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Caen, nestled in the heart of Normandy, France, occupies a geographically strategic yet complex position influencing its air quality. Situated approximately 15km inland from the English Channel, at coordinates 49.1814, -0.3636, the city benefits from a temperate oceanic climate but is also susceptible to coastal weather patterns. The terrain is relatively flat, part of the Pays d'Auge, a landscape characterised by rolling hills and agricultural land, transitioning to more urbanised areas closer to the city centre. Caen is bisected by the Orne River, which provides a natural corridor for air movement but can also trap pollutants during temperature inversions. Historically, Caen’s industrial activity was concentrated along the riverbanks, though much has transitioned to service industries. Surrounding Caen are extensive agricultural zones, particularly dairy farming, contributing to ammonia emissions. The urban-rural gradient is relatively sharp, with farmland immediately bordering the city limits. This proximity means Caen is directly impacted by agricultural practices and the transport of agricultural products. The prevailing winds, generally from the southwest, carry pollutants from the Atlantic and surrounding agricultural areas, while easterly winds can bring continental air masses. The city’s location within a river valley and near the coast creates unique microclimatic conditions that affect pollutant dispersion.

Caen’s air quality follows a distinct seasonal pattern. Winter (December-February) typically sees the poorest air quality, driven by increased residential heating using wood and fossil fuels, coupled with frequent temperature inversions trapping pollutants near the ground. Calm, damp conditions exacerbate particulate matter concentrations. Spring (March-May) brings a gradual improvement as temperatures rise and heating demand decreases, though agricultural activity increases, potentially raising ammonia levels. Summer (June-August) generally offers the cleanest air, benefiting from prevailing winds dispersing pollutants and increased rainfall washing them away. However, heatwaves can trigger ozone formation, a secondary pollutant. Autumn (September-November) sees a return to poorer conditions as heating begins again and agricultural activities like harvesting contribute to dust and emissions. Sensitive individuals – children, the elderly, and those with respiratory conditions – should be particularly cautious during winter and autumn. Fog, common in the Orne valley, can also trap pollutants, reducing visibility and worsening air quality. Months to favour for outdoor activity are June, July and August, but even then, monitoring conditions is advisable. Avoiding strenuous activity during peak heating periods in winter is recommended.