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Formosa do Rio Preto, nestled in the heart of Bahia, Brazil, occupies a geographically significant position within the semi-arid Northeast region. Located at approximately -11.0478° latitude and -45.1928° longitude, the city’s terrain is characterized by undulating plains and gently sloping hills, typical of the Cerrado biome. The surrounding landscape is a mosaic of *caatinga* vegetation – thorny shrubs, cacti, and drought-resistant trees – interspersed with patches of gallery forest along the Rio Preto, the river from which the city derives its name. This river, though vital, experiences seasonal fluctuations in flow, impacting local humidity and potentially influencing atmospheric stability. Formosa do Rio Preto’s elevation, relatively low, contributes to a tendency for temperature inversions, particularly during the drier months. The urban footprint is small, reflecting the city’s modest population of just under 26,000. The urban–rural gradient is gradual, with agricultural activities – primarily subsistence farming and livestock grazing – dominating the immediate periphery. While not directly adjacent to major industrial belts, the region experiences agricultural burning practices during land clearing and harvest preparation, a significant contributor to particulate matter. The city’s location within the broader Bahia state, a major agricultural producer, means it is indirectly influenced by regional agricultural activities and transportation networks. The prevailing winds, generally easterly, can transport pollutants from distant sources, though local emissions remain the primary concern. The limited water bodies and relatively flat terrain restrict dispersion of pollutants, potentially exacerbating air quality challenges.

Formosa do Rio Preto’s tropical climate dictates a distinct wet and dry season cycle, profoundly impacting air quality. The dry season, typically spanning from April to September, is characterized by intense solar radiation, low humidity, and infrequent rainfall. This period often witnesses a build-up of particulate matter due to agricultural burning, dust resuspension from dry soils, and reduced atmospheric cleansing. Temperature inversions are more frequent during these months, trapping pollutants near the ground, particularly in the evenings and early mornings. The months of August and September are generally the most challenging for air quality, with increased respiratory irritation reported. Conversely, the wet season (October to March) brings relief through frequent rainfall, which effectively washes pollutants from the atmosphere. Higher humidity also reduces dust resuspension. However, periods of intense rainfall can lead to flooding, potentially releasing mould spores and other allergens into the air. The transition months (March/April and September/October) are often marked by variable conditions, with periods of dust and haze interspersed with rainfall. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activity during peak pollution hours. Maintaining indoor air quality through ventilation and air purification can also be beneficial. During the wet season, while overall air quality improves, vigilance regarding potential allergens is advised. The interplay of wind patterns and rainfall intensity dictates the daily air quality fluctuations, making it crucial to monitor local conditions.