Hourly forecasts to better anticipate
Pollution levels vary throughout the day (morning and evening rush hours, in the middle of the night, etc.). They also vary from place to place. The air we breathe is different near traffic, in a garden, on one side of a street to the other, etc.
To better anticipate your travels, the maps now inform you of the air quality to which you are exposed live and for the next 6 hours everywhere in Île-de-France.
Like weather forecast sites, our maps are updated every hour!
What do the maps show?
For each hour, a map represents the expected pollution level for each regulated pollutant: ozone (O3), nitrogen dioxide (NO2) and particles (PM10 and PM2.5). Another map also shows the global index synthesizing the data of the concentrations of these pollutants.
At what resolution?
These maps are outputs from digital tools capable of predicting pollution in the coming hour. They offer a resolution of around 10 meters in Paris, 25 meters in the departments constituting the inner suburbs (departments 92, 93, 94) and 50 meters in the outer suburbs (departments 77, 78, 91 and 95), i.e. 6 calculation points used to map the entire region.
How are they made?
This calculation chain is based on a "statistical emulator", a learning model based on a neural network, capable of reproducing what a "deterministic" model would have calculated (i.e. a model which explicitly solves the equations of atmospheric physics and chemistry) with equivalent input data (background concentration levels, meteorology, road traffic, time of day).
The forecasts from this emulator are then improved by integrating the data observed at the measurement stations via data assimilation methods. Since it is not possible to know in advance the observations for the next six hours, another machine learning model anticipates the measurements that the stations will record in the coming hours, thus making it possible to adjust the maps according to this predicted data.
Finally, an additional module ensures the consistency of these maps with the daily forecasts established by Airparif experts.
This calculation chain thus combines:
- data produced by different deterministic models:
ESMERALDA to describe the concentration levels in background situations (far from pollution sources)
MM5/CALMET for weather conditions,
COPERNIC to predict future concentrations at stations, - observed data from the Airparif network of measuring stations,
- and the expertise of Airparif forecasters,
ensuring realistic and reliable maps.
How do they differ from the old “real-time maps”?
Previously released maps, "real-time maps", presented the pollution of the current hour as well as the history of the last seven days. The modeling system was based on the physical and chemical model of the atmosphere called ADMS-Urban. This model combines meteorological data, traffic information and background pollution measurements to estimate pollution levels. Airparif's observations were then integrated in order to make the maps produced more faithful to reality. Due to limitations in computing time and memory, the "real-time maps" system cannot assess air quality for the next 6 hours in the desired times. To get around this constraint, Airparif has developed an emulator, capable of reproducing what ADMS-Urban would calculate with the same input data.
Disclaimer
It is important to note that these maps do not take into account specific events such as works, demonstrations, accidents, etc. which may occasionally and suddenly change traffic conditions as well as the concentration levels of pollutants on the roads concerned.
The index presented here differs from the daily ATMO index presented on the Forecast page, which is an index of overall exposure in a background situation and which allows you to understand what you are exposed to on average over the whole day and at the municipal resolution.
Monitoring of exceedances of hourly and daily regulatory thresholds at measuring stations
You can find the counter for thresholds exceedances by pollutant (hourly and daily) at the stations for the current year, not to be confused with the triggering of the information and alert procedure which are measured in relation to a criterion of surface area and population over the whole Île-de-France region.
- Download the file for the current year - PDF - approximately 25 KB per file (for nitrogen dioxide NO2, for ozone O3, for PM10 particles et for fine particles PM2,5 )