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Fangyuan, nestled in Changhua County, Taiwan (23.9250° N, 120.3158° E), occupies a geographically significant position within the island’s western coastal plain. The city’s terrain is predominantly flat, characteristic of the alluvial plains formed by the Changhua River and its tributaries. This low elevation, averaging around 15 meters above sea level, contributes to a unique atmospheric profile susceptible to pollutant accumulation. Fangyuan’s location is crucial; it lies within a region heavily influenced by agricultural activity, particularly rice cultivation and aquaculture, which can contribute to localized emissions of ammonia and particulate matter. To the east, gently rolling hills mark the transition to more rugged terrain, influencing prevailing wind patterns. The proximity to the Taiwan Strait exposes Fangyuan to maritime influences, including sea breezes that can disperse pollutants, but also introduce salt aerosols. The urban–rural gradient is relatively gradual, with agricultural lands intermingling with residential areas, creating a complex interplay between rural and urban pollution sources. Furthermore, Fangyuan’s position within the broader western corridor of Taiwan places it within a zone experiencing significant industrial activity, particularly in nearby Taichung and Yunlin, which can lead to transboundary pollution events. The flat topography limits natural ventilation, and the surrounding landscape, while largely agricultural, doesn't offer significant topographical barriers to pollutant transport, making air quality management a key consideration for the city’s sustainable development.

Fangyuan’s air quality exhibits a distinct seasonal pattern dictated by Taiwan’s subtropical climate and monsoon influences. The winter months (November to February) typically see the poorest air quality. A dominant feature is the prevalence of temperature inversions, where a layer of warm air traps cooler air near the ground, preventing vertical mixing and leading to pollutant accumulation. Northerly winds, associated with the northeast monsoon, frequently bring pollutants from industrial areas further north and inland. Fog, common during these colder months, exacerbates the problem by trapping particulate matter close to the ground. Spring (March to May) brings a gradual improvement as temperatures rise and wind speeds increase, dispersing pollutants. The southwest monsoon begins to assert itself, bringing cleaner air from the ocean. Summer (June to August) generally offers the best air quality, with frequent sea breezes and rainfall helping to flush out pollutants. However, periods of stagnant weather can still lead to localized pollution episodes. Autumn (September to October) sees a transitional period, with decreasing rainfall and increasing northerly winds, potentially leading to a gradual decline in air quality as winter approaches. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the winter months, limiting outdoor activity on days with visible haze or reduced visibility. Maintaining indoor air quality through proper ventilation and air purification is also recommended during these periods.