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Tsushima City, nestled within Nagasaki Prefecture, Japan, occupies the majority of Tsushima Island and several smaller surrounding islets. Its geography is dramatically shaped by its position in the Korea Strait, separating Japan from the Korean Peninsula. The island is predominantly mountainous, with elevations reaching around 500 meters, creating a complex terrain that influences air circulation. The coastline is deeply indented with numerous bays and inlets, providing natural harbours but also limiting atmospheric dispersion in those areas. Tsushima’s urban character is defined by a dispersed settlement pattern, with the main city centre and smaller communities scattered along the coastal plains. The surrounding landscape is a mix of evergreen forests, agricultural land – primarily small-scale farming – and rugged coastline. While not a major industrial hub, Tsushima has historically relied on fishing and more recently, tourism. The urban-rural gradient is quite steep; moving inland quickly transitions from populated areas to dense woodland. This proximity to the open sea generally provides good ventilation, but localized topographic features can trap pollutants during calm conditions. The island’s position also means it’s susceptible to air masses originating from both the Asian continent and the Pacific Ocean, carrying pollutants from distant sources.

Tsushima’s air quality follows a distinct seasonal pattern. Spring (March-May) sees an increase in particulate matter from long-range transport of dust storms originating in the Gobi Desert and the Korean Peninsula, exacerbated by winds. Pollen from local vegetation also contributes to discomfort for allergy sufferers. Summers (June-August) are typically the cleanest, benefiting from prevailing southwesterly winds that sweep pollutants out to sea and frequent rainfall which effectively scrubs the atmosphere. However, humidity can contribute to secondary pollutant formation. Autumn (September-November) often experiences temperature inversions, trapping pollutants in the valleys and coastal areas, particularly as heating begins. Typhoons, common during this season, can temporarily improve air quality through strong winds and rain, but also stir up dust and debris. Winters (December-February) are characterized by cold, dry air and stable atmospheric conditions, leading to a build-up of pollutants from local heating sources. Siberian air masses can bring periods of very cold, stagnant air. Sensitive groups – the elderly, children, and those with respiratory conditions – should limit strenuous outdoor activity during spring dust events and autumn/winter stagnation periods. Monitoring wind direction and avoiding activity near busy roads is advisable year-round.