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Nemuro, nestled on the eastern coast of Hokkaido, Japan, occupies a unique and challenging geographic position. Situated at 43.33°N, 145.58°E, the city’s landscape is dramatically shaped by the Sea of Okhotsk and the Nemuro Peninsula, a rugged extension of the Hokkaido mainland. The terrain is characterized by a gradual rise from the coastline, transitioning into rolling hills and eventually the more substantial peaks of the Hidaka Mountains to the west. This coastal location exposes Nemuro to persistent northerly winds, a crucial factor in its air quality dynamics. The surrounding landscape is a blend of coastal plains, agricultural fields (primarily barley and potatoes), and dense coniferous forests, creating a distinct urban–rural gradient. While Nemuro itself is a relatively small city with a population of approximately 27,109, it serves as a significant fishing port and gateway to the Shiretoko Peninsula, a UNESCO World Heritage site. There are no major industrial belts immediately adjacent to Nemuro; however, the broader Hokkaido region has some resource extraction and agricultural processing, which can contribute to regional air pollution transported by prevailing winds. The city’s elevation, averaging around 10-30 meters above sea level, minimizes the potential for significant terrain-induced air stagnation, but the proximity to the cold Sea of Okhotsk frequently generates fog and low-lying cloud cover, impacting pollutant dispersion. The coastal environment, combined with the surrounding agricultural and forested areas, creates a complex interplay of factors influencing local air quality.

Nemuro’s air quality experiences a distinct seasonal cycle heavily influenced by its maritime climate and prevailing winds. Winter (December-February) presents the most challenging period. Cold, stable air masses originating over the Sea of Okhotsk frequently lead to temperature inversions, trapping pollutants near the ground. Fog, a common occurrence during these months, further exacerbates the situation by reducing atmospheric mixing and hindering pollutant dispersal. While industrial emissions are relatively low locally, particulate matter from residential heating (primarily wood and kerosene) and agricultural activities can accumulate. Spring (March-May) brings a gradual improvement as temperatures rise and winds increase, breaking up inversions and dispersing pollutants. However, pollen levels from blooming vegetation can become a significant irritant. Summer (June-August) generally offers the best air quality, with strong, consistent northerly winds effectively flushing out any accumulated pollutants. Occasional periods of stagnant weather can still occur, but are less frequent. Autumn (September-November) sees a transition period, with decreasing temperatures and increasing fog, leading to a gradual decline in air quality towards winter conditions. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during winter months, limiting outdoor exposure on foggy days and avoiding strenuous activity. During pollen season, wearing a mask can mitigate allergic reactions. Overall, the city’s air quality is generally good, but awareness of seasonal variations is crucial for protecting public health.