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Lunbei, nestled in Yunlin County, southwestern Taiwan (23.7789° N, 120.3331° E), occupies a geographically significant position within the island’s agricultural heartland. The city’s terrain is predominantly flat, characteristic of the coastal plains that define much of Yunlin. Its elevation is relatively low, averaging around 15 meters above sea level, contributing to a susceptibility to coastal influences and potential for ground-level ozone formation during warmer months. Lunbei sits within the Changhua-Yunlin Plain, a fertile region heavily reliant on agriculture, particularly rice cultivation and aquaculture. This agricultural activity, while vital to the local economy, introduces localized sources of ammonia and particulate matter, impacting air quality. The surrounding landscape is a patchwork of rice paddies, fruit orchards (especially pomelos and mangoes), and aquaculture ponds, creating a distinct urban–rural gradient. To the east, the terrain gradually rises towards the foothills of the Central Mountain Range, though Lunbei itself remains far removed from significant orographic effects. The proximity to the Taiwan Strait exposes the city to maritime influences, including sea breezes that can disperse pollutants, but also introduce salt spray and, occasionally, transboundary pollutants from mainland China. The region’s industrial presence is relatively limited compared to northern Taiwan, but nearby industrial belts in Taichung and Chiayi can contribute to regional pollution episodes, particularly during periods of stagnant air. The flat topography and prevailing wind patterns often lead to pollutant accumulation, especially during temperature inversions.

Lunbei’s air quality exhibits a distinct seasonal pattern dictated by Taiwan’s subtropical climate. The warmer, drier months (April to September) generally see a rise in air pollution, primarily due to increased photochemical smog formation. High temperatures and abundant sunshine fuel the production of ground-level ozone, exacerbated by emissions from agricultural activities and occasional transport of pollutants from industrial areas. June to August are typically the most challenging months, with stagnant air masses frequently trapping pollutants near the surface. The northeast monsoon season (October to March) brings cooler temperatures and increased rainfall, which naturally helps to cleanse the atmosphere, leading to improved air quality. However, periods of weak or absent monsoon winds can still result in localized pollution episodes, particularly when combined with fog or temperature inversions. During the winter months, fog events, common in Yunlin County, can trap pollutants, leading to reduced visibility and elevated concentrations of particulate matter. Spring (March-April) sees a gradual transition, with improving air quality as rainfall decreases and temperatures rise. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the warmer months, limiting outdoor activities during peak ozone hours (typically midday to early evening). The agricultural burning season, though regulated, can also contribute to particulate matter spikes, particularly in the autumn months. Maintaining awareness of local weather forecasts and air quality reports is crucial for informed decision-making regarding outdoor exposure.