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Awaji, nestled in Hyogo Prefecture, Japan, occupies a unique geographic position as the largest island in the Inland Sea. Its terrain is predominantly hilly, rising to a maximum elevation of 338 meters at Mount Fuku, though coastal plains dominate much of the island’s perimeter. This topography significantly influences air quality, creating localized pockets of stagnant air, particularly in the valleys. The island’s location within the Seto Inland Sea moderates temperatures, but also limits natural ventilation, potentially trapping pollutants. Surrounding Awaji are the larger islands of Shikoku to the south and Honshu to the east, creating a complex interplay of air currents. While historically an agricultural region famed for its onions and citrus fruits, Awaji has seen increasing industrial development, particularly around the port areas, contributing to localised emissions. The urban-rural gradient is pronounced; the coastal cities and towns exhibit higher population density and associated pollution levels, while the inland areas remain largely rural. Proximity to major industrial hubs on Honshu, such as Osaka and Kobe, means Awaji can experience transboundary pollution events, impacting baseline air quality. The island’s coastal location also exposes it to marine aerosols, influencing particulate matter composition.

Awaji’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees increased particulate matter from long-range transport of dust storms originating in the Gobi Desert, exacerbated by prevailing westerly winds. Pollen from the island’s abundant vegetation also contributes to discomfort for allergy sufferers. Summer (June-August) brings the humid subtropical climate of the Inland Sea, with occasional typhoons that can temporarily improve air quality through strong winds and rainfall, but also disrupt settled dust. Autumn (September-November) is generally the clearest period, with stable high-pressure systems and cooler temperatures promoting dispersion. However, temperature inversions can occur, trapping pollutants near the ground. Winter (December-February) presents the most challenging conditions. Reduced sunlight and colder temperatures lead to increased use of heating fuels, raising levels of sulfur dioxide and particulate matter. Stagnant air masses, common during winter, exacerbate pollution build-up. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter months and periods of high pollen counts in spring. Monitoring wind direction is crucial, as pollutants from Honshu can significantly impact Awaji’s air quality.