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Aarhus, Denmark's second-largest city, occupies a strategic position on the east coast of the Jutland peninsula, nestled around the natural harbour of Aarhus Bay. The city's geography is characterized by gently rolling hills, with the highest point reaching just 105 meters above sea level, creating a subtle but influential terrain that affects local air circulation. Situated within the Capital Region, Aarhus serves as the cultural and economic hub of central Jutland, with its urban character blending historic architecture with modern development. The city's location on the Kattegat sea provides maritime influences that typically help disperse pollutants, though the surrounding landscape—a mix of agricultural zones to the west and forested areas to the south—creates a distinct urban–rural gradient. Proximity to the bay means sea breezes can mitigate pollution, but the sheltered nature of the harbour also allows emissions from port activities and vehicle exhaust to accumulate under certain conditions. The city's expansion has led to increased construction dust and traffic, particularly around the university district, while residential heating in suburban areas adds to particulate matter. The flat coastal plain and lack of significant industrial belts nearby mean pollution is primarily urban-generated, with local topography occasionally trapping pollutants during calm weather, especially in low-lying areas near the waterfront.

In Aarhus, air quality follows a clear seasonal pattern influenced by its marine west coast climate. During winter, particularly from November through January, pollution peaks due to a combination of factors: increased residential heating emissions, higher vehicle use in darker months, and frequent temperature inversions that trap pollutants near the ground. Cold, stagnant air and reduced wind speeds exacerbate the buildup of particulate matter from road dust and exhaust. Spring brings gradual improvement as temperatures rise and winds from the Kattegat increase dispersion, though construction activities may spike dust levels. Summer offers the cleanest air, with long daylight hours, stronger sea breezes, and lower heating needs; however, occasional heatwaves can elevate ozone levels, and university traffic persists. Autumn sees a return to deteriorating conditions as heating systems activate and weather becomes more unsettled, with storms and flooding occasionally washing pollutants into waterways. Sensitive groups, such as those with respiratory issues, should avoid prolonged outdoor exposure during winter peaks and monitor air quality forecasts. The best months for outdoor activities are typically May through August, when dispersion is optimal and pollution sources are minimized. Fog, common in cooler months, can further trap pollutants, making early mornings in winter particularly hazardous for vulnerable populations.