Les Halles: Open space/public space

“I need green to feel good.”

“A public space without vegetation is not a good public space.”

– Parisians at Les Halles

Anne Hidalgo has decided to prioritize the creation of more green spaces in Paris, which would contribute towards several sustainable development goals of the United Nations, namely climate control, biodiversity preservation, and improved health1 and well-being of citizens.

Our study focuses on the effect of vegetation levels and air pollution on the quality of a public space in the center of Paris. We studied three public places at Les Halles: the canopy, Place Joachim-du-Bellay, and the park.


team_5_2Place Joachim-du-Bellay



Our methodology includes three components:

  1. A calculation of the proportion of each area covered by vegetation using GéoPortail (area covered by vegetation/total area).
  1. Measurements of air quality (concentration in µg of PM1.0 particles per m3) at several locations in each place using a Shinyei particle sensor.
  1. A survey in each place on people’s perception of the quality of the public place, air quality, and vegetation level. We asked the following questions to 20 people in each place:
    1. On a scale of 1 to 10, how do you feel in this public space ?
    2. On a scale of 1 to 10, what do you think of the air quality ?
    3. What do you think of the level of vegetation ?

Data & Analysis

  1. Proportion of each area covered in vegetation = area covered by vegetation/total area


0 m2/8141 m2 = 0% vegetation cover

Place Joachim-du-Bellay

1314.81 m2/6101.89 m2 = 22% vegetation cover


10864.54 m2/18460.83 m2 = 59% vegetation cover

We can rank the places from lowest vegetation level to highest vegetation level :

canopy (0%), Place Joachim-du-Bellay (22%), and the park (59%).

  1. Map with air quality measurements

The data suggests that proximity to construction and possibly traffic are the major determinants of microparticle concentration in the air on such a local scale. Areas closer to construction sites had higher microparticle concentrations (94 µg/m3 in the park and 70 µg/ m3 in Place Joachim-du-Bellay) while areas farther away had lower concentrations (20-22 µg/ m3 in the park and 30-35 µg/ m3 in Place Joachim-du-Bellay). There is no clear correlation between vegetation level and air quality. For example, the canopy showed a relatively low concentration of microparticles (25 µg/m3 on the upper level), even though it has no vegetation (this may be due to air flow).

  1. Survey results


Figure 1 – The graph shows the average well-being and perceived air quality values obtained from the 20 people surveyed in each area.


Figure 2 – This graph shows the expected level of vegetation of the 20 respondents in each place.

These results show that demand for more vegetation rises in places with lower vegetation levels, with 15/20 respondents desiring more vegetation under the canopy, compared to 13/20 in Place Joachim-du-Bellay, and 9/20 in the park. In all three places, no respondent thought there was too much vegetation. Given the park’s relatively high vegetation level (59%), we were surprised that about half of those surveyed were unsatisfied with the current vegetation level.

The results do not show a correlation between vegetation level and overall satisfaction with the public place, likely because there are many uncontrolled variables differentiating the three places.

The results do not indicate a correlation between vegetation level and perceived air quality. Respondents found the canopy’s air quality to be higher than that of Place Joachim-du-Bellay and roughly equal to that of the park. This could be due to the lack of car traffic near the canopy. Respondents seemed surprised by this question and unsure of how to judge air quality.


Figure 3 – An example of lights strung in trees at « Festival arbre et lumière », Genève. Photo credit : D. Wohlschlag / Ville de Genève


Our analysis leads to the following proposals for each public space:

The park

We propose implementing mature, native fruit trees, adapted to local conditions and favorable to biodiversity. A fruit-picking event would animate the park, promote interaction between users, and enhance the appropriation of space. To highlight both the vegetation and historical monuments, we propose replacing streetlights with lights set in trees and on the facade of St. Eustache Church and the CCI de Paris.

Place Joachim-du-Bellay

Figure 4 – An example of plants around the foot of the tree at Cour Saint André, Nantes. Photo credit : Jardins.nantes.fr

The fountain is the centerpiece of the square, but it is currently not working. The sight and sound of the water would greatly enhance the quality of this public space. We thus propose fixing and maintaining the fountain. To increase vegetation, we propose adding bushes and flowers under the trees.

Figure 5 – An example of a potted tree that could also serve as public seating. Photo credit : http://www.archiexpo.fr


The canopy

The level of pollution is higher downstairs and we should make this space more organic and welcoming. We propose implementing a green wall to clean the air and creating a circular pond with colorful water plants in the middle of the area. The edges of ponds could serve as public seating. Upstairs, directly under the canopy, we propose adding potted trees to create a continuity between the park and the canopy.

Footnotes :

1 According to studies , urban trees remove 711,000 metric tons of pollution, including PM10, O3, NO2, SO2, and CO, each year in the U.S (Nowak et al., 2006). The health costs of air pollution are estimated to be from € 68 to 97 billions per year in France (Sénat, 2015)

References :

 Sénat, 2015 « pollution de l’air : le coût de l’inaction »


Nowak, J. David, Crane, Daniel E., Stevens, Jack C. ; 2006. « Air pollution removal by urban trees and shrubs in the United States » http://www.fs.fed.us/ne/newtown_square/publications/other_publishers/OCR/ne_2006_nowak001.pdf

Tessa Han, Oliver Hansen, Estelle Murail, François Sacquin


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s