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Yunfu is a prefecture-level city in western Guangdong Province, China, situated approximately 130 kilometers west of Guangzhou within the Pearl River Delta economic region. The city occupies a transitional zone between the mountainous terrain of western Guangdong and the alluvial plains of the Pearl River Delta, with an average elevation around 100 meters above sea level. Yunfu's urban core lies along the Nanjiang River, a tributary of the West River, which flows through the city center and influences local humidity patterns. The surrounding landscape features low hills to the north and west, gradually giving way to flatter agricultural lands toward the southeast, creating a distinct urban-rural gradient where industrial zones cluster near transportation corridors while rural areas maintain tea plantations and orchards. This geography creates a semi-enclosed basin effect that can trap pollutants, particularly when combined with the region's high humidity. Yunfu's position within the Pearl River Delta's industrial belt means it receives both locally generated pollution from its manufacturing sectors (notably stone processing, cement production, and metalworking) and regional transport of pollutants from the densely industrialized Guangzhou-Foshan metropolitan area to the east. The city's proximity to the South China Sea (approximately 100 kilometers south) provides some maritime influence, but this is moderated by the intervening terrain. Urban expansion has created heat island effects that interact with the basin topography, occasionally creating conditions conducive to pollution accumulation, especially during periods of atmospheric stability.

Yunfu experiences distinct seasonal air quality patterns shaped by the East Asian monsoon system. During winter (December-February), northeasterly monsoon winds bring drier, cooler air from continental Asia, but temperature inversions frequently develop in the basin topography, trapping pollutants near the surface. This season typically sees the highest pollution concentrations, particularly in January and February when industrial and residential heating emissions combine with stagnant atmospheric conditions. Sensitive groups should limit prolonged outdoor exposure during these months. Spring (March-May) brings transitional weather with increasing humidity and variable winds, leading to moderate pollution levels that gradually improve as monsoon patterns shift. Summer (June-August) features the southwest monsoon from the South China Sea, bringing abundant rainfall and strong southerly winds that effectively disperse pollutants, making this the cleanest season for outdoor activities. However, high temperatures and humidity can exacerbate respiratory discomfort for some individuals. Autumn (September-November) sees a gradual return to stable atmospheric conditions as monsoon winds weaken, with pollution levels slowly rising through October and November as temperature inversions become more frequent. Fog events, particularly in late autumn and winter mornings, can temporarily worsen air quality by trapping moisture and pollutants. The optimal months for outdoor activities are typically June through September, while sensitive groups should exercise particular caution from December through February and monitor local air quality advisories during transitional periods.