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Turku, situated in southwestern Finland’s Varsinais-Suomi region, is a coastal city profoundly shaped by its archipelago setting and the Aura River that bisects it. Located at 60.4517°N, 22.2669°E, the city’s terrain is relatively flat, typical of the Finnish coastal plains, with elevations rarely exceeding 50 meters. This low-lying landscape, combined with its proximity to the Baltic Sea, significantly influences local air quality. The sea provides a moderating effect on temperatures, but also contributes to humidity and potential for fog, which can trap pollutants. Historically, Turku was a significant industrial hub, with shipbuilding and manufacturing concentrated along the river and its estuary. While industry has diversified, remnants of these activities, alongside modern transport infrastructure (ports, roads, and a regional airport), contribute to localised emissions. Surrounding Turku is a gradient from urban density to rural landscapes dominated by agriculture and forests. The agricultural zones to the north and east can contribute to particulate matter from farming activities, while prevailing winds often carry pollutants from further afield, impacting the city’s air. The complex interplay of maritime influences, historical industrial activity, and surrounding land use creates a unique air quality profile for Turku.

Turku’s air quality follows a distinct seasonal pattern. Winter, from December to February, often sees poorer air quality due to temperature inversions – cold air trapped beneath warmer layers – preventing pollutant dispersion. Wood burning for heating, a common practice in Finland, significantly contributes to particulate matter (PM2.5 and PM10) during these months. March and April bring a gradual improvement as temperatures rise and snowmelt reduces reliance on wood stoves. However, road dust from sanding and gritting can temporarily elevate particulate levels. Summer, from June to August, generally offers the cleanest air, benefiting from prevailing westerly winds that flush out pollutants and increased atmospheric mixing. However, occasional heatwaves can lead to ground-level ozone formation. Autumn, particularly September and October, sees a return of wood burning as heating demand increases, coupled with calmer weather conditions, leading to a decline in air quality. Fog, common during autumn mornings, exacerbates pollution. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during prolonged periods of cold, still weather in winter and during foggy autumn days. Monitoring pollen levels is also crucial during spring and summer.