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Caotan, nestled within Gansu province in northwestern China, occupies a geographically significant position within the Hexi Corridor, a historical trade route connecting eastern and western China. Located at approximately 36.27°N, 105.20°E and an elevation of around 1,450 meters (4,757 feet) above sea level, the city’s terrain is characterized by a semi-arid landscape dominated by loess plateaus and undulating hills. The surrounding region is largely rural, comprising agricultural lands primarily dedicated to wheat and corn cultivation, interspersed with sparse grasslands. To the south, the Qilian Mountains rise dramatically, influencing local weather patterns and contributing to occasional dust events. Caotan’s proximity to the Gobi Desert, though not immediately adjacent, means it is susceptible to long-range transport of dust and sand, particularly during spring and summer. The city’s urban character is relatively small-scale, reflecting its modest population of 11,294. While industrial activity is present, it’s less pronounced than in larger urban centers within Gansu. The urban–rural gradient is gradual, with agricultural fields and scattered settlements extending outwards from the city limits. This combination of semi-arid climate, proximity to desert regions, and the influence of the Qilian Mountains creates a unique environmental setting that significantly impacts air quality, making it vulnerable to both local and regional pollution sources. The lack of significant surface water bodies further exacerbates the dryness, contributing to particulate matter suspension.

Caotan’s air quality follows a distinct seasonal pattern dictated by its climate and regional weather systems. Winters (November – February) are typically the most challenging, characterized by frequent temperature inversions trapping pollutants close to the ground. Cold, stable air masses settle in the Hexi Corridor, hindering vertical mixing and allowing emissions from local sources and long-range transport to accumulate. Dust storms, though less frequent than in more desert-exposed areas, can still occur. Spring (March – May) brings increased dust activity as the Gobi Desert experiences stronger winds, leading to elevated particulate matter levels. Agricultural activities, including tilling and fertilizer application, also contribute to localized pollution. Summer (June – August) generally sees improved air quality due to increased rainfall and stronger winds that disperse pollutants. However, occasional heatwaves can lead to stagnant air conditions. Autumn (September – October) offers the most consistently favorable air quality, with moderate temperatures and wind patterns that promote ventilation. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter and spring months, limiting outdoor exposure and wearing appropriate masks when necessary. During periods of high dust, staying indoors with windows closed is advisable. The monsoon season, though less pronounced than in southern China, still plays a role in summer, bringing occasional rainfall that helps to cleanse the atmosphere. Fog, common during the colder months, further exacerbates pollution by trapping particles.