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Mérignac, situated in the Nouvelle-Aquitaine region of southwestern France, presents a unique geographic context influencing its air quality. Located just southwest of Bordeaux, at coordinates 44.8386, -0.6436, the city occupies a relatively flat terrain, part of the broader Garonne plain. This plain, historically marshland, has been drained for agriculture and urban development. The elevation is low, generally under 20 meters, contributing to potential temperature inversions that trap pollutants. The proximity to the Garonne River, while providing a vital waterway, also introduces humidity which can affect pollutant dispersion. Mérignac’s urban character is a blend of residential areas, light industrial zones – particularly related to aerospace – and green spaces. Surrounding Mérignac are extensive vineyards, pine forests (the Landes forest to the west), and agricultural land. The urban-rural gradient is relatively sharp, with rapid transitions from dense housing to open countryside. The Bordeaux-Mérignac airport is a significant source of localised emissions. The prevailing winds, often from the Atlantic, can transport pollutants from the coast inland, while calm conditions can lead to pollutant build-up, especially during periods of high pressure. This interplay of geography and human activity shapes the city’s air quality profile.

Mérignac’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees a rise in particulate matter due to agricultural activities – tilling fields and spreading fertilizers – combined with increasing temperatures and potential for stagnant air. Pollen levels are also high, impacting respiratory health. Summer (June-August) generally offers the best air quality, benefiting from prevailing Atlantic breezes that disperse pollutants and higher mixing heights. However, heatwaves can exacerbate ozone formation, a secondary pollutant. Autumn (September-November) brings a return of poorer air quality as heating systems are switched on, increasing emissions from wood burning and fossil fuels. Fog, common during this season, can trap pollutants near the ground. Winter (December-February) is typically the period of highest pollution, driven by increased heating demand, temperature inversions, and reduced sunlight hindering pollutant breakdown. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these colder months. Monitoring wind direction is crucial; winds from the east can bring pollutants from the industrial areas of Bordeaux. Avoiding peak hours near the airport is also advisable.