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Shetang, a small city nestled within Gansu Province in northwestern China, occupies a geographically complex position along the Loess Plateau. Located at coordinates 34.5514° N, 105.9703° E, the city’s elevation contributes to its distinct climate and air quality challenges. The surrounding landscape is dominated by undulating loess hills, a characteristic feature of the region, formed by centuries of wind-blown sediment from the Gobi Desert. This terrain significantly influences air circulation, often trapping pollutants in localized pockets. Shetang isn’t directly adjacent to a major body of water, but lies within the Wei River basin, benefiting from, and potentially impacting, its water resources. The urban-rural gradient is sharp; Shetang is a relatively small settlement surrounded by extensive agricultural lands, primarily wheat and corn cultivation. While not a major industrial hub itself, Shetang’s proximity to larger industrial centres further east, particularly those involved in petrochemicals and heavy manufacturing, means it can experience transboundary pollution. Dust storms originating from the Gobi Desert are a frequent occurrence, exacerbating particulate matter concentrations. The loess soil itself is easily eroded, contributing to local dust levels, especially during drier periods. This combination of factors creates a unique set of air quality conditions for Shetang.

Shetang experiences a pronounced continental climate, heavily influencing its air quality throughout the year. Spring (March-May) sees a surge in dust storms originating from the Gobi Desert, dramatically increasing particulate matter (PM10 and PM2.5) levels. These storms, coupled with agricultural burning as farmers prepare fields, create particularly challenging conditions. Summers (June-August) are relatively cleaner, with occasional rainfall helping to suppress dust, but temperatures can rise significantly, promoting ozone formation. Autumn (September-November) often presents a period of worsening air quality as heating demand begins, and stagnant air masses become more frequent, trapping pollutants from local sources and regional transport. Temperature inversions are common during this season, exacerbating pollution build-up. Winter (December-February) is typically the most polluted period. Coal combustion for heating is widespread, releasing significant amounts of sulfur dioxide, nitrogen oxides, and particulate matter. Low wind speeds and persistent temperature inversions further concentrate these pollutants. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during spring and winter. Months to favour for outdoor activity are July and August, though ozone levels should still be monitored.