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Marugame, nestled in Kagawa Prefecture on the island of Shikoku, Japan, presents a unique geographic setting influencing its air quality. The city occupies a relatively flat coastal plain bordering the Seto Inland Sea, with a gentle slope rising towards the hills inland. This proximity to the sea moderates temperatures but also introduces the potential for sea breezes to transport pollutants. Marugame’s urban character is a blend of traditional Japanese architecture and modern development, typical of smaller Japanese cities. The surrounding landscape is predominantly agricultural, particularly rice paddies, interspersed with pockets of light industry. Kagawa Prefecture, and Marugame specifically, is not a major industrial hub like some other regions of Japan, which generally contributes to better baseline air quality. However, the presence of smaller manufacturing facilities and transportation corridors does introduce localised sources of pollution. The urban-rural gradient is relatively sharp, with agricultural land immediately surrounding the city centre. The terrain’s flatness can contribute to temperature inversions, trapping pollutants near the ground, particularly during calmer weather conditions. The Seto Inland Sea’s complex topography can also influence wind patterns, creating localised areas of stagnation and affecting pollutant dispersion. Understanding these geographical factors is crucial for assessing and mitigating air quality concerns in Marugame.

Marugame’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees increased particulate matter from agricultural burning as farmers prepare fields for planting, coupled with pollen from flowering trees. Winds can be variable, sometimes exacerbating pollution. Summer (June-August) brings the humid subtropical climate of Shikoku, with the rainy season initially offering some cleansing effect, washing pollutants from the air. However, stagnant air during periods of high humidity can trap pollutants. Autumn (September-November) is generally the period of best air quality, with cooler temperatures, clearer skies, and more consistent winds aiding dispersion. This is the most favourable time for outdoor activities. Winter (December-February) presents the most challenging conditions. Temperature inversions are common, trapping pollutants from heating sources and industrial activity near the ground. Dry, cold air also reduces the natural settling of dust and particles. Sensitive groups, including the elderly, children, and those with respiratory conditions, should limit strenuous outdoor activity during winter mornings. Fog, common in the Seto Inland Sea during winter, can further concentrate pollutants. Monitoring wind direction is key, as pollutants can accumulate if winds are weak or blow from industrial areas.