Toucheng, nestled in the Yilan County of Taiwan, presents a unique geographic setting influencing its air quality. Situated at coordinates 24.8500, 121.8167, the city lies on the northern coastal plain, bordering the Pacific Ocean. The terrain is relatively flat, transitioning to the steeper slopes of the Xue Shan mountain range to the south and west. This proximity to both the ocean and mountains creates complex meteorological patterns. Toucheng’s urban character is a blend of residential areas, small-scale commercial activity, and agricultural land, particularly rice paddies and fruit orchards. The surrounding landscape is dominated by lush greenery, typical of Taiwan’s eastern coast. While Yilan County is generally less industrialised than western Taiwan, regional industrial activity in nearby cities can contribute to transboundary pollution. The urban-rural gradient is noticeable, with air quality generally improving as one moves away from the town centre and towards the coastal areas or foothills. The prevailing winds, often influenced by the East Asian Monsoon, play a crucial role in dispersing or concentrating pollutants. The coastal location also means potential for sea breezes to impact local air circulation and pollutant transport. This interplay of factors makes Toucheng’s air quality dynamic and sensitive to regional and seasonal changes.

Toucheng’s air quality follows a distinct seasonal pattern, largely dictated by Taiwan’s subtropical monsoon climate. Spring (March-May) often sees increased particulate matter from agricultural burning and dust storms originating from mainland China, carried by prevailing winds. Rainfall increases during this period, offering some natural cleansing, but humidity can also trap pollutants. Summer (June-August) brings the southwest monsoon, generally improving air quality through increased wind speeds and rainfall, washing away accumulated pollutants. However, high temperatures can contribute to ozone formation. Autumn (September-November) is often the clearest period, with stable atmospheric conditions and reduced rainfall. This is the most favourable time for outdoor activities. Winter (December-February) presents the most challenging conditions. The northeast monsoon brings cold, dry air masses, often leading to temperature inversions. These inversions trap pollutants near the ground, resulting in poorer air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during prolonged inversion events. Fog is also common in winter, exacerbating particulate matter concentrations. Monitoring wind direction and avoiding activity during stagnant air periods is crucial for health protection.