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Higashimiyoshi, nestled within Tokushima Prefecture on Shikoku Island, Japan, presents a unique geographic setting influencing its air quality. The city occupies a basin-like terrain, cradled by the Yoshino River and surrounding mountains, with coordinates placing it at 34.0333°N, 133.9333°E. This inland location, approximately 20km from the coast, shields it somewhat from direct marine influences but also contributes to potential air stagnation. The elevation varies considerably within the city limits, rising towards the forested hills that define its boundaries. Surrounding Higashimiyoshi are predominantly agricultural lands, particularly citrus orchards and rice paddies, with pockets of smaller-scale industry focused on food processing and light manufacturing. The urban-rural gradient is quite sharp; the city centre is relatively compact, quickly transitioning to rural landscapes. This proximity to agricultural activities introduces potential sources of ammonia and particulate matter from fertilizer use and biomass burning. The basin topography, combined with prevailing wind patterns, can trap pollutants during periods of low wind speed, exacerbating local air quality issues. The Yoshino River, while a vital resource, can also contribute to humidity and potentially influence the dispersion of pollutants. Understanding this interplay of terrain, land use, and climate is crucial for assessing and mitigating air pollution in Higashimiyoshi.

Higashimiyoshi’s air quality follows a distinct seasonal pattern dictated by meteorological conditions and human activity. 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 generally moderate, aiding some dispersion. Summer (June-August) brings the humid subtropical climate of Tokushima Prefecture into full force, with the rainy season initially improving air quality through wet deposition. However, stagnant air masses can develop during periods of intense heat, trapping pollutants. Autumn (September-November) is typically the clearest period, with cooler temperatures, increased wind speeds, and reduced agricultural activity. This is the most favourable time for outdoor activities. Winter (December-February) presents the most challenging conditions. Temperature inversions are common in the basin, trapping cold air and pollutants near the ground. Reduced sunlight hours limit photochemical reactions that break down pollutants. Sensitive individuals, including those with respiratory conditions and the elderly, should limit strenuous outdoor activity during these winter months. Fog formation, common in the basin, can further exacerbate particulate matter concentrations. Monitoring wind direction is key, as pollutants can accumulate when winds are light and from the north or west.