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Dacheng Township, nestled within Changhua County in western Taiwan, presents a unique geographic setting influencing its air quality. Situated at coordinates 23.8483°N, 120.3089°E, the township occupies a relatively low-lying area of the Changhua Plain, a fertile expanse formed by alluvial deposits from several rivers. The terrain is predominantly flat, gradually rising towards the foothills of the Bagua Plateau to the east. This flatness contributes to potential air stagnation. Dacheng is approximately 8km inland from the Taiwan Strait, meaning coastal breezes offer some, but limited, dispersion. The surrounding landscape is a mosaic of intensely cultivated agricultural land – primarily rice paddies and fruit orchards – interspersed with pockets of light industrial activity, particularly related to food processing and small-scale manufacturing. The urban-rural gradient is quite sharp; Dacheng itself is a smaller township, with denser settlement concentrated around the main transport routes, quickly giving way to agricultural fields. This proximity to both agricultural practices (potential ammonia emissions from fertilizers) and industry, combined with the flat topography and occasional temperature inversions common in Taiwan’s plains, creates conditions that can trap pollutants. The regional climate is subtropical, with high humidity and distinct wet and dry seasons, further impacting pollutant dispersion.

Dacheng’s air quality follows a distinct seasonal pattern dictated by Taiwan’s subtropical monsoon climate. The winter months (November to March) typically experience the poorest air quality. This is due to the prevailing northeast monsoon winds bringing pollutants from industrial areas further north, coupled with increased temperature inversions which trap air close to the ground. Rainfall is lower during this period, reducing the natural cleansing effect of precipitation. Outdoor activity should be minimized during prolonged periods of stagnant air, particularly for individuals with respiratory conditions. Spring (April-May) sees a gradual improvement as the monsoon shifts and rainfall increases, washing away accumulated pollutants. Summer (June-August) generally offers the cleanest air, with frequent heavy rainfall and stronger southerly winds dispersing pollutants. However, high temperatures can contribute to ozone formation. Autumn (September-October) is a transitional period, with decreasing rainfall and a return to more stable atmospheric conditions, leading to a gradual decline in air quality. Typhoons, common during late summer and autumn, can temporarily improve air quality through strong winds and heavy rain, but also disrupt infrastructure and potentially release pollutants from damaged facilities. Sensitive groups should monitor conditions closely during these events.