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Saint-Louis du Sud, nestled on Haiti’s southern coast in the Sud department, occupies a geographically significant position where the fertile plains meet the Caribbean Sea. Located at approximately 18.26° N, 73.54° W, the city’s elevation is relatively low, averaging around 10 meters above sea level, contributing to a warm, humid climate and limited vertical mixing of air pollutants. The surrounding landscape is dominated by agricultural land, primarily sugarcane fields and small-scale farming, interspersed with patches of coastal forest. This proximity to agricultural zones introduces potential sources of particulate matter from burning and fertilizer use. The city’s coastal location means it’s susceptible to sea breezes, which can both disperse pollutants and, under certain conditions, trap them, particularly during periods of calm weather. The urban fabric of Saint-Louis du Sud is characterized by a mix of traditional Creole architecture and more modern constructions, reflecting its historical role as a trading port and regional hub. The urban–rural gradient is relatively sharp, with agricultural activities quickly reclaiming land just beyond the city limits. There's a limited industrial presence within Saint-Louis du Sud itself, but nearby areas may host small-scale processing facilities related to agriculture, potentially contributing to localized air pollution. The terrain is generally flat, which, while facilitating urban development, can also hinder the natural dispersion of pollutants, especially when coupled with temperature inversions. The Caribbean Sea acts as a moderating influence on temperature, but also introduces the possibility of salt spray and marine aerosols impacting air quality.

Saint-Louis du Sud experiences a tropical climate with distinct wet and dry seasons, significantly influencing its air quality profile. The wet season, typically from May to October, brings frequent rainfall and increased humidity. While rain can help to cleanse the atmosphere by removing particulate matter, the associated cloud cover can also trap pollutants, particularly during periods of stagnant air. The dry season, from November to April, is characterized by lower rainfall and higher temperatures. This often leads to a build-up of pollutants, especially during the hottest months (March and April), as reduced rainfall limits natural cleansing and increased solar radiation promotes photochemical reactions, potentially forming ground-level ozone. Calm periods during the dry season can result in temperature inversions, where a layer of warm air sits above cooler air near the ground, preventing vertical mixing and trapping pollutants close to the surface. Sea breezes, common throughout the year, generally provide some ventilation, but their effectiveness is reduced during periods of low wind speed. During the wet season, increased agricultural activity, including burning of fields, can contribute to elevated particulate matter levels. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, particularly during periods of stagnant air and high temperatures. Outdoor activities are generally more favourable during the wetter months, although vigilance regarding potential agricultural burning is still advised. Fog, though infrequent, can exacerbate air quality issues by trapping pollutants near the ground.