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Tonoshō, nestled in the heart of Kagawa Prefecture on the island of Shikoku, Japan, presents a fascinating case study in urban geography and its influence on air quality. Situated at approximately 34.48°N, 134.18°E, the city occupies a relatively low-lying coastal plain, averaging around 15 meters above sea level. This proximity to the Seto Inland Sea significantly moderates temperatures and introduces a maritime influence on weather patterns, but also presents potential for sea salt aerosol deposition. Tonoshō’s terrain is gently undulating, characterized by rice paddies and small-scale agricultural fields, reflecting the prefecture’s strong agricultural heritage. The surrounding landscape is predominantly rural, transitioning from cultivated fields to forested hills further inland. Kagawa Prefecture is part of the broader Chūgoku region, and Tonoshō lies within a zone experiencing a gradual urban–rural gradient, with larger urban centers like Takamatsu located a short distance to the east. While Tonoshō itself is a small city, its location within a region experiencing moderate industrial activity—particularly related to food processing and manufacturing—means it is not entirely isolated from potential pollution sources. The prevailing winds, generally southwesterly, can transport pollutants from industrial areas to the north and west. The city’s compact urban footprint, combined with the surrounding agricultural land, creates a unique microclimate that can trap pollutants under certain meteorological conditions, impacting local air quality.

Tonoshō’s air quality experiences a distinct seasonal cycle dictated by Japan’s monsoon climate. Spring (March-May) brings mild temperatures and increased rainfall, generally leading to improved air quality as precipitation washes away particulate matter. However, the arrival of *pollen* during this period can significantly impact respiratory health, particularly for those with allergies. Summer (June-August) is characterized by hot, humid conditions and the potential for stagnant air, especially during periods of high pressure. While rainfall is frequent, the high humidity can trap pollutants close to the ground. Autumn (September-November) often sees the most challenging air quality conditions. The transition from summer to winter can bring periods of temperature inversions, where a layer of warm air traps cooler air and pollutants near the surface. This, combined with agricultural burning practices in surrounding rural areas, can lead to elevated levels of particulate matter. Winter (December-February) is typically the driest season, with cold temperatures and occasional fog. While the cold can reduce the formation of some pollutants, fog can trap existing pollutants, creating localized episodes of poor air quality. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit outdoor activity during periods of stagnant air or fog, particularly in autumn. Monitoring local weather forecasts and being aware of agricultural burning schedules can help individuals make informed decisions about outdoor exposure.