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Lalo sits within the Couffo Department of southern Benin, characterized by a low-lying topography that defines the region's hydrological and atmospheric behavior. Positioned in a transition zone between the coastal plains and the interior plateaus, the city is deeply embedded in the fertile Mono River basin, where the lush, alluvial soils support intensive agricultural activity. The urban character of Lalo is a blend of concentrated residential clusters and sprawling rural hinterlands, creating a porous urban-rural gradient. This lack of dense industrialization means that air quality is primarily influenced by the surrounding landscape rather than factory emissions. The terrain is predominantly flat, which prevents the formation of significant wind barriers, allowing air masses to move relatively freely across the plains. However, this flatness also facilitates the accumulation of particulate matter during periods of atmospheric stagnation. The proximity to dense palm groves and maize fields introduces significant organic aerosols into the air, particularly during harvest cycles. Because Lalo lacks high-elevation relief, it does not experience the dramatic rain-shadow effects seen in mountainous regions, but it is highly susceptible to the moisture-laden winds from the Atlantic. The interaction between the humid riverine environment and the dusty interior creates a unique atmospheric profile where humidity often traps ground-level pollutants, particularly during the early morning hours, leading to localized haze that lingers over the city's central markets and residential zones, impacting the overall breathing environment for the local population.

In Lalo, air quality is dictated by the rhythmic oscillation between the dry and wet seasons. From December to March, the region is dominated by the Harmattan, a dry, northeasterly trade wind that carries vast quantities of mineral dust from the Sahara Desert. During these months, particulate matter peaks, creating a persistent haze that reduces visibility and irritates the respiratory systems of the inhabitants. This period is the most hazardous for sensitive groups, such as children and the elderly, who should limit prolonged outdoor exertion during peak dust events. As the climate transitions into the first rainy season from April to July, the precipitation effectively scrubs the atmosphere, washing away airborne dust and lowering pollution levels. However, the humidity can trigger mold spores and other biological allergens. A brief dry spell in August often sees a spike in agricultural burning as farmers clear land, releasing smoke and carbon monoxide into the stagnant air. The second rainy season, from September to October, returns the air to its cleanest state. Temperature inversions are rare but can occur during cool December nights, trapping smoke from charcoal cooking fires near the ground. To maintain health, residents are advised to avoid outdoor activities during the height of the Harmattan and to be mindful of smoke inhalation during the August burning window, ensuring that ventilation is maximized in homes to clear domestic biomass emissions to protect long-term pulmonary health.