The air quality in South Korea, particularly within the densely populated Seoul Metropolitan Area, is frequently among the worst for developed nations, presenting a significant public health challenge. This issue is a complex product of geography, climate, domestic industrial activity, and the long-range transport of pollutants. The persistent haze and high concentrations of fine dust result from a combination of external emissions carried across the sea and the structural limitations of South Korea’s own energy and urban planning. Understanding the severity of the air quality problem requires examining the interplay between foreign sources, internal contributors, and the atmospheric conditions that trap the resulting pollution.
The Role of Transboundary Sources
Transboundary air pollution represents a dominant factor contributing to South Korea’s poor air quality, especially during certain seasons. Prevailing westerly and northwesterly winds serve as the primary mechanism, carrying pollutants from the industrial heartlands of neighboring regions across the Yellow Sea. These winds are particularly strong during the winter and spring, leading to increased fine dust concentrations in the Korean Peninsula.
Studies show that during periods of high concentration, foreign sources can account for a substantial percentage of Fine Particulate Matter (PM2.5) in South Korea. On days with the worst air quality, external contributions are often estimated to be as high as 60% to 80% of the total PM2.5 levels. The main sources of these transported aerosols are the vast industrial and coal-fired power operations located to the west of the peninsula.
This long-range transport involves both primary pollutants and the gaseous precursors that form secondary aerosols during the journey. The phenomenon known as “Yellow Dust” or Hwangsa further exacerbates the situation, particularly in spring. While this dust originates naturally from the Gobi Desert, the airborne particles often mix with and carry additional anthropogenic pollution from industrial areas as they travel toward the Korean Peninsula. The combined effect of natural dust and industrial plumes significantly elevates the particulate matter concentration reaching South Korea’s western coast and major urban centers.
Key Domestic Contributors to Emissions
While transboundary sources are a major concern, South Korea’s internal economic structure also generates substantial air pollution. A significant domestic contributor is the country’s reliance on coal-fired power plants, which account for a large portion of the nation’s electricity generation. Many of these 57 operational coal plants are located along the western and southern coasts, often near major population centers, concentrating their emissions domestically.
The heavy manufacturing sector, a pillar of the South Korean economy, also produces significant emissions from its industrial smokestacks. Beyond large-scale industry, vehicle emissions, particularly from older diesel vehicles, remain a persistent source of local air pollution in urban areas. Motor vehicle emissions are a major source of PM2.5, especially in the Seoul Metropolitan Area.
Localized activities contribute seasonally, especially during colder months. Residential heating systems, including boilers, and the use of solid fuels release a variety of pollutants into the low-lying urban air. This combination of dense population, high-traffic volume, and concentrated power generation creates a complex network of internal pollution sources that compound the effects of transboundary transport.
Geographic and Climatic Accumulation Factors
The unique geography and meteorological conditions of the Korean Peninsula play a significant role in trapping pollutants, preventing their dispersal. South Korea is frequently affected by specific high-pressure systems that create atmospheric stagnation, especially during winter and spring. This results in weak wind speeds and a low mixing layer, meaning pollutants are not effectively ventilated away from the ground.
The formation of a temperature inversion layer, where warmer air sits above cooler air, acts like a lid over urban areas, trapping air pollution near the surface. This phenomenon is particularly problematic for densely populated urban basins like Seoul, which are naturally constrained by surrounding mountainous terrain. The surrounding mountains physically impede the horizontal movement of air, exacerbating the concentration of both locally generated and externally transported fine dust.
When prevailing westerly winds carry pollution, stagnant air masses prevent subsequent eastward flow from clearing the haze. This lack of ventilation means that pollutants, once arrived or generated, can persist for days, leading to prolonged episodes of unhealthy air quality. The topography and frequent stagnant air conditions transform the peninsula into a basin where particulate matter easily accumulates.
The Primary Pollutants and Their Origins
The primary constituent of South Korea’s air quality crisis is Fine Particulate Matter, specifically PM2.5 (inhalable particles with a diameter of 2.5 micrometers or less). These particles are the main concern because their small size allows them to penetrate deeply into the respiratory and circulatory systems, posing serious health risks. While PM10 is also present, the concentration of the finer PM2.5 is the metric most frequently cited for poor air quality.
The chemical composition of PM2.5 links them directly back to major source categories. A large fraction of the particulate matter consists of secondary inorganic aerosols, which are formed in the atmosphere from gaseous precursors, including nitrates, sulfates, and ammonium.
Origins of PM2.5 Components
The specific chemical components trace back to distinct emission sources:
Sulfates and secondary sulfates originate from sulfur dioxide (SO2) emissions from the combustion of coal and heavy fuel oil, pointing to both transboundary industrial sources and domestic coal-fired power plants. Nitrates are formed from nitrogen oxides (NOx), which are largely emitted by high-temperature combustion sources like vehicle engines and power generation. Organic carbon and black carbon, products of incomplete combustion from vehicles, biomass burning, and industrial processes, also contribute significantly to the overall PM2.5 mass.