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Keshan, nestled in the northeastern Heilongjiang province of China, occupies a geographically significant position within the Sanjiang Plain. Located at coordinates 48.0263°N, 125.8659°E, the city’s terrain is largely characterized by flat, alluvial plains formed by the confluence of the Songhua, Nen, and Ussuri rivers – hence the ‘Sanjiang’ designation meaning ‘Three Rivers’. The elevation is relatively low, averaging around 120-150 meters above sea level, contributing to limited natural air dispersion. Keshan’s surrounding landscape is dominated by expansive agricultural lands, primarily dedicated to soybean, corn, and wheat cultivation. This agricultural intensity, while vital to the regional economy, introduces potential sources of particulate matter from soil disturbance and fertilizer use. The city itself is a relatively small urban center, exhibiting a clear urban-rural gradient as it transitions into the surrounding farmland. Historically, the area was sparsely populated, but agricultural development and associated industrial processing (particularly food processing) have driven growth. The proximity to the Russian border also influences regional trade and transport patterns. The flat topography and limited windbreaks exacerbate the potential for pollutant accumulation, making air quality management a crucial concern for this developing city.

Keshan experiences a pronounced continental monsoon climate, heavily influencing its air quality patterns. Winters (November to February) are long, bitterly cold, and dry, often accompanied by temperature inversions. These inversions trap pollutants near the ground, leading to increased concentrations of particulate matter from coal combustion for heating and industrial emissions. February and March often see dust storms originating from the Gobi Desert, further degrading air quality. Spring (April-May) brings a gradual warming trend, but also increased agricultural activity – plowing and fertilizer application – contributing to PM10 levels. Summers (June-August) are relatively warm and wetter, with monsoon influences bringing some cleansing rains, offering periods of improved air quality. However, stagnant air masses can still occur. Autumn (September-October) is generally considered the most pleasant time of year, with clear skies and moderate temperatures, but also sees increased burning of agricultural residue after harvest, impacting air quality. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exertion during winter and periods of agricultural burning. Monitoring wind direction is crucial, as pollutants can be transported from surrounding industrial areas.