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Tsuruga, nestled on the coast of the Sea of Japan in Fukui Prefecture, Japan, occupies a geographically significant position within the broader context of Honshu’s central region. The city’s terrain is characterized by a gradual slope from the coastal plains towards the forested hills inland, a typical feature of the Sea of Japan side of Japan. Elevation ranges from sea level along the coast to approximately 200 meters in the surrounding hills. This coastal location profoundly influences Tsuruga’s climate and, consequently, its air quality. The Sea of Japan itself moderates temperatures, but also contributes to high humidity and frequent cloud cover, a key factor in trapping pollutants. The surrounding landscape is predominantly rural, comprising rice paddies, small-scale agriculture, and extensive coniferous forests. While Tsuruga itself is a relatively small city, it historically served as a vital port, and remnants of this maritime heritage are evident in its urban character. The urban gradient transitions smoothly into the rural landscape, with residential areas blending into agricultural fields. There are no major industrial belts immediately adjacent to Tsuruga; however, larger industrial zones are located further inland, potentially impacting air quality through long-range transport of pollutants. The prevailing winds, often originating over the Sea of Japan, can carry moisture and particulate matter inland, impacting local air quality. The city’s location within a basin-like topography can also exacerbate the effects of temperature inversions, trapping pollutants near the ground, particularly during colder months. The proximity to the Sea of Japan also means that sea salt aerosols contribute to the particulate matter composition.

Tsuruga’s air quality experiences a distinct seasonal cycle heavily influenced by its maritime climate and regional weather patterns. Winter (December-February) presents the most challenging period. Cold air masses originating from Siberia frequently settle over the region, leading to temperature inversions where a layer of warm air traps cooler air and pollutants near the ground. This, combined with limited wind circulation due to high-pressure systems, results in stagnant air and a potential build-up of particulate matter. Fog, common during these months, further reduces visibility and can exacerbate respiratory issues. Spring (March-May) brings a gradual improvement as temperatures rise and winds increase, dispersing pollutants. However, the ‘yellow dust’ phenomenon, originating from the Gobi Desert, can occasionally impact air quality, depositing fine particulate matter. Summer (June-August) generally sees the best air quality due to strong southwesterly monsoon winds that effectively flush out pollutants. Humidity is high, but the frequent rainfall helps to cleanse the atmosphere. Autumn (September-November) marks a transitional period. While winds remain relatively strong, cooler temperatures and occasional high-pressure systems can lead to periods of stagnant air. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during winter months, limiting outdoor activity on days with persistent fog or calm conditions. During the yellow dust season, wearing a mask can provide some protection. Staying informed about local weather forecasts and air quality reports is crucial for making informed decisions about outdoor activities throughout the year.