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Bissau, the capital and largest city of Guinea-Bissau, occupies a strategic position on the Atlantic coast at the mouth of the Geba River estuary, creating a unique urban environment where land and water intimately interact. Situated on the Bissau Islands, the city's geography is characterized by low-lying terrain with minimal elevation variation, rarely exceeding 10 meters above sea level, which significantly influences its air quality dynamics. The surrounding landscape consists of mangrove swamps, tidal flats, and alluvial plains that extend inland, with the city serving as the primary urban hub in a predominantly rural country. Bissau's location on the West African coast places it within the Guinea savanna zone, with agricultural activities—primarily rice cultivation, cashew production, and subsistence farming—encircling the urban area, creating a distinct urban–rural gradient. The city's port, a vital economic lifeline, generates emissions that mix with local pollution sources, while the Atlantic Ocean's proximity moderates temperatures but can trap pollutants under specific meteorological conditions. The flat terrain and coastal setting limit natural ventilation, allowing pollutants from vehicle exhaust, road dust, and domestic biomass cooking to accumulate, particularly during the dry season when atmospheric stagnation is common. The urban fabric, with its mix of colonial-era architecture and informal settlements, exacerbates exposure to pollution in densely populated neighborhoods where waste burning and generator use are prevalent.

Bissau's air quality follows a pronounced seasonal pattern driven by the West African monsoon, with pollution peaking dramatically during the dry season from November to February. During these months, the Harmattan winds blow dry, dusty air from the Sahara Desert across the region, combining with local emissions from vehicles, waste burning, and biomass cooking to create hazardous conditions. Temperature inversions are common in the cool, stable atmosphere, trapping pollutants near the ground and reducing dispersion, while low humidity minimizes rainfall that could cleanse the air. Sensitive groups, such as children, the elderly, and those with respiratory conditions, should avoid prolonged outdoor exposure during this period, especially in the early mornings when pollution concentrations are highest. From March to May, the transitional period brings increasing humidity and occasional showers, gradually improving air quality as pollutants are washed away, though generator use during power outages may still cause localized spikes. The rainy season from June to October offers the cleanest air, with frequent downpours and southwesterly monsoon winds effectively scavenging pollutants, making this the optimal time for outdoor activities. However, high humidity can exacerbate mold and allergen issues indoors. Throughout the year, residents should monitor weather forecasts for fog events, which can combine with pollution to reduce visibility and respiratory health, and plan activities for midday when atmospheric mixing is typically better.