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Kemi, located in Pohjois-Pohjanmaa, Northern Ostrobothnia, Finland, occupies a unique and historically significant position within the Finnish landscape. Situated at 65.1333° N, 25.7750° E, the city rests on a coastal plain bordering the Bothnian Sea, a large arm of the Baltic Sea. This proximity to the sea significantly influences local weather patterns and, consequently, air quality. Kemi’s terrain is relatively flat, characterized by glacial till plains and numerous lakes and rivers, a typical feature of the region shaped by past ice ages. The surrounding landscape is a mosaic of boreal forests, peatlands, and agricultural fields, creating a distinct urban–rural gradient. While Kemi itself is a relatively small city with a population of approximately 13,320, it historically served as a crucial industrial hub, particularly for the pulp and paper industry, and still retains some industrial activity. This legacy contributes to localized pollution sources. The city’s location within a broader industrial belt along the Bothnian Sea, encompassing towns like Tornio and Kokkola, means that regional air quality can be affected by transboundary pollution. Elevation is minimal, rarely exceeding 30 meters above sea level, which can exacerbate temperature inversions during colder months, trapping pollutants near the ground. The prevailing winds generally blow from the west, carrying maritime air inland, but can shift, impacting the dispersal of emissions. The surrounding agricultural zones contribute to seasonal particulate matter from field activities.

Kemi’s air quality follows a distinct seasonal pattern dictated by its subarctic climate. During the long, dark winters (November to March), temperature inversions are common. Cold, dense air settles in the valleys and near the sea, trapping warmer air aloft and preventing vertical mixing. This phenomenon concentrates pollutants released from industrial sources and residential heating, primarily wood burning, leading to periods of reduced visibility and potentially elevated particulate matter. The lack of sunlight also limits photochemical reactions that would otherwise break down pollutants. Spring (April-May) brings a gradual improvement as temperatures rise and wind speeds increase, dispersing accumulated pollutants. However, agricultural activities, such as tilling and fertilizer application, can temporarily increase particulate and ammonia levels. Summer (June-August) generally offers the best air quality, with frequent winds and ample sunlight facilitating pollutant dispersion and breakdown. However, occasional stagnant weather patterns can still lead to localized pollution episodes. Autumn (September-October) sees a return to more challenging conditions as temperatures cool and the risk of temperature inversions increases, mirroring the winter pattern. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should be particularly cautious during the winter and autumn months, limiting outdoor exposure during periods of reduced visibility or noticeable odors. Avoiding strenuous outdoor activity during these times is advisable. The use of wood-burning stoves should be minimized, and proper ventilation is crucial in homes.