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Cornillon, nestled within the Ouest department of Haiti (coordinates 18.6755, -71.9527), presents a compelling case study in urban geography and its influence on air quality. Situated on the southwestern slopes of the Massif de la Hotte, a rugged mountain range, the city’s terrain is characterized by steep inclines and valleys, significantly impacting air circulation patterns. Cornillon’s elevation, while not exceptionally high, contributes to localized temperature inversions, particularly during the drier months, trapping pollutants closer to the ground. The city’s proximity to the Caribbean Sea, approximately 20 kilometers to the south, introduces a maritime influence, bringing humidity and occasional sea breezes that can disperse pollutants, but also contribute to coastal fog events. The surrounding landscape is a mosaic of small-scale agriculture – primarily coffee, mango, and plantain cultivation – and patches of secondary forest. This agricultural activity, while vital to the local economy, can be a source of particulate matter from burning agricultural waste. The urban–rural gradient around Cornillon is relatively sharp; the city transitions quickly into rural agricultural lands and then into the mountainous terrain of the Massif de la Hotte. There are no major industrial belts immediately adjacent to Cornillon, but the larger urban center of Les Cayes, with its port and associated industries, lies approximately 30 kilometers to the east, potentially influencing regional air quality through long-range transport of pollutants. The valley location also concentrates any emissions, limiting natural ventilation.

Cornillon’s tropical climate dictates a wet and dry season cycle, profoundly influencing its air quality profile. The dry season, typically spanning from December to April, is often characterized by reduced rainfall and increased sunshine, leading to lower humidity. However, this period also sees a greater propensity for temperature inversions, where cooler air becomes trapped beneath a layer of warmer air, hindering vertical mixing and concentrating pollutants near the surface. Agricultural burning, a common practice for land clearing and waste disposal, intensifies during this time, releasing significant amounts of particulate matter and contributing to hazy conditions. The months of January and February are particularly susceptible to these conditions. Conversely, the wet season (May to November) brings frequent rainfall and higher humidity, which naturally scavenges pollutants from the atmosphere, leading to improved air quality. Stronger winds associated with tropical disturbances and occasional storms further aid in dispersion. Fog events, common along the coast, can also temporarily reduce visibility and trap pollutants in localized areas. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting strenuous outdoor activities during peak pollution periods, typically mid-morning and early afternoon. During the wet season, while overall air quality is generally better, periods of heavy rainfall can lead to increased mold and mildew, impacting indoor air quality and potentially exacerbating respiratory issues.