Aratuba, Ceará, Brazil, nestled within the northeastern Brazilian hinterland, presents a compelling case study in how geography shapes urban air quality. Located at approximately -4.4178° latitude and -39.0450° longitude, the city sits on a relatively flat terrain, characteristic of the Sertão biome. This region is predominantly semi-arid, with sparse vegetation and limited surface water, although the nearby Rio Salgado provides a crucial, albeit seasonal, water source. Aratuba’s position within the larger Fortaleza metropolitan area, though not directly adjacent, places it within the sphere of influence of regional industrial and agricultural activities. The urban–rural gradient transitions rapidly, with small-scale agriculture (primarily subsistence farming and livestock rearing) dominating the surrounding landscape. The soil composition, often sandy and nutrient-poor, contributes to dust generation, a significant factor in local air quality. The elevation is low, averaging around 150 meters above sea level, which can exacerbate temperature inversions, particularly during the dry season. While Aratuba itself is a smaller municipality, its proximity to larger population centers and agricultural zones means it’s susceptible to pollutants transported from elsewhere. The prevailing winds, generally easterly, can carry dust and emissions from agricultural burning practices common in the region, impacting air quality even in this relatively isolated locale. The lack of significant topographic barriers further limits natural air purification processes.

Aratuba’s tropical climate dictates a distinct wet and dry season cycle, profoundly influencing its air quality profile. The dry season, typically spanning from August to May, is characterized by intense solar radiation, high temperatures, and minimal rainfall. This period often witnesses a significant increase in particulate matter due to windblown dust from the surrounding Sertão landscape. Agricultural burning, a traditional land management practice, intensifies during this time, releasing substantial amounts of smoke and pollutants into the atmosphere. Temperature inversions are more frequent during the dry season, trapping pollutants near the ground, particularly in the early morning hours. The wet season, from May to August, brings relief with increased rainfall, which naturally washes away particulate matter and helps to disperse pollutants. However, heavy rainfall can also lead to increased humidity and the formation of ground-level ozone, especially during periods of intense sunshine. The prevailing easterly winds play a crucial role, often carrying dust and smoke from agricultural areas to the west and northwest, impacting Aratuba’s air quality. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak dust and smoke periods. During the wet season, while overall air quality improves, those with sensitivities to humidity or ozone should monitor conditions and take appropriate precautions. The months of September through November often present the most challenging air quality conditions due to a combination of agricultural burning and persistent dry conditions.