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Penedo, nestled in the state of Alagoas, Brazil, occupies a unique geographic position along the São Francisco River. Located at approximately -10.2900 latitude and -36.5858 longitude, the city’s terrain is characterised by a gentle transition from the coastal plains inland, with a low elevation that contributes to humidity and limited natural air dispersion. The surrounding landscape is dominated by the semi-arid *sertão* vegetation, interspersed with pockets of riverine forest along the São Francisco. Penedo’s urban character is defined by its historical importance as a river port, influencing its layout and economic activities. The city serves as a regional hub for trade and services, connecting the interior of Alagoas and Sergipe states. While not heavily industrialised, agricultural activities, particularly sugarcane and fruit cultivation, are prevalent in the surrounding areas, potentially contributing to particulate matter from land preparation and harvesting. The urban-rural gradient is relatively sharp, with agricultural land immediately bordering the city limits. The proximity to the São Francisco River, while vital for water supply and transport, can also trap pollutants during periods of low flow and atmospheric stability, impacting local air quality. The river’s influence on humidity also affects pollutant dispersion.

Penedo experiences a distinct wet and dry season, heavily influencing its air quality. The wet season, typically from April to August, brings increased rainfall which effectively scrubs the atmosphere, leading to generally improved air quality. However, high humidity can also promote the formation of mould and allergens, impacting respiratory health. The dry season, spanning September to March, presents the greatest air quality challenges. Reduced rainfall allows particulate matter from agricultural activities – sugarcane burning and land clearing – and dust from unpaved roads to accumulate. Temperature inversions are common during the cooler, drier months (June-August), trapping pollutants near ground level. Wind patterns, generally easterly trade winds, can occasionally shift, bringing dust from further inland. November and December are typically the months with the poorest air quality due to the peak of the dry season and agricultural practices. Sensitive groups, including children, the elderly, and those with pre-existing respiratory conditions, should limit strenuous outdoor activity during these periods. Monitoring local conditions and staying indoors on particularly dusty days is advisable. The transition months (March/April and September/October) offer the most favourable conditions for outdoor activities.