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Berre-l’Étang, nestled in the Provence-Alpes-Côte d'Azur region of France, occupies a unique and geographically sensitive position. The city’s name derives from its proximity to Étang de Berre, a large lagoon – the largest in France – which significantly influences the local climate and air quality. Situated at approximately 43.4760° N, 5.1686° E, Berre-l’Étang lies on a relatively flat plain, averaging around 20 meters above sea level, bordering the lagoon and transitioning into gently rolling hills towards the north and west. This low-lying terrain, combined with the lagoon’s presence, creates a basin-like effect, often trapping pollutants and exacerbating temperature inversions. The surrounding landscape is a mix of agricultural land – primarily vineyards and olive groves – and industrial zones concentrated along the Étang de Berre’s shores, particularly to the east. Marseille, a major industrial and port city, lies approximately 25 kilometers to the southeast, contributing to regional air pollution that can impact Berre-l’Étang. The urban–rural gradient is gradual, with smaller villages and agricultural areas interspersed throughout the region. The lagoon itself acts as a thermal regulator, moderating temperatures but also potentially contributing to humidity and fog formation, which can impede pollutant dispersion. The proximity to the Rhone River delta further influences the regional weather patterns and potential for pollutant transport. The geological composition of the area, largely alluvial deposits, also affects drainage and potential for localized flooding, which can impact air quality through the release of trapped pollutants.

Berre-l’Étang experiences a Mediterranean climate, resulting in distinct seasonal patterns affecting air quality. Summers (June-August) are typically hot and dry, with minimal rainfall and strong sunshine. This often leads to stagnant air conditions, particularly during prolonged heatwaves, as the basin effect traps pollutants emitted from local agriculture (pesticide drift) and nearby industrial activity. Temperature inversions are common during these months, where a layer of warm air sits above cooler air near the ground, preventing vertical mixing and concentrating pollutants. Autumn (September-November) brings a slight improvement as winds increase and rainfall returns, helping to disperse accumulated pollutants. However, agricultural burning practices, while regulated, can still contribute to particulate matter during this period. Winters (December-February) are generally mild and wet, with frequent fog formation over the Étang de Berre. This fog, while visually striking, significantly reduces air quality by trapping pollutants close to the ground. The lagoon’s surface temperature also influences local humidity, further contributing to fog. Spring (March-May) offers the most favourable conditions, with increasing wind speeds and rainfall, leading to improved air quality. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the summer months and periods of dense fog. Outdoor activities are generally best enjoyed during spring and autumn, avoiding peak agricultural burning times in autumn. Monitoring local weather forecasts for temperature inversions and fog is crucial for informed decision-making regarding outdoor exposure.