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Ning'an is a county-level city situated in southeastern Heilongjiang Province, China, nestled within the Changbai Mountain foothills near the border with Jilin Province. Its coordinates at 44.3410°N, 129.4830°E place it in a transitional zone between the Northeast China Plain and the mountainous terrain to the east, with an average elevation of approximately 300 meters above sea level. The city lies along the Mudan River, a tributary of the Songhua River, which influences local humidity and fog formation. Geographically, Ning'an is positioned within the Songnen Plain's eastern edge, surrounded by agricultural lands dedicated to corn, soybeans, and rice cultivation, interspersed with forested areas from the nearby Wandashan Range. This urban-rural gradient means air quality is shaped by both urban emissions from its population of over 322,000 and agricultural activities, including biomass burning during harvest seasons. Proximity to major industrial belts is limited, with the nearest significant industrial centers being Mudanjiang City to the north and Jilin City to the south, but regional transport can carry pollutants. The terrain, characterized by rolling hills and river valleys, can trap pollutants under certain meteorological conditions, particularly during temperature inversions in colder months. The city's location in East Asia's temperate monsoon zone means it experiences distinct seasonal shifts that directly impact pollution dispersion, with its inland position reducing maritime influences but allowing for continental air masses to dominate, affecting particulate matter levels from both local and transboundary sources.

In Ning'an, air quality follows a pronounced seasonal pattern driven by the temperate monsoon climate, with pollution typically peaking during winter and early spring. Winter, from December to February, sees the highest pollution levels due to coal burning for heating, combined with frequent temperature inversions that trap pollutants near the surface, leading to haze episodes; sensitive groups like children, the elderly, and those with respiratory conditions should limit outdoor activities during these months. Spring, from March to May, brings gradual improvement as temperatures rise and winds increase, though dust storms from the Gobi Desert can occasionally elevate particulate matter, making late spring more favourable for outdoor pursuits. Summer, from June to August, offers the cleanest air, with monsoon rains and higher wind speeds effectively dispersing pollutants, making it the optimal season for outdoor activities, although humidity can sometimes contribute to fog formation that may briefly reduce visibility. Autumn, from September to November, sees a return to moderate pollution levels as agricultural burning after harvests adds to urban emissions, with cooler temperatures and reduced wind speeds allowing pollutants to accumulate; health guidance recommends monitoring air quality reports during this transition period. Throughout the year, meteorological factors such as low wind speeds in winter, seasonal fog, and the influence of the East Asian monsoon play key roles in shaping AQI fluctuations, with sensitive individuals advised to use air purifiers indoors during peak pollution months and plan outdoor activities for summer or late spring when conditions are most favourable.