Kan’onjichō, nestled within 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, situated at an elevation of approximately 20 meters above sea level, bordering the Seto Inland Sea. This proximity to the sea introduces maritime influences, moderating temperatures and potentially dispersing pollutants, but also contributing to humidity and the formation of sea breezes. The surrounding landscape is a mix of agricultural land – Kagawa Prefecture is renowned for its udon wheat and vegetable production – and low-lying hills. While Kan’onjichō itself isn’t heavily industrialised, its position within the broader Shikoku region means it can be affected by transport of pollutants from industrial areas further afield, particularly those around Takamatsu. The urban-rural gradient is relatively sharp; moving inland quickly transitions from residential and commercial areas to cultivated fields. This proximity to agricultural zones introduces potential sources of ammonia and particulate matter from farming activities. The city’s flat terrain can also contribute to localised pollutant build-up, especially during temperature inversions, trapping emissions near ground level. Understanding these geographical factors is crucial for assessing and mitigating air quality challenges in Kan’onjichō.

Kan’onjichō’s air quality follows a distinct seasonal pattern, largely dictated by meteorological conditions. Spring (March-May) often sees increased particulate matter from agricultural burning and dust storms originating from the Asian continent, carried by prevailing westerly winds. Pollen from local vegetation also contributes to discomfort for allergy sufferers. Summers (June-August) are typically humid, with occasional typhoons bringing heavy rainfall that can temporarily cleanse the air, but also increase mould spore counts. Autumn (September-November) is generally the clearest period, benefiting from cooler temperatures and stable atmospheric conditions. However, temperature inversions become more frequent, trapping pollutants near the ground, particularly in the mornings. Winter (December-February) experiences the lowest wind speeds and frequent temperature inversions, leading to the highest concentrations of pollutants, especially from domestic heating sources. Sensitive groups – the elderly, children, and those with respiratory conditions – should limit strenuous outdoor activity during these winter months. The Seto Inland Sea’s influence moderates temperatures, but also contributes to fog formation, which can exacerbate particulate matter concentrations. Months to favour for outdoor activity are October and November, offering clear skies and moderate temperatures.