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São Félix da Marinha, nestled within the Porto district of Portugal, occupies a unique coastal position that significantly shapes its environmental profile. Located at approximately 41.0339° N, -8.6233° W, the town sits on a gently sloping plateau overlooking the Atlantic Ocean, part of the larger Vila Nova de Gaia municipality. The surrounding landscape is characterized by a blend of agricultural land – primarily vineyards and olive groves – and the rugged, picturesque coastline of the Costa Verde. The proximity to the Douro River, flowing into the Atlantic just south of the city, introduces a complex interplay of maritime and fluvial influences. Elevation is relatively low, rarely exceeding 100 meters above sea level, minimizing the potential for topographic barriers to air movement. While São Félix da Marinha itself is a relatively small urban center, it benefits from its adjacency to the larger industrial and commercial hub of Porto, approximately 15 kilometers to the southeast. This proximity means that while direct industrial emissions within São Félix da Marinha are limited, it can be susceptible to pollutants transported from the Porto metropolitan area. The urban–rural gradient is gradual, with agricultural fields and scattered rural settlements transitioning seamlessly into the town’s residential areas. The prevailing westerly winds, typical of the Portuguese coast, play a crucial role in dispersing pollutants, but can also carry maritime aerosols and, occasionally, pollutants from inland sources. The coastal location also means the town experiences a moderating maritime climate, influencing temperature and humidity levels, which in turn affect the behaviour of atmospheric pollutants.

São Félix da Marinha’s air quality exhibits a distinct seasonal pattern largely dictated by meteorological conditions. Summer (June-August) generally sees the best air quality, driven by consistent westerly winds that effectively ventilate the area, dispersing any potential pollutants. Temperatures are high, but the sea breeze provides a cooling effect and helps maintain good mixing. However, prolonged periods of anticyclonic conditions can lead to stagnant air and localized increases in pollutants, particularly during heatwaves. Autumn (September-November) marks a transition period. While winds remain generally westerly, the frequency of temperature inversions increases, especially during calmer periods. These inversions trap pollutants near the ground, potentially leading to poorer air quality, particularly in the mornings. Winter (December-February) often brings the most challenging conditions. Fog, common along the coast, can significantly reduce visibility and trap pollutants, exacerbating any existing issues. While rainfall helps to cleanse the atmosphere, the reduced wind speeds and frequent inversions can lead to periods of elevated pollution. Spring (March-May) sees a gradual improvement as temperatures rise and wind speeds increase, though occasional incursions of Saharan dust can impact air quality. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should be particularly cautious during autumn and winter mornings, limiting strenuous outdoor activity during periods of fog or stagnant air. During summer, while generally good, prolonged heatwaves warrant caution, especially for those vulnerable to heat stress.