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Lyon, France's third-largest city, occupies a strategic position at the confluence of the Rhône and Saône rivers in the Auvergne-Rhône-Alpes region, creating a distinctive urban geography that profoundly influences its air quality. Situated within the Rhône Valley, Lyon is flanked by the Massif Central to the west and the Alps to the east, forming a natural corridor that channels air masses and pollutants. The city's elevation ranges from approximately 162 to 305 meters above sea level, with its urban core nestled in the valley floor, while surrounding hills like Fourvière and Croix-Rousse create microclimates and trap emissions. Lyon's location in one of Europe's major industrial belts, historically centred on textiles and chemicals, contributes to persistent industrial emissions, compounded by dense road networks and vehicle exhaust. The Rhône Valley acts as a pollution trap, particularly during temperature inversions in winter, when cold air settles in the valley, preventing the dispersion of pollutants from residential heating, traffic, and nearby industrial zones. Proximity to agricultural areas in the surrounding plains adds occasional agricultural dust and burning residues. The urban–rural gradient sees higher pollution concentrations in the densely built central arrondissements, gradually decreasing toward the peri-urban fringes and green spaces like Parc de la Tête d'Or, though the valley's topography limits effective ventilation, making Lyon's air quality challenges inherently geographic.

Lyon's air quality follows a distinct seasonal pattern shaped by its marine west coast climate and topographic constraints. In winter, particularly from December to February, pollution peaks due to temperature inversions in the Rhône Valley, where cold, stagnant air traps emissions from residential heating, vehicle exhaust, and industrial sources, leading to elevated particulate matter levels; sensitive groups such as children, the elderly, and those with respiratory conditions should limit outdoor activities during these months. Spring brings gradual improvement as increased sunlight and warmer temperatures enhance atmospheric mixing, though occasional storms can stir up road and construction dust, making March and April moderately polluted. Summer sees lower pollution levels overall, with prevailing westerly winds dispersing pollutants, but heatwaves in July and August can exacerbate ozone formation from vehicle emissions, posing risks for outdoor exercisers and asthmatics; this season is generally favourable for outdoor activities, especially in early morning or evening. Autumn transitions with cooler temperatures and reduced wind, leading to a buildup of pollutants by November, compounded by fog and reduced dispersion; October offers relatively clean air before winter sets in. Year-round, Lyon's weather hazards like heatwaves and storms intermittently affect air quality, but the winter inversion phenomenon remains the most significant meteorological factor driving seasonal pollution highs.