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Sanuki sits nestled within the fertile expanse of the Sanuki Plain in Kagawa Prefecture, serving as a pivotal agricultural heartland on the island of Shikoku. Its geography is defined by a gentle slope descending from the rugged mountains of the south toward the serene shores of the Seto Inland Sea to the north. This specific positioning creates a unique urban-rural gradient where small residential clusters are interspersed with vast rice paddies and onion fields, reducing the dense heat-island effect typical of larger Japanese metropolises. The city's elevation remains relatively low, allowing maritime breezes to sweep across the plains, which generally facilitates the dispersal of local pollutants. However, this same topography can occasionally trap stagnant air during temperature inversions, particularly in the depressions between the hills. The surrounding landscape is devoid of heavy industrial belts, meaning the primary air quality drivers are mobile sources from regional transit and seasonal agricultural activities. The proximity to the Seto Inland Sea provides a moderating influence on temperature and humidity, yet it also exposes the region to saline aerosols. Because the city lacks a massive concrete core, the natural vegetation acts as a biological filter, scrubbing particulate matter from the air. Consequently, Sanuki maintains a character of rural tranquility, where the air quality is largely dictated by the interplay between the Pacific moisture, the protective mountain barriers to the south, and the periodic influx of continental air masses from the west and north.

Sanuki’s air quality follows a distinct seasonal rhythm dictated by the East Asian monsoon and regional meteorological shifts. Spring is often the most challenging period, as the city is susceptible to Kosa, or yellow dust, blowing from the Gobi Desert. These transboundary particulate events, peaking in March and April, can spike PM2.5 levels, necessitating caution for those with asthma or chronic respiratory conditions. As the region transitions into summer, high temperatures and intense solar radiation trigger the photochemical production of ground-level ozone. This period, particularly in July and August, sees a rise in smog during stagnant afternoons, making early morning or late evening the ideal times for outdoor activity. Autumn brings a refreshing shift; as the monsoon weakens and cooler, drier air arrives from the north, the atmosphere clears, offering the year's most pristine air quality. This is the optimal window for hiking the southern foothills. Winter is generally mild, but the occurrence of temperature inversions can trap local emissions from residential heating and vehicle exhaust near the ground. During these cold snaps in December and January, air can become stagnant, leading to localized concentrations of pollutants. Sensitive groups should monitor local advisories during the spring dust storms and summer ozone peaks. By understanding these cycles, residents can navigate the year, favoring the crisp clarity of November for outdoor exercise while remaining vigilant during the hazy transitions of the early spring months.