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Nagato, nestled along the western coast of Yamaguchi Prefecture, Japan, occupies a unique and geographically complex position. Situated at approximately 34.37°N, 131.18°E, the city’s landscape is dramatically shaped by the Japan Sea and the surrounding mountainous terrain. The urban area is a relatively narrow strip hugging the coastline, transitioning rapidly into steep, forested slopes that rise sharply inland. This topography significantly influences local air circulation patterns. The city’s elevation varies considerably, ranging from sea level along the coast to over 800 meters in the higher reaches of the surrounding mountains. This elevation gradient contributes to localized temperature inversions, particularly during the cooler months, trapping pollutants closer to the ground. The proximity to the Japan Sea introduces a maritime influence, with prevailing winds often carrying moisture and impacting the dispersion of airborne particles. While Nagato isn't directly adjacent to major industrial belts, it lies within a region with agricultural activity, primarily rice cultivation, which can contribute to ammonia emissions. The urban–rural gradient is quite sharp; beyond the coastal settlements, the landscape quickly reverts to rural farmland and dense forests. The surrounding landscape is dominated by the Chugoku Mountains, providing a natural barrier that can both protect and concentrate air pollutants depending on prevailing wind conditions. The city’s coastal location also means it is susceptible to sea salt aerosols, which can impact respiratory health and contribute to particulate matter.

Nagato’s air quality experiences a distinct seasonal cycle heavily influenced by its coastal location and mountainous terrain. Winter (December-February) typically presents the most challenging conditions. Cold, stable air masses frequently settle over the region, leading to temperature inversions that trap pollutants near the surface. Reduced wind speeds during this period further exacerbate the problem, limiting dispersion. Fog, common in winter, also contributes to the concentration of particulate matter. Spring (March-May) brings a gradual improvement as temperatures rise and winds increase, helping to clear the air. However, pollen season can significantly impact air quality, triggering respiratory sensitivities. Summer (June-August) is generally the cleanest period, characterized by strong sea breezes that effectively ventilate the area. The monsoon season brings frequent rainfall, washing pollutants from the atmosphere. Autumn (September-November) sees a transition period. While winds remain relatively strong, cooler temperatures can occasionally trigger localized inversions, particularly in the evenings. Agricultural activities, such as rice harvesting, can also contribute to short-term spikes in particulate matter and ammonia. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter months, limiting outdoor activity on days with stagnant air. Spring requires awareness of pollen counts. Overall, the months of July and August offer the most favourable conditions for outdoor pursuits, benefiting from consistent sea breezes and rainfall.