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Várzea Nova, nestled in the interior of Bahia state, Brazil, occupies a geographically significant position within the semi-arid Sertão region. Located at -11.2589 latitude and -40.9419 longitude, the city sits on a relatively flat terrain, typical of the vast plains characteristic of this part of Brazil. The surrounding landscape is dominated by *caatinga* vegetation – a unique, drought-resistant scrubland – interspersed with areas dedicated to agriculture, primarily subsistence farming and, increasingly, larger-scale production of crops like beans and corn. The city’s elevation is modest, contributing to limited natural dispersion of pollutants. While not directly adjacent to a major body of water, Várzea Nova is influenced by seasonal river flows and the broader hydrological cycle of the São Francisco River basin, some distance away. The urban-rural gradient is pronounced; the city centre represents a concentrated area of activity, while the periphery quickly transitions into agricultural lands. This proximity to agricultural practices, including potential burning for land clearing, significantly impacts local air quality. The lack of substantial industrial belts within Várzea Nova itself means that the primary pollution sources are linked to transportation, domestic fuel burning, and agricultural activities. Dust from unpaved roads and agricultural fields is also a major contributor to particulate matter.

Várzea Nova experiences a distinct wet and dry season, heavily influencing its air quality. The dry season, typically from August to December, 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. Temperature inversions, common during the cooler nights of the dry season, trap pollutants near the ground, exacerbating air quality issues. January to April marks the wet season, bringing significant improvements. Rainfall effectively washes away particulate matter, and increased humidity promotes pollutant dispersion. However, even during the wet season, localized pollution can occur due to ongoing agricultural activities. May to July represents a transitional period with fluctuating conditions. Sensitive individuals – children, the elderly, and those with respiratory conditions – should be particularly cautious during the dry season, limiting strenuous outdoor activity and monitoring their health. The months of February and March, coinciding with peak rainfall, generally offer the most favourable air quality for outdoor pursuits. Burning for agricultural purposes, even if illegal, is a key driver of seasonal peaks, often occurring before the rains begin.