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Guoxing, nestled within Nantou County in central Taiwan, occupies a geographically significant position within the island’s mountainous interior. Located at approximately 24.0550° N, 120.8700° E, and at an elevation of around 850 meters (2,789 feet) above sea level, the town is characterized by steep, forested slopes and a relatively narrow valley floor. The surrounding landscape is dominated by the Central Mountain Range, a major geological feature influencing regional weather patterns and air circulation. Guoxing’s proximity to the Sun Moon Lake, Taiwan’s largest lake, plays a crucial role in local microclimates, often moderating temperatures and contributing to humidity. The urban character of Guoxing is distinctly rural, with a small population of 17,168, primarily engaged in agriculture and tourism. The surrounding area is a patchwork of tea plantations, fruit orchards, and traditional farming communities, creating a clear urban–rural gradient. While Guoxing itself lacks significant heavy industry, it benefits from its location within a broader agricultural belt and is within reasonable distance of industrial zones concentrated along the western coast of Taiwan. This proximity can occasionally lead to the transport of pollutants from those areas, particularly during periods of stagnant air. The terrain, with its steep slopes and limited valley openings, can trap pollutants, especially when coupled with temperature inversions, a common occurrence during the cooler months. The valley’s orientation also influences prevailing wind patterns, impacting the dispersion of airborne particles.

Guoxing’s air quality experiences a distinct seasonal cycle heavily influenced by Taiwan’s subtropical climate and monsoon patterns. The winter months (November to February) typically see the poorest air quality. Cold, stable air masses frequently settle into the valley, creating temperature inversions where a layer of warm air traps cooler air and pollutants near the ground. This phenomenon, combined with reduced wind speeds and increased humidity from the lake, leads to a build-up of particulate matter. Fog is also common during this period, further exacerbating the issue by trapping pollutants. Spring (March to May) brings a gradual improvement as temperatures rise and winds increase, dispersing pollutants more effectively. The arrival of the northeast monsoon gradually weakens, allowing for better ventilation. Summer (June to August) generally offers the best air quality, with frequent rainfall washing away pollutants and strong winds dispersing any accumulated particles. However, occasional typhoons can briefly disrupt this pattern. Autumn (September to October) marks a transitional period, with decreasing rainfall and a return to more stable atmospheric conditions. As temperatures cool, the risk of temperature inversions increases, and air quality can begin to deteriorate towards the end of the season. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the winter months, limiting outdoor activities during periods of stagnant air and fog. Staying informed about local weather forecasts and air quality reports is crucial for making informed decisions about outdoor exposure throughout the year.