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Alexandria, nestled in the Rio Grande do Norte state of Brazil, occupies a geographically significant position along the eastern seaboard, approximately 110 kilometers south of Natal, the state capital. Its coordinates, -6.4128, -38.0158, place it within a coastal plain characterized by relatively low elevation, rarely exceeding 50 meters above sea level. The surrounding landscape is a mosaic of coastal dunes, stretches of pristine beaches, and the transition zone between the Atlantic Forest biome and the Caatinga drylands. This proximity to the Atlantic Ocean exerts a powerful influence on local weather patterns and, consequently, air quality. The city’s urban character is that of a small, developing municipality, primarily reliant on fishing and nascent tourism. While industrial activity is limited, the surrounding region features agricultural zones dedicated to crops like cassava and beans, and livestock farming, which can contribute to localized emissions, particularly during harvest seasons. The urban–rural gradient is relatively sharp, with the immediate vicinity of Alexandria dominated by residential areas and small businesses, quickly giving way to agricultural land and the natural coastal environment. The prevailing winds, generally easterly, blow onshore, potentially carrying pollutants from inland sources towards the coast. The lack of significant topographic barriers means that pollutants tend to disperse relatively quickly, although stagnant air conditions during certain periods can lead to localized build-ups. The Caatinga’s influence introduces dust events, especially during drier periods, impacting particulate matter concentrations.

Alexandria’s tropical climate dictates a wet and dry seasonal cycle, profoundly influencing its air quality profile. The dry season, typically spanning from August to December, is characterized by reduced rainfall and increased temperatures. This period often sees a rise in particulate matter concentrations due to the prevalence of wind-blown dust from the surrounding Caatinga vegetation and agricultural lands. The lack of rainfall means there's less atmospheric cleansing, and the drier air can exacerbate respiratory issues. Conversely, the wet season, from January to July, brings frequent rainfall and higher humidity, which naturally washes pollutants from the atmosphere and reduces dust levels. However, periods of intense rainfall can occasionally lead to localized flooding, which can temporarily release pollutants trapped in the soil. Temperature inversions, though not as frequent as in colder climates, can occur during the dry season, trapping pollutants near the ground, particularly during calmer nights. The prevailing easterly winds generally disperse pollutants, but their strength and consistency vary seasonally. During the wet season, stronger winds associated with tropical disturbances can provide enhanced ventilation. Sensitive groups, such as children, the elderly, and individuals with pre-existing respiratory conditions, should exercise caution during the dry season, limiting outdoor activities during peak dust events. The months of September and October often experience the highest dust concentrations, while March and April typically offer the best air quality conditions for outdoor pursuits.