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Zaojiao, nestled within Gansu Province in northwestern China, occupies a geographically complex position at coordinates 34.4727°N, 105.7062°E. The city’s terrain is characterised by the foothills of the Qinling Mountains, transitioning into the Loess Plateau, creating a landscape of undulating hills and fertile, yet erosion-prone, soil. With an elevation around 1600 meters, Zaojiao experiences a continental climate, marked by significant temperature variations. The city is not directly adjacent to major bodies of water, though the Wei River flows relatively nearby, influencing local humidity patterns. Zaojiao’s regional position places it within a developing industrial corridor, with agricultural zones dominating the surrounding rural areas, primarily focused on wheat and corn cultivation. This mix of industry and agriculture contributes to specific pollution sources. The urban-rural gradient is relatively sharp, with a rapid transition from denser residential areas to agricultural land. This proximity to agricultural practices, including the use of fertilizers and potential burning of crop residue, impacts local air quality. The surrounding Loess Plateau is prone to dust storms, particularly during drier periods, exacerbating particulate matter concentrations. The city’s location within a valley can also trap pollutants, limiting dispersion.

Zaojiao’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees increased dust and particulate matter due to wind erosion from the Loess Plateau and agricultural burning, making outdoor activity less favourable. Summers (June-August) bring monsoon influences, offering periods of cleaner air with rainfall washing away pollutants, though humidity can contribute to secondary pollutant formation. However, increased energy demand for cooling can elevate emissions. Autumn (September-November) is typically the most pleasant period for air quality, with stable atmospheric conditions and reduced agricultural activity. However, heating demand begins to rise towards November, potentially increasing coal combustion. Winters (December-February) are the most challenging. Cold temperatures lead to increased coal use for heating, creating temperature inversions that trap pollutants close to the ground. These inversions, combined with low wind speeds, result in prolonged periods of poor air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exposure during winter months. Fog is also common, exacerbating particulate matter concentrations. Months to avoid for strenuous outdoor activity are generally December through February, while June and September offer the best conditions.