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Yongcong, nestled within the karst landscape of Guizhou province in southwestern China, presents a unique geographic context for air quality. Located at coordinates 26.0422, 109.1314, the city sits at an elevation of approximately 800 meters, contributing to cooler temperatures and potential for temperature inversions. The surrounding terrain is dominated by rolling hills and limestone formations, typical of the region. While not directly adjacent to a major river, Yongcong is influenced by the hydrological network draining the surrounding mountains. The city’s relatively small population of 13,670 suggests a less intensely urbanized environment compared to China’s megacities, but its position within Guizhou – a province experiencing increasing industrialization – is crucial. Agricultural activity, particularly rice cultivation in the valleys, is prevalent. The urban-rural gradient is relatively sharp, with agricultural lands immediately bordering the city limits. This proximity means potential for agricultural burning impacting local air quality. The valley location, while providing some shelter, can also trap pollutants, especially during periods of calm weather. The regional climate is subtropical, with high humidity and significant rainfall, influencing pollutant dispersion and chemical reactions in the atmosphere. Understanding these geographical factors is vital for assessing and mitigating air pollution in Yongcong.

Yongcong’s air quality follows a distinct seasonal pattern dictated by the subtropical monsoon climate. Spring (March-May) often sees increased dust and pollen levels, exacerbated by agricultural activities preparing fields for planting. Rainfall begins to increase, offering some cleansing, but temperature inversions can still trap pollutants. Summer (June-August) brings the monsoon season, with frequent heavy rainfall effectively washing away many pollutants, resulting in generally better air quality. However, high humidity can promote secondary pollutant formation. Autumn (September-November) is often the most challenging period. Reduced rainfall, combined with cooler temperatures and stable atmospheric conditions, leads to pollutant accumulation. Agricultural burning after the harvest further degrades air quality. This is a period to limit strenuous outdoor activity. Winter (December-February) is relatively dry, with infrequent rainfall and increased reliance on coal for heating in some households, contributing to particulate matter pollution. Fog is common, further reducing visibility and trapping pollutants. Sensitive groups – children, the elderly, and those with respiratory conditions – should take extra precautions during autumn and winter, limiting outdoor exposure and using air purifiers when possible. Months to favour for outdoor activity are generally June through August, during the peak of the monsoon.