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Toulouse, known as the 'Pink City' for its distinctive terracotta brick architecture, occupies a strategic position in southwestern France's Occitanie region, nestled within the broad Garonne River valley. Situated at approximately 150 meters above sea level, the city lies at the confluence of the Garonne and its tributary the Touch, creating a relatively flat urban basin surrounded by gentle hills to the north and south. This topographic setting significantly influences air quality, as the valley can trap pollutants under stable atmospheric conditions, particularly during temperature inversions. Toulouse serves as the economic and cultural hub of the Midi-Pyrénées basin, with its urban character blending historic medieval quarters with modern aerospace industries concentrated in its northwestern suburbs. The city's location places it within a transitional zone between the Atlantic coastal influences to the west and Mediterranean climatic patterns to the east, creating complex wind patterns that alternately disperse or concentrate pollutants. Surrounding the urban core, the landscape transitions rapidly to agricultural plains dedicated to sunflower and cereal cultivation, while to the south, the foothills of the Pyrenees mountains create a natural barrier that can limit pollutant dispersion during certain weather conditions. The urban-rural gradient is pronounced, with dense central districts giving way to suburban sprawl and then open farmland within just 15-20 kilometers, though this proximity to agricultural areas can contribute to seasonal particulate matter from farming activities. Toulouse's position along major transportation corridors between the Atlantic coast and Mediterranean Sea further adds to its pollution burden from road traffic, while its status as Europe's aerospace capital brings specialized industrial emissions.

Toulouse experiences distinct seasonal variations in air quality driven by its transitional climate between oceanic and Mediterranean influences. During winter, typically from December through February, cold temperatures and frequent temperature inversions create stagnant conditions in the Garonne Valley, trapping pollutants from heating systems and vehicle emissions near ground level. These inversions, where warmer air sits above cooler surface air, prevent vertical mixing and can lead to elevated particulate matter concentrations, making mornings particularly problematic for sensitive groups. Spring brings improvement as increasing solar radiation and more frequent Atlantic weather systems enhance atmospheric mixing, though March and April can see occasional peaks from agricultural burning and pollen combined with urban emissions. Summer months, especially July and August, present a complex picture with generally good dispersion from thermal convection and prevailing northwesterly winds, but ozone formation becomes significant during heatwaves when intense sunshine reacts with nitrogen oxides and volatile organic compounds from traffic. These photochemical episodes typically peak in afternoon hours, advising sensitive individuals to limit strenuous outdoor activities during these periods. Autumn sees a gradual deterioration as temperatures cool and atmospheric stability increases, with October and November often experiencing pollution accumulation from vehicle emissions mixed with agricultural residue and reduced dispersion under anticyclonic conditions. Throughout the year, Toulouse benefits from occasional strong winds like the Autan blowing from the southeast or Atlantic systems from the west that provide natural ventilation, but during prolonged high-pressure periods, the city's basin geography can lead to multi-day pollution episodes requiring precautionary measures for children, elderly, and those with respiratory conditions.