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Puli, nestled in the heart of Nantou County, Taiwan, occupies a geographically significant position within the island's central mountain range. Located at approximately 23.9667° N, 120.9667° E and an elevation of around 730 meters (2,400 feet) above sea level, Puli’s terrain is characterized by undulating hills and valleys carved by the Sinwu River and its tributaries. The surrounding landscape is dominated by lush subtropical forests, part of the broader Central Mountain Range ecosystem, providing a natural buffer against some pollutants but also contributing to localized fog formation. Puli sits within a transitional zone, exhibiting a gradual urban–rural gradient. To the west, it connects to the broader Taiwanese plains and agricultural lands, including tea plantations and fruit orchards, which can contribute to volatile organic compound (VOC) emissions. To the east, the terrain rises sharply into the mountains, influencing wind patterns and trapping pollutants under certain meteorological conditions. The city’s proximity to the Sinwu River, while providing a water source, can also be a pathway for pollutants to accumulate. While Puli isn't directly adjacent to major industrial belts, its location within a region experiencing economic development means that transboundary pollution from industrial areas further west and south can occasionally impact air quality. The valley setting, combined with the surrounding mountains, creates a microclimate prone to temperature inversions, particularly during the cooler months, which can exacerbate air pollution episodes by trapping pollutants near the ground. The city’s urban character is a blend of traditional Taiwanese architecture and modern development, with a relatively low population density compared to major coastal cities.

Puli’s air quality exhibits a distinct seasonal pattern dictated by Taiwan’s subtropical climate and prevailing weather systems. The winter months (November to February) are typically the most challenging, characterized by frequent temperature inversions. Cold air settles in the valleys, trapping pollutants released from agricultural burning in surrounding areas and occasional transboundary sources. Fog, a common occurrence during this period, further reduces dispersion, leading to periods of reduced visibility and potentially elevated pollutant concentrations. Spring (March to May) brings warmer temperatures and increased wind speeds, generally improving air quality as inversions become less frequent. However, agricultural activities, including the burning of crop residues, can still contribute to localized pollution spikes. The summer months (June to August) are generally the cleanest, with consistent winds and rainfall helping to disperse pollutants. Monsoon rains play a crucial role in washing away particulate matter. Autumn (September to October) sees a gradual transition, with decreasing rainfall and a return of cooler temperatures, potentially leading to a resurgence of inversions towards the end of the season. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the winter months, limiting outdoor activities during periods of fog or reduced visibility. During agricultural burning seasons, even healthy individuals should consider wearing masks and avoiding prolonged exposure to smoke. The city’s location within a valley means that pollutants can linger longer, so awareness of local weather conditions is key to minimizing exposure.