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Yizhu, nestled within Chiayi County in southwestern Taiwan (23.3565° N, 120.2235° E), occupies a geographically complex and subtly influential position. The township sits at an elevation of approximately 150 meters above sea level, transitioning from the coastal plains towards the foothills of the Central Mountain Range. This location creates a unique microclimate and impacts air quality dynamics. Yizhu is surrounded by a mosaic of agricultural land, primarily dedicated to fruit orchards (particularly pomelos and mangoes) and rice paddies, contributing to both rural charm and potential biogenic volatile organic compound (BVOC) emissions. To the west lies the Taiwan Strait, offering a degree of maritime influence, though prevailing winds often originate from the east. The township’s urban character is distinctly rural, with a dispersed settlement pattern rather than a concentrated urban core. While Chiayi City, a larger urban center, lies approximately 20 kilometers to the northeast, Yizhu’s relative isolation mitigates direct exposure to its industrial emissions. However, regional industrial belts concentrated further north along the western coast can still contribute to transboundary pollution events. The urban-rural gradient is gradual, with agricultural fields seamlessly blending into residential areas. Topographically, the gently sloping terrain can occasionally trap pollutants, particularly during periods of low wind speed and stable atmospheric conditions, exacerbating localized air quality challenges. The surrounding landscape, characterized by rolling hills and verdant agricultural fields, contributes to the overall aesthetic but also influences the dispersion of airborne pollutants.

Yizhu’s air quality experiences a distinct seasonal pattern dictated by Taiwan’s subtropical climate and monsoon influences. The warmer, wetter months (May to September) generally see improved air quality due to increased rainfall, which naturally scrubs pollutants from the atmosphere, and more frequent convective mixing, which disperses them. However, agricultural burning, a traditional practice for land clearing and crop residue disposal, can significantly elevate particulate matter concentrations during these months, particularly in late summer. The cooler, drier months (October to April) present a greater air quality challenge. Temperature inversions, common during this period, trap pollutants near the ground, leading to stagnant air and increased concentrations of fine particulate matter. November and December often experience the most persistent inversions, coinciding with the northeast monsoon season, which brings cooler, drier air from the Chinese mainland. Fog, frequently occurring during the winter months, further exacerbates this issue by reducing visibility and trapping pollutants. Spring (March-April) sees a gradual improvement as temperatures rise and winds increase. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the cooler, drier months, particularly during periods of fog or temperature inversions. Outdoor activities are generally more favorable during the wetter months, although agricultural burning events should be monitored. The transition months of May and October can be unpredictable, with periods of both good and poor air quality depending on weather patterns.