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Yecun, a small city nestled within Shaanxi Province, China (coordinates 33.7663° N, 110.1305° E), occupies a position on the North China Plain. The terrain is largely flat, characteristic of the alluvial plains formed by the Wei River, though gentle undulations are present as the land begins to rise towards the Qinling Mountains to the south. This proximity to the mountains influences local weather patterns, creating rain shadows and affecting wind flow. Yecun’s elevation is approximately 380 meters above sea level. The surrounding landscape is a mix of agricultural zones – primarily wheat and maize cultivation – and increasingly, light industrial activity associated with the broader urban agglomeration of Weinan, to which Yecun is closely linked. The urban-rural gradient is sharp, transitioning quickly from denser residential areas to farmland. This proximity to agricultural land contributes to seasonal biomass burning, a source of particulate matter. The Wei River, while vital for irrigation, can also act as a conduit for pollutants from upstream sources. The city’s location within a basin can exacerbate pollution episodes due to limited atmospheric dispersion, trapping emissions during periods of calm weather. The prevailing winds are generally from the north and west, carrying pollutants from regional industrial centres.

Yecun experiences a distinct temperate monsoon climate, heavily influencing its air quality. Spring (March-May) sees increasing dust storms originating from the Gobi Desert, raising PM10 levels. Agricultural burning after the winter harvest also contributes to particulate matter. Summer (June-August) brings the monsoon season, offering periods of cleaner air due to rainfall washing pollutants from the atmosphere and increased wind speeds. However, high humidity can also foster secondary pollutant formation. Autumn (September-November) is often the most polluted period. Reduced rainfall, temperature inversions, and increased coal combustion for heating create stagnant air conditions, trapping pollutants. November is particularly concerning. Winter (December-February) continues the trend of poor air quality, with persistent temperature inversions and reliance on coal for heating. Fog is common, exacerbating particulate matter concentrations. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during autumn and winter. Spring dust storms also necessitate caution. Monitoring wind direction is crucial; winds from the north and west typically indicate poorer air quality. Avoiding strenuous activity during peak pollution periods is advised.