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Guotang, nestled within Guangdong Province, China, occupies a geographically significant position within the Pearl River Delta, a region renowned for its rapid urbanization and industrial development. Located at approximately 23.8384° N, 115.9201° E, the city’s terrain is characterized by gently rolling hills transitioning into a low-lying coastal plain. This topography influences local air circulation patterns, often trapping pollutants in valleys during periods of low wind. Guotang’s proximity to the Pearl River, a vital waterway for transportation and industry, contributes to both its economic vitality and potential air quality challenges. The surrounding landscape is a mosaic of agricultural land – primarily rice paddies and fruit orchards – interspersed with burgeoning industrial zones and expanding urban sprawl. The urban–rural gradient is relatively sharp, with the city’s core exhibiting dense construction and heavy traffic, gradually giving way to more rural agricultural settings within a short distance. Guotang’s location within the broader industrial belt of the Pearl River Delta means it is susceptible to transboundary pollution, with emissions from neighboring cities impacting local air quality. The prevailing southeasterly winds, common throughout much of the year, can carry pollutants from upwind industrial areas. Elevation is relatively low, averaging around 20-40 meters above sea level, which limits vertical dispersion of pollutants and exacerbates ground-level concentrations. The region's subtropical climate, with its distinct wet and dry seasons, further complicates air quality management, influencing both emission sources and atmospheric conditions.

Guotang’s air quality experiences a pronounced seasonal cycle dictated by its subtropical monsoon climate. The dry season, typically spanning from October to April, often witnesses the most challenging air quality conditions. Reduced rainfall and lower humidity contribute to the accumulation of particulate matter and other pollutants. Temperature inversions, common during these months, trap emissions close to the ground, intensifying localized pollution. November and December frequently see periods of stagnant air, exacerbated by the influence of Siberian High pressure systems. Conversely, the wet season, from May to September, brings relief through frequent rainfall, which naturally scrubs the atmosphere. However, heavy rainfall can also lead to increased runoff carrying pollutants into waterways, indirectly impacting air quality. The summer monsoon brings increased humidity, which can sometimes trap pollutants, but generally promotes better dispersion. Fog, particularly prevalent during the late autumn and winter months, significantly reduces visibility and concentrates pollutants. During the spring (March-April), agricultural burning, a traditional practice, can contribute to elevated particulate matter levels. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of stagnant air or fog. Outdoor activities are generally more favorable during the wet season, although monitoring local conditions remains crucial. The transition months of May and October can be unpredictable, with periods of both improved and degraded air quality.