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Campo Maior, nestled in the interior of Piauí state, Brazil, occupies a unique geographic position within the semi-arid Sertão region. Located at -4.8278 latitude and -42.1686 longitude, the city sits on a relatively flat plateau, averaging around 800 meters in elevation. This plateau is part of the larger Parnaíba River Basin, though Campo Maior itself isn’t directly adjacent to the river; it’s situated inland, influenced by the basin’s broader climatic patterns. The surrounding landscape is characterised by *caatinga* vegetation – thorny scrubland adapted to prolonged drought. The urban character is typical of a regional Brazilian hub, with a central historic district radiating outwards into more modern residential areas. Agriculture, primarily subsistence farming and livestock raising, dominates the surrounding rural areas, with some expansion of commercial agriculture focused on cashew and fruits. The urban-rural gradient is fairly sharp, with a noticeable increase in dust and particulate matter as one moves away from the paved city centre. This proximity to agricultural lands, coupled with the dry climate and flat terrain, contributes to potential air quality challenges, particularly concerning windblown dust and seasonal burning practices. The lack of significant industrial belts within the immediate vicinity means that the primary pollution sources are largely localised and related to transport and agricultural activity.

Campo Maior experiences a pronounced wet and dry season, dictating the rhythm of air quality throughout the year. The dry season, typically from June to November, is when air quality is most compromised. Low rainfall and strong, consistent winds exacerbate dust resuspension from agricultural lands and unpaved roads, leading to increased particulate matter concentrations. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, further worsening conditions. December to May brings the wet season, offering significant relief. Rainfall effectively suppresses dust, and increased humidity helps to settle particulate matter. However, even during the wet season, localised pollution from vehicle emissions and small-scale burning for land clearing can occur. February and March, during peak rainfall, generally represent the best months for outdoor activity. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor exertion during the dry season, particularly August and September. Monitoring local fire reports is crucial, as even distant burns can impact air quality. The transition months (May and November) can be unpredictable, with fluctuating conditions.