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Dalian occupies a strategic position on the Liaodong Peninsula in Northeast China, where the Yellow Sea meets the Bohai Sea, creating a unique coastal geography that profoundly influences its air quality. The city's urban character blends modern port infrastructure with hilly terrain, as it sprawls across numerous bays and peninsulas at elevations ranging from sea level to over 600 meters in the surrounding hills. This topography creates natural ventilation corridors but also traps pollutants in certain valleys. Dalian's location within the Bohai Rim Economic Circle places it at the heart of one of China's most industrialized regions, with heavy manufacturing, petrochemical complexes, and shipping activities concentrated along its coastline and in nearby cities like Anshan and Shenyang. The urban-rural gradient shows dense development along the coast transitioning to agricultural zones inland, where crop burning occasionally contributes to regional haze. Proximity to the sea moderates temperatures but also brings marine aerosols and occasional sea fog that can mix with urban emissions. During winter, cold air from the Siberian High sweeps across the relatively flat North China Plain, carrying industrial pollutants from inland cities toward Dalian's coastal location, where they sometimes accumulate under stable atmospheric conditions. The city's position as a major port means constant ship traffic adds to the local pollution burden, particularly sulfur dioxide and particulate matter from marine fuels.

Dalian's air quality follows a distinct seasonal rhythm shaped by its coastal climate and regional pollution patterns. Winter (December-February) typically brings the worst air quality as cold, stable air from the Siberian High settles over Northeast China, creating frequent temperature inversions that trap pollutants from local heating sources and industrial activities across the Bohai Rim. These months see increased coal burning for heating and persistent northwesterly winds that transport industrial emissions from inland cities toward the coast. Sensitive groups should limit prolonged outdoor exposure during winter stagnation events. Spring (March-May) offers gradual improvement as increasing solar radiation breaks up inversions and southerly winds begin to prevail, though dust storms from the Gobi Desert can occasionally degrade air quality in March and April. Summer (June-August) provides the cleanest air with the East Asian monsoon bringing frequent precipitation that scrubs pollutants from the atmosphere, while sea breezes provide natural ventilation—ideal months for outdoor activities. Autumn (September-November) begins with relatively good conditions but sees gradual deterioration as heating season approaches and atmospheric stability increases, with October often marking a transition toward winter pollution patterns. Throughout the year, sea fog is most common in spring and summer, sometimes mixing with pollutants to reduce visibility but generally dissipating quickly with daytime heating.