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Castelginest, nestled in the Occitanie region of southwestern France, occupies a gently undulating landscape approximately 8km south of Toulouse. The city’s elevation, around 160m, contributes to a mild climate but also influences local air circulation patterns. Situated within the Garonne River valley, Castelginest benefits from the moderating influence of the river, though this also creates potential for temperature inversions, trapping pollutants during calm weather. Historically an agricultural area, Castelginest has experienced significant suburban expansion linked to the growth of Toulouse, becoming a bedroom community. This transition has introduced increased traffic and domestic heating emissions. Surrounding the city are agricultural lands, primarily dedicated to cereal crops and vineyards, alongside pockets of light industry associated with the Toulouse aerospace cluster. The urban-rural gradient is relatively sharp, with farmland quickly giving way to residential areas. The proximity to Toulouse, a major industrial and transport hub, is a key factor impacting Castelginest’s air quality, as pollutants can be transported by prevailing winds. The terrain, while not mountainous, offers limited natural dispersion of pollutants, particularly during stable atmospheric conditions. Understanding these geographical factors is crucial for assessing and mitigating air pollution risks in Castelginest.

Castelginest’s air quality follows a distinct seasonal pattern. Winter, from December to February, typically sees the highest pollution levels. Reduced sunlight hours, increased reliance on wood-burning stoves for heating, and stable atmospheric conditions – often involving temperature inversions – contribute to particulate matter accumulation. Calm winds exacerbate the issue, trapping pollutants near ground level. Spring (March-May) brings improvement as temperatures rise and rainfall increases, washing away accumulated pollutants. However, agricultural activities, including fertilizer application, can introduce ammonia into the atmosphere. Summer (June-August) generally offers the cleanest air, with strong winds and convective activity dispersing pollutants. However, ozone formation can be a concern during prolonged periods of hot, sunny weather. Autumn (September-November) sees a gradual deterioration in air quality as heating demand increases and atmospheric stability returns. October and November are often marked by foggy conditions, which can trap pollutants. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter and periods of high ozone in summer. Monitoring pollen levels is also important during spring and summer. Avoiding peak traffic hours can further reduce exposure.