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Piracuruca, nestled in the southeastern region of Piauí state, Brazil, occupies a geographically significant position within the larger São Francisco River basin. Located at approximately -3.9278° latitude and -41.7089° longitude, the city’s terrain is characterized by undulating plains, typical of the Cerrado biome transitioning towards Caatinga influences. The elevation averages around 500 meters above sea level, contributing to a relatively stable atmospheric layer, though susceptible to temperature inversions under specific conditions. The surrounding landscape is a mosaic of semi-arid scrubland, interspersed with pockets of agricultural activity, primarily focused on rain-fed subsistence farming and, increasingly, irrigated crops benefiting from access to the São Francisco River. This river, a vital lifeline for the region, flows relatively close to Piracuruca, moderating local temperatures and influencing humidity levels. The urban–rural gradient is gradual, with small settlements and agricultural fields extending outwards from the city center. While Piracuruca isn't situated within a major industrial belt, the presence of small-scale agricultural processing facilities and vehicle traffic contribute to localized air pollution. The prevailing winds generally flow from the northeast, carrying potential pollutants from surrounding agricultural areas and impacting air quality within the city. The city’s location within a transitional biome means it experiences a unique combination of dry and humid conditions, influencing the dispersion of airborne particles and gases. The relatively flat terrain can also exacerbate the accumulation of pollutants, particularly during periods of stagnant air.

Piracuruca’s tropical climate dictates a distinct wet and dry season pattern, profoundly impacting air quality throughout the year. The dry season, typically spanning from May to September, is characterized by intense solar radiation, low humidity, and frequent dust storms originating from the surrounding Cerrado and Caatinga landscapes. These events significantly elevate particulate matter concentrations, particularly PM10 and PM2.5, posing a respiratory health risk. The lack of rainfall during this period also limits the natural cleansing of the atmosphere. Conversely, the wet season, from October to April, brings increased rainfall and higher humidity, generally leading to improved air quality as precipitation washes away pollutants and increased moisture traps particulate matter. However, periods of prolonged fog, common during the transition months (October-November and March-April), can trap pollutants near the ground, creating localized episodes of poor air quality. Temperature inversions, though less frequent than in colder climates, can occur during the dry season, trapping pollutants in a stable layer close to the surface. The months of July and August often experience the highest levels of dust and particulate matter due to the combined effects of dry conditions and wind patterns. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit outdoor activity during these periods. During the wet season, while overall air quality improves, individuals with allergies may experience increased symptoms due to pollen and mold spores.