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Higashikagawa, nestled in Kagawa Prefecture on Shikoku Island, Japan, presents a fascinating case study in how geography shapes urban air quality. The city’s location along the Seto Inland Sea significantly influences its climate and pollution patterns. Characterized by a gently undulating terrain, Higashikagawa’s elevation rarely exceeds 100 meters, minimizing the potential for significant topographic trapping of pollutants. The surrounding landscape is predominantly rural, a patchwork of terraced rice paddies and citrus groves, a testament to the region’s agricultural heritage. This proximity to agricultural zones, while contributing to the area’s scenic beauty, can occasionally introduce biogenic volatile organic compounds (BVOCs) into the atmosphere, particularly during warmer months. Higashikagawa’s position within the Seto Inland Sea region means it experiences maritime influences, including sea breezes that generally disperse pollutants. However, the sea itself can also contribute to air quality challenges, with occasional salt spray and the potential for marine-derived particulate matter. The city’s urban footprint is relatively small, with a gradual urban–rural gradient extending outwards. While Kagawa Prefecture has some industrial activity, Higashikagawa itself is largely a residential and agricultural community, reducing the direct impact of heavy industrial emissions. The prevailing winds, typically from the southwest, play a crucial role in transporting air masses and influencing the city’s air quality, often bringing cleaner air from the mainland. The surrounding hills offer some shielding from winds originating from the north, potentially leading to localized stagnation under certain meteorological conditions.

Higashikagawa’s air quality exhibits a distinct seasonal rhythm dictated by its climate and prevailing weather patterns. Spring (March-May) generally sees improved air quality as temperatures rise and sea breezes become more frequent, effectively dispersing any accumulated pollutants. However, pollen season can significantly impact respiratory health, creating a different kind of air quality challenge. Summer (June-August) is typically the cleanest period, with consistent sea breezes and occasional rainfall helping to scrub the atmosphere. High temperatures, however, can exacerbate ozone formation, a secondary pollutant, particularly on stagnant days. Autumn (September-November) marks a transition period. While the sea breezes persist, the increased frequency of cooler, calmer days can lead to localized temperature inversions, trapping pollutants near the ground, especially in the mornings. Winter (December-February) presents the most challenging period for air quality. Cold, stable air masses often settle over the region, suppressing vertical mixing and promoting temperature inversions. Fog, common during these months, further reduces visibility and traps pollutants. Agricultural burning, though regulated, can also contribute to particulate matter levels. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter months, limiting outdoor activity on days with poor visibility or stagnant air. Spring pollen counts require careful monitoring and preventative measures. Overall, Higashikagawa’s air quality is generally good, but seasonal variations and localized meteorological conditions can significantly impact pollutant concentrations.