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Sélestat, nestled in the Grand Est region of France, occupies a strategic position within the Alsace plain, at coordinates 48.2594° N, 7.4542° E. The city’s geography is defined by its location at the foot of the Vosges Mountains, and its proximity to the Rhine River, approximately 15km to the east. This relatively flat terrain, at an elevation of around 185m, facilitates the dispersal of air masses, but also creates conditions conducive to temperature inversions, particularly during stable atmospheric periods. Sélestat’s urban character is a blend of medieval heritage and modern development, with a compact city centre surrounded by expanding residential areas. The surrounding landscape is predominantly agricultural, featuring extensive arable land and vineyards, alongside pockets of forested areas on the lower slopes of the Vosges. While Sélestat isn’t directly within a major industrial belt, its regional connectivity means it experiences some influence from industrial activity in nearby areas. The urban-rural gradient is relatively sharp, transitioning quickly from built-up areas to open farmland. This proximity to agricultural zones introduces potential sources of particulate matter from farming activities, while the Rhine valley can channel pollutants from further afield. The prevailing westerly winds play a crucial role in air quality, influencing pollutant transport and dispersion.

Sélestat’s air quality follows a distinct seasonal pattern. Winter, from December to February, often sees the poorest air quality. Cold, stable air masses combined with increased wood burning for heating create conditions for temperature inversions, trapping pollutants near the ground. Low wind speeds exacerbate this issue. Spring (March-May) brings gradual improvement as temperatures rise and wind patterns become more dynamic, dispersing pollutants. However, agricultural activities, such as fertilizer application, can contribute to ammonia and particulate matter levels. Summer (June-August) generally offers the best air quality, with warm temperatures, higher wind speeds, and increased atmospheric mixing. However, occasional heatwaves can lead to ozone formation, a secondary pollutant. Autumn (September-November) sees a decline in air quality as heating demand increases and atmospheric stability returns. Fog, common during autumn mornings, can trap pollutants and reduce visibility. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter and autumn mornings. Monitoring pollen levels is also important during spring and summer. Months to favour for outdoor activity are June, July and August, while December, January and February require greater caution.