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Rezé is strategically positioned on the southern bank of the Loire River, functioning as a vital residential and industrial satellite within the sprawling Nantes Métropole in western France. The city's geography is defined by its low-lying, predominantly flat alluvial terrain, which characterizes the river valley's transition toward the Atlantic coast. This flat landscape creates a seamless urban-rural gradient, where dense residential clusters blend into pockets of greenery and agricultural zones typical of the Pays de la Loire region. The proximity to the Loire is the primary geographic driver of its local climate and air quality dynamics. The river acts as a natural corridor, facilitating the movement of moist maritime air masses that generally help disperse pollutants. However, the city's location within the wider Nantes urban basin means it is subject to the cumulative emissions of a major metropolitan hub. To the east and south, the terrain remains largely open, allowing for the influx of rural air, yet the concentration of transport infrastructure—including critical arterial roads connecting the city center to the periphery—creates localized pollution hotspots. The interaction between the humid oceanic climate and the urban morphology of Rezé often leads to high humidity levels, which can trap particulate matter near the ground during stagnant weather periods. Consequently, the city's air quality is a complex interplay between the cleansing effects of the Atlantic breezes and the anthropogenic pressures of its deep industrial heritage and modern, heavy commuter traffic.

Air quality in Rezé follows a distinct seasonal rhythm dictated by the temperate oceanic climate of western France. During winter, the city often experiences its most challenging periods; the combination of increased residential heating and frequent temperature inversions traps nitrogen dioxide and fine particulates close to the surface, particularly during cold, windless mornings. This makes January and February the most sensitive months for asthmatics and the elderly, who should limit strenuous outdoor exertion during peak morning traffic. As spring arrives, the air generally clears due to increased wind speeds and rainfall, although the region sees a surge in biological aerosols and pollen, which can exacerbate respiratory distress for allergic populations. Summer brings a different challenge in the form of ground-level ozone. High solar radiation, coupled with precursors from urban traffic, triggers photochemical reactions that peak in July and August. During these heatwaves, air quality can degrade in the afternoons, necessitating precautions for sensitive groups. Autumn serves as a transitional phase where the return of humidity and morning mists can occasionally concentrate pollutants, though the overall air quality remains moderate. The prevailing westerly winds from the Atlantic generally act as a purifying force, sweeping away urban smog and maintaining a baseline of freshness. To optimize health, residents are encouraged to engage in outdoor activities during the mid-autumn or late spring windows, when the balance between temperature, wind dispersion, and low pollutant concentration is most favorable for respiratory health.