center mainly consists (71%) of the smaller, most harmful particulate fraction (PM1).
  • The daily average PM2.5 WHO guideline values were frequently exceeded. 
  • The particulate matter concentrations in the underground parking garage are substantially higher than the background concentrations in the city. The particulate matter concentration in the parking garage’s ventilation exhaust air can be substantially reduced by air purification (to below the background concentration); the parking garage is thus transformed into an air-purifying element.

Implementation of the (measurement) results from the effect studies in Eindhoven and other projects led to refinement and a recalibration of the calculation method. High-resolution computers models of the Eindhoven city center showed that: 

  • The required air purification capacity, as applied in the feasibility study, appeared to be over-estimated: The ambient air quality improvement, by means of air purification in parking garages, is achievable with only 55% of the originally calculated purification capacity.
  • The effect of the applied air purification differs per location. The study showed the impact of situational and environmental characteristics such as buildings, traffic and weather influences, on the distribution of clean air. By taking into account such factors in computer models, an accurate pre-assessment of each mitigation measure can be performed. With more applications, cumulative effects can be achieved, which cover a larger area.
  • The Lungs of the City approach can be adopted in the (urban) development of healthy cities by means of practice-oriented business models. 

Effective approach through smart integration at hotspot locations

The project results show that Lungs of the City is a technically feasible strategy that can contribute to significant reductions in particulate matter exposure. The Lungs of the City concept can be integrated into the urban environment in many ways. Parallel to the Lungs of the City project in Eindhoven, several related research projects and impact studies (based on integration of active air purification in existing infrastructure) have been carried out worldwide. At area scale, air purification has been applied in traffic-intensive areas, such as next to a highway, in a traffic tunnel, in narrow city streets (street canyons), in a city park, in schoolyards and in vehicles such as street sweepers. At building scale, it concerns applications in various parking garages, train and metro stations, a bus terminal and the courtyard of a school building.

With the emerging insight into targeted implementation of the Lungs of the City approach, an important instrument has been added to the toolkit for sustainable city development and improvement of the living environment. The city of the future can be self-purifying, and the first steps to make this achievable have been taken in Eindhoven.

Would you like to learn more about Lungs of the City or are you curious to find out how this approach can be integrated? Feel free to contact us.