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Osan, nestled within Gyeonggi Province, South Korea, occupies a strategic position in the central part of the Korean Peninsula. Its coordinates (37.1498, 127.0771) place it within a relatively flat, gently undulating landscape, characteristic of the region’s alluvial plains. The city’s elevation is modest, generally below 100 meters, contributing to limited natural dispersion of pollutants. Osan is not directly on the coast, but benefits from proximity to the Yellow Sea, approximately 30 kilometers west, which influences local weather patterns and occasionally delivers maritime air masses. However, this proximity also means susceptibility to sea-land breezes that can trap pollutants. Surrounding Osan are significant industrial zones, notably in nearby Pyeongtaek and Ansan, contributing to regional emissions. The urban-rural gradient is pronounced; to the east and south, the terrain rises into the foothills of the Taebaek Mountains, offering some cleaner air but also creating topographical barriers to air circulation. Agricultural land surrounds parts of the city, but the dominant land use is increasingly urban and industrial, impacting local air quality. The city’s location within a major transportation corridor, serving Seoul and other key cities, further exacerbates pollution levels due to vehicle emissions. This confluence of factors makes Osan a focal point for air quality concerns.

Osan’s air quality follows a distinct seasonal pattern. Spring (March-May) often sees elevated particulate matter due to yellow dust storms originating from the Gobi Desert, carried by prevailing westerly winds. These events, combined with agricultural burning, can significantly degrade air quality. Summer (June-August) brings the monsoon season, offering periods of cleaner air as rainfall effectively washes pollutants from the atmosphere. However, high humidity can also promote secondary pollutant formation. Autumn (September-November) is typically the most pleasant period for air quality, with cooler temperatures and stable atmospheric conditions. However, this stability can also lead to temperature inversions, trapping pollutants near the ground. Winter (December-February) is the most challenging season. Cold, dry air masses from Siberia combine with stagnant high-pressure systems, creating strong temperature inversions that exacerbate pollution from heating sources and industrial activity. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit outdoor exertion during winter and yellow dust events. Months to avoid prolonged outdoor activity are generally January, February, and April. Monitoring air quality forecasts is crucial, particularly during these periods, and using air purifiers indoors is recommended.