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Kōchi City, the capital of Kōchi Prefecture on Japan's Shikoku Island, occupies a distinctive coastal position along the Pacific Ocean's Tosa Bay, with the urban core nestled between the ocean to the east and the rugged Shikoku Mountains rising sharply to the west. This geography creates a compressed urban-rural gradient where dense development along the coastal plain transitions rapidly into forested foothills and steep valleys. The city's elevation ranges from sea level to approximately 100 meters in western suburbs, with the surrounding mountains reaching over 1,000 meters, forming a natural barrier that influences local wind patterns. Kōchi's location on the southern coast of Shikoku places it within Japan's subtropical zone, exposed to Pacific weather systems while being somewhat sheltered from continental pollution sources by distance and topography. The urban area is primarily residential and commercial, with limited heavy industry compared to Japan's major industrial belts like Keihanshin or Chūkyō, though general urban emissions from vehicles, construction, and energy use contribute to local air quality. Agricultural zones in surrounding rural areas produce minimal industrial pollution but may contribute seasonal biomass burning. The proximity to the Pacific Ocean generally promotes good air dispersion, but the mountain barrier can occasionally trap pollutants under specific meteorological conditions, particularly during stable atmospheric periods when sea breezes are weak.

Kōchi experiences distinct seasonal air quality patterns shaped by its Pacific coastal climate and monsoon influences. In winter (December-February), cool temperatures and occasional temperature inversions can trap pollutants near the surface, particularly during calm mornings when weak winds from the mountains meet sea breezes, creating stagnation; sensitive groups should limit outdoor exertion on still, foggy days. Spring (March-May) brings improving conditions as increasing solar radiation enhances vertical mixing, though occasional yellow dust (kosa) from continental Asia may drift across the Pacific, typically peaking in April, requiring caution for those with respiratory issues. Summer (June-August) features the rainy season (tsuyu) in June-July, where frequent precipitation scrubs pollutants from the air, resulting in excellent air quality ideal for outdoor activities; however, high humidity and heat in August can exacerbate ozone formation on sunny days, making late afternoon the least favourable time for exercise. Autumn (September-November) offers consistently good air quality as typhoon season passes and stable, clear weather prevails, with October-November being optimal months for outdoor pursuits. Throughout the year, Kōchi's exposure to Pacific winds generally ensures good dispersion, but residents should monitor local advisories during rare episodes of transported pollution or stagnant conditions.