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Hamhung, North Korea's second-largest city, occupies a strategic position in South Hamgyong Province along the eastern coast of the Korean Peninsula. Situated at the mouth of the Songchon River where it meets the Sea of Japan, the city spreads across a coastal plain flanked by the Hamgyong Mountains to the west and north, creating a semi-enclosed basin that profoundly influences its air quality. This topography traps pollutants from the city's extensive industrial belt, which includes major chemical plants, coal-fired facilities, and manufacturing complexes concentrated along the river valley and port areas. The urban core transitions rapidly to agricultural zones in the surrounding plains, where rice paddies and farmland dominate, though this rural-urban gradient does little to mitigate the industrial emissions that characterize Hamhung. At approximately 40 meters above sea level, the city's low elevation combined with its proximity to the sea creates frequent fog and humidity that can exacerbate pollution episodes. The port of Hungnam, part of Hamhung's metropolitan area, adds maritime emissions to the mix, while road dust from the city's infrastructure and vehicle exhaust from limited transportation networks contribute to particulate matter. The surrounding mountains act as a barrier to westerly winds, often causing stagnant air conditions that allow pollutants to accumulate rather than disperse, making Hamhung's geography a key determinant of its persistent air quality challenges.

Hamhung's continental monsoon climate drives distinct seasonal variations in air quality, with pollution peaking dramatically during the cold months from November through February. In winter, extreme cold triggers widespread residential coal heating, while temperature inversions—common in the city's basin-like terrain—trap industrial emissions from coal-fired plants and chemical facilities near the surface, creating hazardous smog episodes. Sensitive groups, such as children, the elderly, and those with respiratory conditions, should avoid prolonged outdoor activity during these months and consider wearing masks. Spring brings some relief as increasing temperatures and occasional winds from the Sea of Japan help disperse pollutants, though road dust from thawing ground and agricultural activities can maintain moderate pollution levels. Summer offers the cleanest air, with the East Asian monsoon bringing southeasterly winds and rainfall that scrub the atmosphere, though typhoons from the Pacific—peaking in August—can cause temporary spikes in pollution due to stirred-up debris and industrial disruptions. Autumn sees a gradual return of pollution as temperatures drop and heating resumes, with October often marking the transition to winter haze. For optimal outdoor conditions, visitors and residents should favour June through September, while remaining cautious of typhoon-related weather hazards that may impact air quality briefly.