What is forecasting for?

This particularly important mission is carried out by a team of forecasters, who forecast every day the ATMO air quality index for the same day and the next day. This daily index represents your overall background exposure over the day, taking into account the following pollutants: Ozone (O₃), nitrogen dioxide (NO2), particles PM₁₀, sulfur dioxide (SO₂) and, since 1st January 2021, particles PM_2.5. This index has in fact had a facelift on this date, with a modification of the thresholds, consistent with the European index, and taking into account particles PM_2.5. 

Beyond the daily air quality bulletin, Airparif is tasked by the authorities, and in particular the Prefect of Police, with predicting and detecting pollution episodes. Airparif provides its expertise on: the origin of the episode, the pollutant(s) concerned, the number of people potentially impacted and the territories affected. Airparif also assesses future trends so that Ile-de-France residents are informed and appropriate measures can be implemented by the authorities to reduce the intensity of the peak. Forecasting pollution episodes concerns nitrogen dioxide, ozone and particles PM₁₀ (which also include the PM_2.5), in accordance with the information and alert procedure.
App, web, media, urban signs... these results are shared every morning and provide information to adapt one's activities: in particular to protect oneself and to reduce one's emissions in the event of a pollution episode.

How is it carried out?

As with the weather, it is possible to make an air quality forecast. This forecast, which is complex to produce, integrates numerous data and parameters.
It requires simultaneously taking into account the different elements involved in the formation of atmospheric pollution and evaluating their evolution during the day:

• Local and regional emissions, and the analysis of their origin (traffic, industry, heating, agriculture, etc.);
• Pollution transfers (for example ozone imported from other regions or the recirculation of air masses);
• Weather data;
• Transformations of pollutants in the air linked to physicochemical phenomena;
• Observations of measurements recorded by the stations.

Thus, every day, Airparif forecasters use their knowledge of air quality in Île-de-France, and also in terms of air chemistry and the behavior of pollutants in the atmosphere. The data from our measuring stations and French weather forecasts, provided daily by our partner Meteo France, but also European, are analyzed and compared to simulations of different models, in particular those of the interregional ESMERALDA platform managed by Airparif. At the end of these analyses, they issue a bulletin indicating the local air quality indices expected for the day and those for the next day, the maximum concentrations expected in the urban area for the main pollutants, and, if applicable, the forecast of a pollution episode and its origin. 

Did you know that more than 78% of index forecasts made by Airparif forecasters are accurate?

To learn more

• Sources of pollution

Pollutants can be of anthropogenic origin, that is to say produced by human activities, or of natural origin (emissions by vegetation, soil erosion, volcanoes, oceans, etc.). All sectors of human activity are likely to emit atmospheric pollutants: transport (road and non-road), industrial activities, domestic activities (heating in particular), agriculture, construction sites, etc.
However, not all pollutants observed in the atmosphere are emitted directly by these sources. For secondary pollutants, they also result from physicochemical reactions between chemical components present in the atmosphere, also linked to specific meteorological conditions.
Understanding pollution phenomena and their prediction thus requires a good knowledge of the sources of pollutants, their geographical distribution, and the quantities of pollutants emitted throughout the year, but also an interpretation in relation to the knowledge of developments on the short and medium-long term. These emissions can in fact vary significantly depending on the time of year, or even the time of day, but also over the years depending on the action plans that are implemented. 

• The link between air quality and meteorology

Air quality depends mainly on the intensity of polluting emissions, as well as on meteorology which significantly conditions their dispersion or accumulation in the atmosphere, as well as the formation of secondary pollutants. For the same level of pollution, meteorology can therefore play a dispersive or, on the contrary, aggravating role.