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Pacatu, Bahia, nestled in the semi-arid interior of northeastern Brazil, presents a unique geographic context influencing its air quality. Located at -11.9578, -38.9750, the city sits within the broader Agreste region, a transitional zone between the coastal Mata Atlântica forest and the drier Sertão. The terrain is characterised by rolling hills and plateaus, with elevations ranging between 200-400 meters, contributing to localised temperature inversions. Pacatu isn’t directly adjacent to the coast, but is influenced by prevailing easterly trade winds carrying moisture, though these are often diminished by the time they reach this inland location. The surrounding landscape is dominated by Caatinga scrubland, a resilient but fragile ecosystem. Agriculture, primarily subsistence farming and livestock raising, is prevalent in the surrounding areas, with potential for dust emissions from land management practices. While Pacatu isn’t a major industrial hub, smaller-scale processing of agricultural products contributes to localised emissions. The urban-rural gradient is relatively sharp, with a clear distinction between the concentrated built-up area of Pacatu and the sparsely populated rural hinterland. This gradient impacts pollutant dispersion, concentrating emissions within the city limits during calm conditions. The city’s position within a valley can also trap pollutants, exacerbating air quality issues.

Pacatu experiences a pronounced wet and dry season, dictating the rhythm of air quality. The wet season, typically from April to August, brings relief from dust and particulate matter. Rainfall effectively suppresses dust resuspension from agricultural lands and unpaved roads, leading to improved visibility and cleaner air. However, increased humidity can also foster mould growth, potentially impacting respiratory health. The dry season, spanning September to March, is when air quality concerns peak. Reduced rainfall allows dust and soil particles to become airborne, exacerbated by strong winds common during this period. Temperature inversions, frequently occurring during the cooler nights of the dry season, trap pollutants near ground level, intensifying their concentration. February and March are typically the worst months for air quality due to the culmination of dry conditions and agricultural activities like burning for land preparation. Sensitive groups – children, the elderly, and those with pre-existing respiratory conditions – should limit strenuous outdoor activity during these months. Monitoring wind direction is crucial; winds from agricultural areas can carry smoke and dust into the city. Staying indoors with windows closed during peak pollution periods is advised.