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Sendai, the largest city in Japan's Tohoku region, occupies a strategic position along the Pacific coast of Miyagi Prefecture, nestled between the Ōu Mountains to the west and Sendai Bay to the east. This coastal urban centre, often called the 'City of Trees' for its verdant boulevards, sits on the Sendai Plain at a modest elevation averaging around 20 metres above sea level, with terrain gently sloping toward the ocean. Its geography creates a distinct urban–rural gradient, transitioning from dense commercial districts in the city centre to suburban residential areas and then to agricultural zones producing rice and vegetables in the surrounding countryside. Proximity to the Pacific Ocean significantly influences local air quality through sea breezes that typically disperse pollutants, though the city's position within Japan's industrial belt—with nearby manufacturing facilities in areas like Tagajō and Natori—introduces emissions from transportation, energy production, and general urban activities. The surrounding mountains can occasionally trap air masses, particularly during stable weather conditions, leading to temporary pollution accumulation. Sendai's location in a seismically active zone also means occasional dust from construction and recovery efforts, though this is less consistent than industrial or vehicular sources. The city's well-planned urban layout, with extensive green spaces, helps mitigate some pollution impacts, but its role as an economic hub for northeastern Japan ensures ongoing air quality challenges typical of mid-sized metropolitan areas.

Sendai's air quality follows a distinct seasonal pattern shaped by its temperate climate and Pacific influences. In winter (December to February), cold temperatures and occasional temperature inversions can trap pollutants near the ground, particularly during calm, clear nights when heating emissions increase; sensitive groups like those with respiratory conditions should limit prolonged outdoor exposure during these periods. Spring (March to May) brings improving conditions as warming temperatures and more frequent winds from the Pacific help disperse pollutants, making April and May favourable for outdoor activities despite occasional pollen from the region's abundant trees. Summer (June to August) sees the cleanest air overall, with strong sea breezes and the rainy season (typically June to mid-July) washing particulate matter from the atmosphere, though high humidity can sometimes lead to haze formation. Autumn (September to November) begins with relatively good air quality, but as temperatures drop and wind patterns shift, pollution may gradually increase toward late November, especially from increased vehicular traffic and agricultural burning in surrounding areas. Throughout the year, Sendai benefits from the absence of extreme weather hazards like sandstorms or dense industrial smog, but residents should monitor local advisories during stagnant weather conditions. Sensitive individuals are advised to plan outdoor activities for mid-morning to afternoon hours when dispersion is typically best, and to be cautious during early winter mornings and late autumn evenings when inversion layers are most common.