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Ōta-ku occupies Tokyo's southernmost ward, stretching from the Tama River's estuary along Tokyo Bay to inland urban districts, creating a distinctive geographic duality that profoundly influences its air quality. Situated on the Kantō Plain at minimal elevation averaging just 3-5 meters above sea level, this flat terrain inhibits natural air drainage and promotes pollutant accumulation. The ward's western boundary follows the Tama River, while its eastern edge meets Tokyo Bay—this coastal positioning subjects Ōta-ku to both marine breezes that can disperse pollutants and sea-salt aerosols that occasionally exacerbate particulate matter. As part of Tokyo's Keihin Industrial Zone, Ōta-ku hosts Haneda Airport (Japan's busiest), multiple industrial complexes along its waterfront, and dense residential corridors, creating an intense urban-rural gradient where pollution sources concentrate near transportation hubs and manufacturing districts. The ward's location within the Greater Tokyo Area's southern corridor places it downwind of regional pollution flows from Kawasaki and Yokohama's industrial belts, particularly when northwesterly winds prevail. This geography—flat, coastal, and industrially active—creates a microenvironment where local emissions from transportation and industry interact with regional pollution transport, while the lack of topographic relief and proximity to water bodies generates complex atmospheric conditions that alternately trap or disperse contaminants depending on seasonal weather patterns.

Ōta-ku's air quality follows Tokyo's seasonal rhythm with distinct variations that sensitive residents should monitor carefully. Spring (March-May) brings moderate conditions as increasing daylight and occasional rain showers help disperse pollutants, though late March can see temporary spikes from increased construction activity and pollen season—asthmatics should monitor forecasts during this transition period. Summer (June-August) offers generally favorable air quality despite high humidity, as southerly Pacific breezes from Tokyo Bay ventilate the ward and frequent rainfall scrubs particulate matter from the atmosphere; however, ozone levels may rise on hot, stagnant afternoons, making early morning the optimal time for outdoor exercise. Autumn (September-November) begins cleanly but deteriorates gradually as temperatures drop, with October-November often seeing the year's worst pollution episodes due to temperature inversions that trap vehicle and industrial emissions under still, cool air—this is when sensitive groups should limit prolonged outdoor exposure and use air purifiers indoors. Winter (December-February) maintains stable but elevated pollution levels as cold, dry conditions from the Asian continent combine with increased heating emissions and reduced atmospheric mixing, creating persistent haze that lingers until spring winds arrive. Throughout the year, Haneda Airport's operations contribute consistent background pollution, while weather patterns like the winter monsoon and summer typhoons alternately concentrate or cleanse the air in predictable seasonal cycles.