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Hengkou, nestled within Shaanxi Province in central China, occupies a geographically complex position. Located at coordinates 32.7378, 108.7695, the city sits on the eastern edge of the Loess Plateau, a vast, sediment-rich highland sculpted by the Yellow River. The terrain is undulating, characterised by eroded gullies and terraces, influencing local wind patterns and pollutant dispersion. Hengkou’s elevation, approximately 850 meters above sea level, contributes to cooler temperatures and potential for temperature inversions, trapping pollutants near the ground. The city is not directly adjacent to a major body of water, but is influenced by the climate patterns originating from the Yellow River basin. Surrounding Hengkou are significant agricultural zones, primarily wheat and maize cultivation, alongside smaller-scale industrial activity focused on processing agricultural products and light manufacturing. The urban-rural gradient is relatively sharp; the city centre is densely populated, while the periphery quickly transitions into farmland and loess hills. This proximity to agricultural land introduces potential sources of particulate matter from dust and seasonal burning of crop residue. The Loess Plateau’s inherent susceptibility to wind erosion further exacerbates particulate matter concentrations, impacting Hengkou’s overall air quality profile. The city’s position within a regional network of transportation routes also contributes to emissions from vehicle traffic.

Hengkou experiences a distinct temperate monsoon climate, profoundly influencing its air quality throughout the year. Spring (March-May) often sees increased dust storms originating from the Gobi Desert and the Loess Plateau itself, elevating particulate matter levels. Agricultural burning following the winter harvest also contributes to localised pollution spikes. Summers (June-August) bring the East Asian monsoon, offering periods of cleaner air due to increased rainfall and wind dispersal, though high temperatures can promote ozone formation. However, humidity can also lead to stagnant air conditions. Autumn (September-November) is generally considered the most pleasant time for air quality, with cooler temperatures and reduced agricultural activity. However, coal combustion for heating begins to increase as temperatures drop, leading to a gradual deterioration in air quality. Winter (December-February) is the most challenging period. Cold temperatures and frequent temperature inversions trap pollutants, particularly from coal burning for residential and industrial heating. Fog is also common, further reducing visibility and exacerbating pollution. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor activity during winter and spring. Monitoring wind direction is crucial; winds from the northwest often carry dust and pollutants from upwind sources. Avoiding peak heating hours can also reduce exposure.