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Ino, a city nestled within Kōchi Prefecture on the island of Shikoku, Japan, presents a unique geographic context influencing its air quality. Located at 33.5500°N, 133.4333°E, the city occupies a relatively low-lying area, though surrounded by the rolling hills characteristic of Shikoku’s interior. The Niyodo River, a vital waterway known for its exceptionally clear water, flows nearby, providing a natural element but also potentially trapping pollutants during temperature inversions. Ino’s urban character is defined by a blend of residential areas and smaller-scale commercial activity, reflecting its population of approximately 20,750. Unlike the heavily industrialized zones of Honshu, Kōchi Prefecture maintains a stronger agricultural base, with rice paddies and forestry dominating the surrounding landscape. This agricultural presence contributes to seasonal biomass burning, a potential source of particulate matter. The urban-rural gradient is relatively sharp, transitioning quickly to forested slopes. Proximity to the coast, while not directly on the shoreline, means the city is susceptible to maritime air masses, which can either dilute or concentrate pollutants depending on prevailing winds. The terrain funnels winds through valleys, creating localized areas of higher and lower ventilation. This complex interplay of topography and land use significantly shapes Ino’s air quality profile.

Ino’s air quality follows a distinct seasonal pattern, heavily influenced by the region’s subtropical climate. Spring (March-May) often sees increased pollen counts, impacting respiratory health, alongside potential agricultural burning as fields are prepared. Summer (June-August) brings the humid monsoon season, with frequent rainfall generally cleansing the air, though high humidity can exacerbate the effects of existing pollutants. However, stagnant air during breaks in the monsoon can lead to localized build-up. Autumn (September-November) is typically the clearest period, with stable high-pressure systems bringing dry, well-ventilated conditions. This is the most favourable time for outdoor activities. Winter (December-February) presents the greatest challenges. Temperature inversions, common in valleys, trap cold air near the ground, concentrating pollutants from residential heating and limited industrial activity. Dry conditions and northerly winds can also carry pollutants from other parts of Japan. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during winter mornings. Fog, prevalent in winter, further reduces air quality. Monitoring wind direction is crucial; southerly breezes generally improve conditions, while northerly winds can worsen them.