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Hailin is a county-level city in southeastern Heilongjiang province, situated in the Changbai Mountains region near the border with Jilin province. Nestled at coordinates 44.5940°N, 129.3800°E, the city occupies a transitional zone between the mountainous terrain of the Changbai range and the Songnen Plain to the northwest, with an average elevation of approximately 300 meters above sea level. This positioning creates a distinct urban-rural gradient where Hailin serves as an administrative and economic hub for surrounding agricultural communities, while maintaining proximity to forested mountain areas. The city lies approximately 150 kilometers southwest of Mudanjiang, the regional center, and sits within the watershed of the Mudan River system, though no major water bodies directly border the urban core. Hailin's air quality is influenced by its location in a basin-like topography surrounded by low mountains, which can trap pollutants under certain meteorological conditions. The region forms part of Northeast China's agricultural belt, with surrounding areas dedicated to grain production, particularly corn and soybeans, whose seasonal burning practices contribute to regional haze. Urban pollution sources are typical for a Chinese county-level city of nearly 300,000 residents, including vehicular emissions, residential heating during the long winter, and small-scale industrial activities concentrated in peripheral zones. The city's position away from major industrial corridors like the Harbin-Changchun megalopolis provides some insulation from heavy industrial pollution, but its topographic setting creates microclimatic conditions that affect pollutant dispersion.

Hailin experiences distinct seasonal air quality patterns shaped by its continental monsoon climate with long, cold winters and short, warm summers. Winter (December-February) brings the most challenging conditions as temperature inversions frequently develop in the mountain-basin topography, trapping pollutants from coal-fired heating systems and vehicle emissions. Cold, stagnant air masses combined with residential heating create persistent haze episodes, particularly in January when temperatures plummet below -20°C. Sensitive groups should limit prolonged outdoor exposure during these months and consider using air purifiers indoors. Spring (March-May) begins with lingering winter pollution that gradually improves as temperatures rise and winds increase, though March can still see poor air quality from dust storms originating in Mongolia and western China. April and May offer better conditions as increased precipitation helps cleanse the atmosphere. Summer (June-August) provides the cleanest air with frequent rainfall, southeasterly monsoon winds from the Sea of Japan, and good atmospheric mixing, making this the optimal season for outdoor activities. Autumn (September-November) sees a gradual deterioration as temperatures drop, heating systems activate, and atmospheric stability increases. October and November often experience pollution buildup before winter's peak, with agricultural burning in surrounding areas occasionally contributing to regional haze. Throughout the year, morning fog is common due to the city's river valley location, which can temporarily elevate particulate concentrations until daytime heating disperses the moisture.