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Ayagawa, nestled within Kagawa Prefecture on the island of Shikoku, Japan, presents a unique geographic context influencing its air quality. The city occupies a relatively flat coastal plain, situated at an elevation of approximately 25 meters, bordering the Seto Inland Sea. This proximity to the sea introduces maritime influences, moderating temperatures but also potentially trapping pollutants during stable atmospheric conditions. The surrounding landscape is a mix of agricultural land – Kagawa Prefecture is renowned for its udon wheat and citrus production – and increasingly, suburban development extending from Takamatsu City, the prefectural capital. While Ayagawa itself isn’t heavily industrialised, its position within the broader economic zone of Shikoku means it experiences some regional industrial fallout. The urban-rural gradient is noticeable; moving inland, agricultural areas dominate, offering some natural air filtration. However, the coastal location and prevailing wind patterns can transport pollutants from larger industrial areas further afield. The relatively sheltered nature of the Seto Inland Sea, compared to the open Pacific, can exacerbate pollution episodes, limiting dispersion. Understanding this interplay of coastal geography, agricultural practices, and regional industrial activity is crucial for assessing Ayagawa’s air quality challenges.

Ayagawa’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 are variable, sometimes aiding dispersion, other times creating localised stagnation. Summer (June-August) brings the humid subtropical climate of Shikoku, with the potential for high ozone levels formed under strong sunlight and warm temperatures. The rainy season (Tsuyu) in June-July can temporarily improve air quality by washing away pollutants, but humidity can also trap them. Autumn (September-November) is generally the clearest period, with cooler temperatures, lower humidity, and more consistent winds promoting dispersion. However, temperature inversions can occur, trapping pollutants near the ground. Winter (December-February) presents the most challenging conditions. Cold, dry air from Siberia, combined with weak winds and frequent temperature inversions, leads to the accumulation of pollutants, particularly particulate matter. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during these winter months. Monitoring forecasts and avoiding peak pollution times is advisable year-round, but especially during spring burning and winter stagnation.