Modeling of atmospheric transfers of pollutants - Operational elements

The quality of the air we breathe every day is essential to a healthy lifestyle. The notion of air quality and the associated phenomenon of atmospheric pollution have been studied for a very long time. As early as the 4th and 5th centuries B.C., Hippocrates stressed in his treatise on "Airs, Waters and Places" that anyone wishing to study medicine in depth must examine "which are the hot and cold winds, especially those common to all countries, then those peculiar to each locality". In this way, Hippocrates set out to show that diseases, which seem to bear no resemblance to one another, have one and the same vector: the air we breathe.

Today, in the context of any activity - industrial, agricultural, natural or other - that emits atmospheric pollutants, it is necessary to assess the fate of these pollutants and their impact on human health and exposed ecosystems. These studies are generally carried out as part of risk assessments for planned or chronic exposure, and hazard or safety assessments for accidental situations. This type of study is a regulatory obligation, and forms part of the authorizations submitted to the relevant authorities, notably for the proper operation of industrial installations of the ICPE (installation classée pour la protection de l'environnement) or INB (installation nucléaire de base) type.

Risk and hazard assessments are based on modeling the atmospheric dispersion of effluent discharges, either emitted via dedicated outlets (e.g. factory chimneys), or emitted in an uncontrolled manner in the event of an accident. The aim is to estimate the exposure of populations and ecosystems to the pollutants released, either externally (exposure to the plume and surface deposits) or internally (exposure by inhalation or ingestion).

Normal and accidental situations are clearly differentiated, as they have different objectives. In normal situations, the aim is to demonstrate that there is no risk of exposure to routine releases from the facility. Every release is accompanied by a monitoring program at the outfall (release control) and of the quality of the air and exposed media (soil, plants, farm produce, etc.), to ensure that there is no impact on the populations and ecosystems in the vicinity of the facility. In the event of an accident, it is important to demonstrate that the facilities and preventive measures are correctly sized to avoid any unacceptable risk, following an event of internal origin such as a fire, or external origin such as an extreme climatic event.

The study of pollutant dispersion can also be carried out as part of specific studies, such as the sizing of an outfall, the study of the effect of buildings or relief on a complex site, or diffuse pollution in an urban environment....