A festive ambiance..... but with vigilant citizens
on the occasion of
Paris 2024 ...
Paris and surrounding area
A place at a special time...
Paris and the surrounding area have the highest density of air quality measurement sensors in France. It therefore seems only natural to pay particular attention to this subject for this place.
The air quality analysis here is conducted over the month of July 2024, a period that included two major events: the festivities of France’s national day (July 14), for which Paris is the highlight, and the start of the 2024 Olympic Games, for which Paris is the organizing city.
In the light of these two events, we can see the impact on air quality of implementing such popular performances.
The network of sensors in and around Paris
A particularly closely monitored environment
In and around Paris, we have 22 official sensors from the AirPrif network (blue triangles on the map opposite) and 50 citizen sensors from the “Sensor Community” network (red dots); not all of these are usable, either because they are inoperative or faulty, or because the data is unavailable (particularly for AirParif sensors), but 80% of them are viable.
Paris Inra-muros has a balanced distribution of sensors.
However, there is a concentration of citizen sensors to the north-west in the commune of Colombes and to the north in the commune of St-Ouen (between Clichy and St-Denis). This phenomenon could reflect either a concern on the part of citizens, or/and the presence of a group of citizens sharing a curiosity about their environment.
Sensors in and around Paris
Complementary “citizen sensor” and “official sensor"
The cohabitation of official and citizen sensors is an asset for obtaining a broader and more complete picture of air quality over an area as varied as Paris. It also makes it possible to calibrate citizen sensors to consolidate consistency in measurements.
The difference between citizen sensors and official sensors
Official sensors are generally installed at ground level, whereas citizen sensors, set up in the place of one’s choice, can be several meters above ground (e.g. 6th floor of a building), and their measurement is different from that of a sensor that would be at ground level.
On the other hand, the citizen sensor, by design, measures a number of particles in suspension, which is then transformed into equivalent mass (micrograms per m3), whereas the official sensor directly measures a mass of particles in suspension.
These differences in operation are reflected in the readings from each sensor (figure opposite), showing a difference in assessment in the event of pollution peaks. However, this particularity is not a handicap when all measurements are integrated over a given period to obtain an average value (e.g. over a month) giving a similar value for both types of sensor, since pollution peaks are not a long-term situation. The detection of accentuated pollution peaks is therefore an asset for identifying specific particle-generating events.
Example of a citizen sensor (red ID 59846) with an official sensor (blue RP75022)
Both sensors show a measurement peak between July 13 and 14, corresponding to the fireworks during the July 14 festivities; the citizen sensor shows twice the sensitivity of the official sensor, although its behavior is similar over the rest of the period; the dynamics of the two sensors are equivalent, with the general discrepancy stemming from the different positions of the two sensors, the official sensor being located near a busy thoroughfare, while the citizen sensor is on a more residential street.
Overall view of measurement results for the Paris region in July 2024
After processing the various sensors providing operational values, and using the full month’s readings, a concentration map can be drawn up for each type of concentration.
The figures shown give the concentration of the type of particles concerned in micrograms per m3 (refer to the information on the home page for the color code).
PM 10
Paris and surrounding area
Paris center
PM 2.5
Colombes PM10 zone
(North-West Paris)
St-Ouen PM10 zone
(North Paris)
Colombes PM2.5 zone
(North-West Paris)
St-Ouen PM2.5 zone
(North Paris)
Overall balance
Official sensors, generally placed on major traffic lanes (inner and outer ring roads and major arteries), give high concentration values.
Citizen sensors located away from major traffic roads give tolerable average PM10 concentrations, but for long-term cumulative PM2.5 values above the recommended WHO standard.
Detailed measurements (see curves below) show a disturbed environment, with numerous pollution peaks, particularly in PM10.
Detailed measurements
Concentrations on the Paris ring road
Measurements on the Paris ring road reflect the highest concentrations encountered during this period; they are taken by official AirParif sensors and are therefore recognized by the authorities.
PM10 measurements
PM2.5 measurements
Concentrations in the center of Paris
The following graphs show measurements from all citizen sensors located in central Paris (inside the ring road). In comparison, the measurements of two official sensors (dotted lines) located in central Paris on busy thoroughfares are also plotted.
The average level of citizen sensors is within a +/- 20% variation range (which is reflected in the monthly average values shown above), with frequent high peaks corresponding to specific local events; in particular, high peaks appear on the evenings of July 13 and 14, corresponding to the festive events of the National Day.
A significant rise in values at the end of the month (particularly July 26-27-30 and 31) of between 30% and 100% compared with previous days could be due to the Olympic effect through a more restrictive traffic plan in Paris.
PM10 measurements
PM2.5 measurements
Specific behavior
Sensors located in the orange zone on the map opposite show a similar signature, particularly with regard to the measurement peaks observed in the evening of July 13 and 14. These peaks are also observed and marked on two official sensors (RP75021 operating solely in PM10 and RP75019 operating solely in PM2.5), showing that this phenomenon is not an anomaly of the citizen sensors.
Outside this zone, particularly to the south and south-east, the measurement peaks of July 13-14 faded very quickly, demonstrating that these peaks resulted from particle emissions originally in the center of Paris moving north-westwards under the effect of a light wind.
The graphs below show the similar behavior of these sensors even at other times of the month.
When citizens care ....
There are two areas in the Paris suburbs where the density of collectors is high: the commune of Colombes and the commune of St-Ouen, as presented above.
There is a reason for this:
- it means that in each of these communes, people are in touch (through a collective?) to better understand their environment,
- that an underlying concern has motivated their mobilization.
A detailed analysis of their sensors is interesting, and may provide a clue to their concerns.
Municipality of Colombes
Overall, the response of the sensors installed in the municipality is similar to an acceptable average value, particularly for PM10, but two sensors seem to give occasional significant concentration peaks. These two sensors are located on a major artery crossing the commune. An official sensor (red dotted line) located in the neighboring commune of Gennevilliers and close to the artery in question also shows significant concentration peaks. It is probably the high level of traffic on the arterial road in question, representing a substantial level of pollution on the official sensor, which is the reason for the concern of the inhabitants of this commune and their concern to monitor the phenomenon.
Municipality of St-Ouen sur Seine
The commune is close to the intersection of the A1 northern motorway and the Paris ring road, two of Europe’s busiest thoroughfares. The official sensor (RP75005 in dotted red on the graphs opposite) shows a disturbed and polluted environment.
Here too, two citizens’ sensors (referenced on the graphs) regularly show significant pollution peaks; these two sensors are located on either side of an intersection in the town center, one of the roads is at a freeway exit and crosses the commune. However, five other sensors located at medium distance along the same axis do not seem to show similar peaks. This may be due to their location further back from the traffic lane and away from the intersection; furthermore the intersection amplifies the effects of particulate emissions through braking and starting, which can be penalizing in heavy traffic.
So it’s easy to understand why people are so concerned about the deterioration in air quality, and how they’re trying to control it themselves.
Dynamic presentation of measurement points
To better interpret the measurement curves and their evolution at each location, a dynamic presentation of the air quality measurement over the study area is better suited to showing the evolution of particle pollution both geographically and over time.
PM10 concentration trends in the overall Paris area
Visualization
PM10 and PM2.5 in Paris
The two videos opposite show the environment considered over the period July 1 to July 31, 2024. The accelerated speed corresponds to approximately 4 hours every second.
All valid measurement points (AirParif sensors and citizen sensors) are taken into account in these simulations.
PM2.5 concentration trends in Paris and its inner suburbs