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Baiceng, nestled within the mountainous province of Guizhou in southwestern China, presents a unique geographic challenge for air quality. Located at coordinates 25.4333°N, 105.8000°E, the city sits at a considerable elevation, typical of the karst topography that dominates this region. This terrain, characterised by limestone formations and deep valleys, restricts air circulation, fostering localized pollution build-up. The surrounding landscape is predominantly rural, a mosaic of agricultural lands – primarily rice and corn – and forested hills. While Baiceng itself is a small city with a population of approximately 15,464, its proximity to larger industrial centres within Guizhou province, particularly those involved in mining and manufacturing, contributes to regional background pollution. The Hongshui River flows nearby, but its influence on local air quality is limited by the valley’s topography. The urban-rural gradient is steep; the city centre quickly transitions to agricultural fields and then dense forest. This limited urban sprawl means emissions are concentrated, but dispersion is hampered by the surrounding hills. The prevailing winds, often influenced by the complex terrain, play a crucial role in either trapping or flushing out pollutants. The valley location creates a bowl-like effect, exacerbating the potential for temperature inversions, which further impede vertical mixing of air.

Baiceng’s air quality follows a distinct seasonal pattern dictated by Guizhou’s subtropical monsoon climate. The dry season, spanning roughly November to February, often sees the poorest air quality. Reduced rainfall means less atmospheric cleansing, and increased reliance on coal for heating exacerbates particulate matter pollution. Temperature inversions are common during these colder months, trapping pollutants in the valley. Spring (March-May) brings increased rainfall and gradually improving conditions, though dust from agricultural activities can temporarily elevate PM10 levels. Summer (June-August) is typically the cleanest period, with the monsoon rains effectively washing away pollutants and high humidity suppressing dust. However, intense localised thunderstorms can stir up existing particulate matter. Autumn (September-October) sees a transition period; rainfall decreases, and agricultural burning becomes more prevalent, leading to a rise in PM2.5. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the dry season and periods of agricultural burning. Fog is frequent, particularly in winter, and can trap pollutants at ground level. Months to avoid for outdoor activity are December and January; May and June are generally favourable.