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Barra Velha, nestled in the southern Brazilian state of Santa Catarina, occupies a geographically significant position along the Atlantic coast. Its coordinates (-26.6319, -48.6850) place it within a coastal plain characterized by low elevation, rarely exceeding 30 meters above sea level. The city’s name, meaning ‘old bar’ in Portuguese, references the historical shifting sandbar that once separated the mainland from the island of Barra Velha, now largely integrated into the urban fabric. The surrounding landscape is a blend of coastal dunes, lagoons, and fertile agricultural land, primarily dedicated to rice and soy cultivation – a defining feature of the Itapema River basin. This proximity to intensive agriculture introduces potential sources of particulate matter and ammonia into the air, particularly during planting and harvesting seasons. To the west, the Serra do Mar mountain range acts as a partial barrier, influencing prevailing wind patterns and occasionally trapping pollutants. The urban–rural gradient is relatively sharp, with agricultural fields quickly giving way to residential and commercial areas. The city’s location on the coast means it is directly influenced by maritime air masses, bringing humidity and potentially impacting the dispersion of pollutants. The nearby industrial belt centered around Blumenau, approximately 30 kilometers to the north, contributes to regional air quality concerns, with occasional transport of industrial emissions southward. The Itapema River, flowing through the municipality, also plays a role in local microclimates and potential pollutant transport.

Barra Velha’s subtropical climate dictates a distinct seasonal pattern in air quality. The region experiences a pronounced wet season (roughly November to March) and a drier season (April to October). During the wet season, increased rainfall generally helps to cleanse the atmosphere, reducing particulate matter concentrations. However, the high humidity can exacerbate respiratory issues for sensitive individuals. The frequent fog that develops during these months, particularly in the mornings, can trap pollutants close to the ground, leading to localized episodes of reduced visibility and potentially elevated concentrations of certain gases. The drier season, characterized by lower rainfall and higher temperatures, often sees a build-up of pollutants, especially during periods of stagnant air. Temperature inversions, common during the cooler months (June-August), can trap emissions near the surface, worsening air quality. Agricultural activities intensify during the planting and harvesting periods, releasing dust and agricultural chemicals into the atmosphere. The prevailing winds, generally blowing from the west towards the east, can carry pollutants from inland agricultural zones towards the coast. Individuals with asthma, allergies, or other respiratory conditions should exercise caution during the drier months, particularly during periods of stagnant air or fog. Outdoor activities are generally more favorable during the wetter months, although humidity levels should be considered. The transition months (October and April) often present a mix of conditions, requiring vigilance and awareness of local weather patterns.