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Hejiaji, a small city nestled within Shaanxi Province, China, occupies a geographically significant position in the Loess Plateau region. Located at coordinates 37.3569°N, 109.8514°E, the city’s terrain is characterized by undulating hills and fertile plains formed by centuries of loess deposition. This landscape, while agriculturally productive, contributes to dust storms, particularly during drier periods. Hejiaji’s elevation, approximately 1100 meters above sea level, influences temperature patterns and atmospheric circulation. The city isn’t directly adjacent to major bodies of water, but benefits from irrigation sourced from the Yellow River, which flows nearby. Surrounding Hejiaji are extensive agricultural zones, primarily focused on wheat and maize cultivation, alongside smaller-scale industrial activity related to agricultural processing and local manufacturing. The urban-rural gradient is quite sharp; the city centre is densely populated, quickly transitioning to farmland and sparsely populated hills. This proximity to agricultural land means potential for seasonal burning of crop residue, impacting local air quality. The prevailing winds, often originating from the northwest, carry dust and pollutants from the Gobi Desert and industrial areas further east, exacerbating air quality challenges. The Loess Plateau’s inherent erodibility further compounds these issues, making Hejiaji particularly vulnerable to particulate matter pollution.

Hejiaji experiences a distinct seasonal air quality pattern dictated by its continental monsoon climate. Spring (March-May) sees a surge in pollution due to dust storms originating from the Gobi Desert, coupled with increased agricultural burning as farmers prepare fields. Winds are strong and frequent, transporting particulate matter across the region. Summer (June-August) brings the monsoon season, offering temporary relief through rainfall which washes pollutants from the air. However, high humidity can also trap pollutants near the ground. Autumn (September-November) is often the most challenging period. Temperatures drop, leading to temperature inversions – a stable layer of warm air trapping cooler, polluted air below. Reduced wind speeds further exacerbate the situation, and coal burning for heating begins to increase. Winter (December-February) is cold and dry, with frequent temperature inversions and increased reliance on coal for heating, resulting in consistently poor air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during spring and autumn, and consider using air purifiers indoors. Avoid strenuous activity outdoors during periods of stagnant air, and monitor local conditions closely. The months of July and August generally offer the best air quality, though humidity can be high.