Photo: Cristiana Raluca

Last week saw some incredible action in the fight against climate change—from the UN Climate Action Summit and continuing on to the Global Climate Strike. All the while, the battle for clean air continues with many cities around the world rethinking transportation in and around neighbourhoods. Reducing or eliminating traffic and combustion engines in the urban landscape has been a strong lever for cities as residents raise their voices against climbing pollution levels.

Photo by Adrianna Calvo
Barcelona’s Superblocks promise to transform neighborhoods into walkable, mixed-used public spaces.

But what actually happens when you dramatically reduce traffic in a major urban center? We aimed to find out during Paris’ Journée Sans Voitures (JSV)—from the bird’s eye to the bike lanes. 

What we did:

Step 1: The team took pollution levels from our environmental data platform in and around Paris during JSV 2019 and compared them to the historical data for past Sundays. 

Step 2: Then we took a look at what was going on at the street and neighborhood level by using our street by street pollution mapping system—the same one you can find in the Flow app.

Step 3: Finally, we took to the streets on our bikes to get some real-time personal exposure data using our Flows.

Paris average pollution levels between 2am and 6pm September 22, 2019

What we discovered

The nutshell

  1. There was a lot of ambient pollution in the region during JSV.
  2. We can see positive results of JSV based on the difference between readings inside when compared to those close to the city limits (outside the car-free zone) despite the regional conditions.
  3. Cyclists were still exposed to some pollution peaks while biking through the city—even with the reduced traffic. 

The details

The first conclusion we can draw from our analysis is: Even though regional levels of pollution were elevated, the average pollution levels measured within the car-free zone that day were low compared to historical standards. 

The average Plume Index measured from 11AM to 6PM by stations located in Paris

Pollution levels were higher outside Paris than inside that day

In fact, September 22nd (the green bar at the end of the graph above) had the lowest Plume AQI rating from 11AM to 6PM since September 1st. We can see the pronounced decrease in pollution when compared to the 4 past days (which were among the most polluted this month). We also found that there was a significant decrease in air pollution when compared to other Sundays in the month.

Solid lines – September 22nd
Dashed lines – Average of the three past Sundays (September 15th, 8th and 1st)

The effect JSV 2019 had on air quality is most obvious when we compare the data taken from air quality monitoring stations within Paris’ circumferential highway (the green line in the graph above) with data taken from stations located outside this boundary (the red line).

At this point, you may ask yourself “what happened at 2:00 PM?” the answer is: rain! Rain is a very efficient way to remove pollution from the atmosphere as particles and gas molecules are trapped by raindrops. 

Paris average pollution levels between 2am and 6pm September 22, 2019

This is also evident in the street by street map of the average pollution levels for Paris and surrounding areas for the same time period (above).

Finally, what did our wheels on the ground find?

Our cyclists found that, despite the overall improvements to the air quality in the city, they were still finding high points of pollution during their rides. These dramatic drops in air quality were noted when they were at intersections with traffic (not all streets were cleared of cars).

Screen captured from one of our cyclist’s Flow app after a ride through Paris during the Journée Sans Voitures 2019


Based on the data, this year’s Journée Sans Voitures was a success in terms of limiting air pollution within the city. Beyond that, there are lots of reasons to run these types of events: raising awareness, promoting active transportation, and bringing people together to see their city with new eyes.

Here’s to clean air and keeping the rubber side down.

—the Team at Plume Labs

Do you have a story we can help you tell? Drop us a line at

Leave a Reply

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

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

Facebook photo

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

Connecting to %s

About Plume Labs

We're here to help you understand what you breathe and take meaningful action against air pollution.


Non classé