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Olten, nestled in the canton of Solothurn, Switzerland, occupies a strategically important, yet geographically complex, position within the Swiss Plateau. The city straddles the confluence of the Aare and Limmat rivers, a location historically vital for trade and transport, but also influencing local air quality. Situated at an elevation of approximately 430 meters (1,410 feet), Olten is surrounded by rolling hills and agricultural land, transitioning to more mountainous terrain further south. This topography creates a natural bowl effect, potentially trapping pollutants during periods of atmospheric stability. The city itself is a significant railway hub, a key node in Switzerland’s extensive rail network, contributing to localised emissions from train traffic. While not heavily industrialised, Olten benefits from proximity to industrial areas in the larger Basel and Zurich regions, meaning long-range transport of pollutants is a factor. The urban-rural gradient is relatively sharp; immediately surrounding the city are predominantly agricultural fields, with denser forest cover on the higher ground. This mix of land use impacts the dispersion of pollutants, with agricultural activities contributing to ammonia emissions and forests influencing particulate matter levels. The river valleys act as conduits for air movement, but can also channel pollutants, exacerbating air quality issues during calm conditions.

Olten’s air quality follows a distinct seasonal pattern. Winter, from December to February, often sees the poorest air quality due to temperature inversions. Cold, dense air becomes trapped in the valley, preventing the dispersal of pollutants from heating systems and traffic. Wood burning for heating, common in Switzerland, significantly contributes to particulate matter during these months. Spring (March-May) brings gradual improvement as temperatures rise and atmospheric mixing increases, though pollen levels become a concern for allergy sufferers. Summer (June-August) generally offers the cleanest air, with prevailing winds effectively dispersing pollutants and rainfall acting as a natural scrubber. However, increased ozone formation can occur during prolonged periods of sunshine and high temperatures. Autumn (September-November) sees a return to poorer conditions as heating demand increases and atmospheric stability returns. Fog, frequent in the autumn and winter, further exacerbates pollution by trapping pollutants near the ground. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter inversions and periods of high pollen counts in spring. Monitoring forecasts and adjusting activity levels accordingly is crucial for protecting health.