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Cocal, Piauí, Brazil, occupies a strategic position within the vast Sertão region, a semi-arid expanse dominating much of the Northeast. Located at approximately -3.4708° latitude and -41.5550° longitude, the city’s geography is defined by its relatively flat terrain, characteristic of the Brazilian Highlands’ lower slopes. The elevation averages around 530 meters above sea level, contributing to a generally stable atmospheric layer, though susceptible to temperature inversions under specific conditions. Cocal sits near the Parnaíba River basin, though the river itself is not immediately adjacent, influencing regional humidity and potential for localized fog formation, particularly during the transition seasons. The surrounding landscape is predominantly *caatinga*, a unique thorny scrub biome adapted to extreme drought, interspersed with patches of gallery forest along ephemeral streams. This vegetation cover, while providing some natural air filtration, can also contribute to particulate matter during the dry season when leaf litter accumulates. Agriculture, particularly soybean and corn cultivation, is a significant economic driver in the area, and the associated machinery and fertilizer use can impact local air quality. The urban–rural gradient around Cocal is relatively sharp; the city transitions quickly into the expansive *caatinga* landscape, meaning agricultural activities and dust from unpaved roads are readily transported into the urban environment. The absence of major industrial belts within the immediate vicinity mitigates some pollution risks, but regional transportation corridors carrying goods to and from larger urban centers contribute to vehicle emissions.

Cocal’s tropical climate dictates a distinct wet and dry season cycle, profoundly influencing air quality patterns. The dry season, typically spanning from June to September, is characterized by intense heat, low humidity, and minimal rainfall. This period often witnesses a noticeable increase in particulate matter concentrations, primarily due to windblown dust from agricultural fields and unpaved roads. The lack of rainfall prevents the natural cleansing effect of precipitation, allowing pollutants to accumulate. Temperature inversions, where a layer of warm air traps cooler air near the ground, are more frequent during these months, exacerbating the problem by preventing vertical dispersion of pollutants. Conversely, the wet season (October to May) brings frequent rainfall and higher humidity, naturally scrubbing the atmosphere and significantly reducing particulate matter. However, periods of intense rainfall can lead to localized flooding, potentially releasing mold spores and other allergens into the air. The transition months (April/May and September/October) are particularly susceptible to fog formation due to the combination of cooler temperatures and relatively high humidity, which can trap pollutants near the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak afternoon heat and avoiding areas with high dust exposure. During the wet season, those with allergies should monitor pollen and mold counts. Maintaining indoor air quality through proper ventilation and air filtration is advisable year-round.