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Urandi, a municipality nestled in the interior of Bahia, Brazil, occupies a geographically complex position within the broader São Francisco River Valley. Located at -14.7708, -42.6550, the city’s terrain is characterised by undulating hills and plateaus, typical of the region’s transitional zone between the semi-arid Sertão and the more humid coastal areas. The surrounding landscape is dominated by *caatinga* vegetation, a thorny scrub forest adapted to prolonged drought, interspersed with areas of cultivated land. Urandi’s elevation, approximately 380 meters above sea level, influences local wind patterns and temperature variations. The city isn’t directly adjacent to large bodies of water, though it lies within the watershed of smaller tributaries feeding the São Francisco. While Urandi isn’t a major industrial hub, agricultural activity, particularly cattle ranching and seasonal crop cultivation, is prevalent in the surrounding areas. This contributes to particulate matter from land use changes and potential burning of vegetation. The urban-rural gradient is relatively sharp, with a concentrated urban core surrounded by extensive agricultural lands. This proximity means that air quality within Urandi is susceptible to pollutants originating from both local sources and regional transport, particularly during drier periods when dust and smoke are easily dispersed. The city’s location within a valley can also trap pollutants, exacerbating air quality issues.

Urandi experiences a distinct wet and dry season, heavily influencing its air quality. The dry season, typically from May to November, presents the most challenging conditions. Reduced rainfall leads to increased dust resuspension from agricultural lands and unpaved roads, elevating particulate matter concentrations. Lower humidity also inhibits the settling of pollutants. Burning for land clearing and agricultural purposes is more common during this period, contributing significantly to smoke and haze. August and September are often the worst months for respiratory irritation. Conversely, the wet season, from December to April, brings relief. Rainfall effectively washes away particulate matter, and increased humidity suppresses dust. However, even during the wet season, localised pollution can occur from vehicle emissions and small-scale burning. Temperature inversions, common during cooler nights throughout the year, can trap pollutants near ground level, worsening air quality even with rainfall. Sensitive groups – children, the elderly, and individuals with respiratory conditions – should limit strenuous outdoor activity during the dry season, particularly in the late afternoon when pollutant concentrations tend to peak. Monitoring wind direction is also crucial, as pollutants can be transported from distant agricultural fires.