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Auch serves as the administrative heart of the Gers department within the Occitanie region, characterized by a gentle, undulating topography that defines the Gascon landscape. The city is strategically perched upon a plateau overlooking the valley of the Gers River, a positioning that creates a distinct urban-rural gradient where the dense, historic city center transitions rapidly into expansive agricultural hinterlands. This rolling terrain, composed of porous limestone and clay soils, is dominated by vast tracts of cereal crops, sunflowers, and vineyards, which play a pivotal role in the local atmospheric chemistry. Because Auch is situated in a valley-like setting, it is susceptible to localized air stagnation, particularly during periods of low wind speed, which can trap particulates near the ground. The proximity to the Atlantic Ocean ensures a temperate maritime influence, yet the inland position reduces the immediate cleansing effect of strong, cleansing sea breezes. There is a notable absence of heavy industrial belts, meaning that pollution sources are primarily decentralized and diffuse, stemming from vehicular traffic along regional transit corridors and agricultural emissions. The interaction between the elevated town center and the lower valley floor creates microclimates where cool air sinks, potentially concentrating pollutants during stable weather conditions. Consequently, the geographic character of Auch balances the purity of the rural countryside with the concentrated emissions of a small administrative hub, making its air quality highly dependent on the interplay between terrain-induced stability and regional wind patterns and the seasonal fluctuations of the surrounding lush Gascon farmland.

Air quality in Auch follows a distinct seasonal rhythm dictated by domestic habits and agricultural cycles. During winter, the city often experiences its most challenging periods; as temperatures drop, the prevalence of wood-burning stoves for heating increases, releasing fine particulate matter into the cool, stagnant air. This is frequently exacerbated by thermal inversions, where a layer of warm air traps pollutants in the Gers valley, leading to a buildup of haze that persists until a strong front clears the basin. Spring brings a transition, where air quality generally improves, though the rise in agricultural activity introduces ammonia and nitrates from fertilization, coinciding with high pollen counts that stress respiratory systems. Summer is characterized by intense solar radiation and high temperatures, which catalyze the formation of ground-level ozone. During these hot, dry months, stagnant high-pressure atmospheric systems can lead to ozone peaks, particularly in the afternoons, making it advisable for sensitive groups to avoid strenuous outdoor exercise between noon and six pm. Autumn typically offers the cleanest air, as increased rainfall washes particulates from the atmosphere and the cooling temperatures reduce ozone formation. However, the harvest season can trigger temporary spikes in dust and organic agricultural aerosols. For individuals with asthma or chronic obstructive pulmonary disease, the winter inversion months and peak summer ozone days are the most critical and dangerous periods for caution. By diligently monitoring regional alerts, residents can navigate these seasonal shifts, ensuring outdoor activities align with the natural cleansing and renewal cycles of the rustic Gascon climate.