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Shanghai, situated at the mouth of the Yangtze River on China's eastern coast, occupies a strategic position within the Yangtze River Delta economic zone, one of the world's most densely populated and industrialized regions. The city's geography is predominantly flat, with an average elevation of just 4 meters above sea level, sprawling across the alluvial plain formed by the Yangtze's sediment deposits. This low-lying terrain, combined with its location between the East China Sea to the east and the vast Yangtze River Basin to the west, creates a unique environmental context that profoundly influences air quality. Shanghai's urban core, characterized by its iconic skyline along the Huangpu River, transitions rapidly into suburban and then rural areas, though the urban-rural gradient is increasingly blurred by continuous expansion. The city is encircled by water bodies—including the Yangtze Estuary, Hangzhou Bay, and numerous canals—which can moderate temperatures but also trap pollutants under certain meteorological conditions. Proximity to major shipping lanes and the bustling Port of Shanghai, one of the world's busiest, contributes significantly to emissions, while the surrounding region hosts extensive industrial belts, particularly in sectors like petrochemicals, steel, and manufacturing. This industrial backdrop, coupled with high population density and vehicle traffic, creates a complex pollution landscape where geographic features like the river valley and coastal breezes interact with anthropogenic sources to shape air quality challenges.

Shanghai's air quality follows a distinct seasonal pattern driven by its humid subtropical climate and monsoon influences. In winter, from November to February, pollution peaks due to a combination of factors: increased emissions from heating sources, frequent temperature inversions that trap pollutants near the ground, and prevailing northerly winds that transport industrial emissions from inland regions. This period sees higher levels of PM2.5 and other particulates, making it the least favourable time for outdoor activities, especially for sensitive groups like children, the elderly, and those with respiratory conditions who should limit exposure and use air purifiers indoors. Spring brings gradual improvement as temperatures rise and southeasterly winds from the ocean help disperse pollutants, though occasional dust storms from northern China can cause temporary spikes. Summer, from June to August, offers the best air quality due to strong monsoon rains that wash pollutants from the atmosphere and consistent sea breezes that enhance ventilation; however, extreme heat and humidity can exacerbate ozone formation, posing risks during midday hours. Autumn starts with relatively clean air but transitions to worsening conditions as wind patterns shift and atmospheric stability increases. Throughout the year, weather hazards like typhoons in late summer can temporarily clear the air but bring other risks, while fog and high humidity in cooler months often coincide with pollution episodes, reducing visibility and air quality.