Boninal, nestled in the state of Bahia, Brazil, presents a unique geographic context influencing its air quality. Located at -12.7019° latitude and -41.8278° longitude, the city sits within the semi-arid Sertão region, characterized by a rugged terrain of *chapadas* (plateaus) and *caatinga* (thorn scrubland). The surrounding landscape is predominantly dry forest and scrub, with limited surface water. Boninal’s elevation, while not extreme, contributes to localized weather patterns. The urban area itself is relatively compact, reflecting its population of approximately 13,622. The city’s position isn’t near major industrial belts, a positive factor, but is surrounded by agricultural lands, primarily dedicated to subsistence farming and livestock raising. These agricultural practices, including seasonal burning for land clearing, are a significant source of particulate matter. The urban-rural gradient is sharp; immediately outside the city limits, the landscape transitions rapidly to sparsely populated rural areas. This impacts air dispersion, as pollutants can accumulate more readily within the city basin, especially during periods of calm winds. The lack of significant natural barriers to air flow, combined with the dry climate, means dust and aerosols are easily mobilized, affecting local air quality. The region’s geology, rich in iron and manganese, also contributes to soil dust composition.

Boninal experiences a pronounced wet and dry season, dictating the rhythm of air quality. The dry season, typically from August to December, is when air quality deteriorates most significantly. Reduced rainfall means less atmospheric cleansing, and agricultural burning for preparing fields for planting becomes widespread, releasing substantial amounts of particulate matter (PM2.5 and PM10). Strong, dry winds exacerbate dust resuspension from the *caatinga* vegetation and exposed soils. January to April marks the wet season, bringing relief from dust and smoke. Rainfall washes pollutants from the atmosphere, and vegetation growth suppresses dust emissions. However, even during the wet season, localized flooding can mobilize sediment and contribute to microbial air pollutants. May to July represents a transitional period, with variable rainfall and moderate air quality. Temperature inversions, common during cooler nights throughout the year, can trap pollutants near ground level, worsening conditions. Sensitive individuals – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during the peak of the dry season (September-November). Fog, while not frequent, can also trap pollutants during cooler mornings. Monitoring wind direction is crucial; winds from agricultural areas will likely carry smoke and dust into the city.