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San Juan y Martínez is situated in the westernmost reaches of Cuba, nestled within the fertile plains of the Pinar del Río province. This region is globally renowned as the heartland of premium tobacco production, a factor that profoundly shapes its urban character and environmental profile. The town occupies a low-lying terrain characterized by rich, red soils and a gentle gradient that leads toward the iconic limestone mogotes of the nearby Viñales Valley. Geographically, it serves as a critical node between the coastal plains and the interior highlands, positioned where the Caribbean trade winds consistently sweep across the landscape. This open topography generally facilitates excellent ventilation, preventing the stagnation of pollutants. However, the urban-rural gradient is blurred here, as the town center is tightly integrated with vast agricultural zones. The lack of heavy industrial belts means that the primary air quality drivers are not chemical emissions but rather organic and combustion-based sources. Proximity to small river systems and the high moisture content of the surrounding tropical vegetation help regulate local temperatures, yet the low elevation makes the area susceptible to humidity-driven haze. The surrounding landscape is a mosaic of tobacco plantations and hardwood forests, which act as natural carbon sinks but also contribute to seasonal particulate loads during land preparation. Consequently, the air quality in San Juan y Martínez is fundamentally tied to the agricultural calendar and the rhythmic flow of the Atlantic winds that define this unique western Cuban geography.

The air quality narrative of San Juan y Martínez is dictated by the tropical dichotomy of the wet and dry seasons. During the dry season, spanning from November to April, the region experiences its most significant air quality fluctuations. This period coincides with the critical tobacco land preparation phase, where biomass burning is frequently employed to clear fields. These agricultural fires, combined with lower humidity and occasional temperature inversions, can lead to peaks in particulate matter, creating a smoky haze that lingers in the lowlands. Residents and sensitive groups, particularly those with asthma, should exercise caution during January and February when burning is most intense. Conversely, the wet season, from May to October, brings a dramatic cleansing effect. Frequent, heavy precipitation and tropical storms effectively scrub the atmosphere of airborne pollutants and dust, leading to the lowest pollution troughs of the year. The prevailing northeast trade winds, known as the Aliseos, remain a constant purifying force, though their intensity varies. During the humid summer months, the primary concern shifts from smoke to high atmospheric moisture, which can trap ground-level pollutants from older diesel vehicle emissions. For outdoor activities, the late autumn and spring months offer the most balanced conditions. Health guidance for the elderly and children emphasizes limiting prolonged outdoor exposure during the early morning hours of the dry season when stagnant air and smoke concentrations are typically at their highest levels.