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Gaillac, nestled in the Occitanie region of southwestern France, presents a unique geographic setting influencing its air quality. The city sits within the Tarn department, approximately 50km east of Toulouse, and is characterized by a gently rolling landscape of vineyards and agricultural lands. The terrain is relatively flat, averaging around 160 meters above sea level, though subtle undulations are present due to the presence of ancient river terraces. The River Tarn flows nearby, providing a crucial hydrological element but also potentially contributing to humidity and localised temperature inversions. Unlike heavily industrialized areas, Gaillac’s surrounding landscape is predominantly rural, dominated by viticulture – the production of Gaillac wine being central to the local economy. However, the proximity to the Toulouse metropolitan area introduces a degree of regional air pollution transport. The urban-rural gradient is relatively sharp; the city itself is compact, transitioning quickly to open countryside. This means pollutants generated within Gaillac, primarily from domestic heating and road traffic, have limited dispersion, while the city is also susceptible to pollutants carried by prevailing winds from the larger urban centre to the west. The agricultural practices, including fertilizer use, can also contribute to ammonia emissions, impacting secondary pollutant formation.

Gaillac’s air quality follows a distinct seasonal pattern. Winter, from December to February, typically sees the poorest air quality. Low temperatures encourage the use of wood-burning stoves for heating, releasing particulate matter (PM2.5 and PM10) and carbon monoxide. Still, damp conditions and frequent temperature inversions trap these pollutants near the ground. Spring, March to May, brings improvement as temperatures rise and heating demand decreases, though agricultural activities begin, potentially increasing ammonia levels. Summer, June to August, generally offers the cleanest air, aided by prevailing winds and higher temperatures promoting pollutant dispersion. However, heatwaves can exacerbate ozone formation, a secondary pollutant. Autumn, September to November, sees a gradual decline in air quality as heating use increases again, coupled with the harvest season’s agricultural emissions. October and November are often marked by increased fog, which can trap pollutants. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter mornings and periods of fog. Monitoring pollen levels is also crucial in spring and summer. Avoiding peak traffic hours can further reduce exposure.