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Olhão, nestled in the heart of the Algarve region of Portugal, occupies a unique geographic position profoundly influencing its air quality. Situated on the Ria Formosa Natural Park, a lagoon system of islands and channels, the city benefits from a coastal location with a relatively flat terrain, averaging just 10 meters above sea level. This low elevation, combined with the surrounding waters, generally promotes sea breezes that can disperse pollutants, but also creates conditions conducive to temperature inversions under certain meteorological circumstances. Olhão’s urban character is distinctly maritime, with a historic fishing port at its core, and a sprawling residential area extending inland. The surrounding landscape is a mosaic of salt pans, agricultural fields (primarily citrus groves and market gardens), and pristine beaches. To the north, the landscape gradually rises towards the Serra do Caldeirão mountain range, which can occasionally trap pollutants. The urban–rural gradient is relatively sharp, with agricultural activity occurring within a few kilometers of the city center. While Olhão itself lacks significant heavy industry, it’s part of a broader Algarve region experiencing tourism-related growth, and the proximity to industrial zones further east along the coast, though distant, can contribute to transboundary pollution events. The prevailing winds, typically from the west and southwest, play a crucial role in both bringing in marine air and potentially transporting pollutants from other areas.

Olhão’s air quality exhibits a distinct seasonal pattern dictated by the region’s Mediterranean climate. Summers (June-August) are typically characterized by high temperatures and prolonged periods of sunshine, often accompanied by light, stable winds. This can lead to the formation of temperature inversions, particularly during the early morning hours, trapping pollutants close to the ground. While the sea breeze usually provides some relief, stagnant air periods can occur, potentially impacting sensitive individuals. Spring (March-May) and Autumn (September-November) generally offer the most favourable air quality, with more frequent and stronger winds dispersing pollutants. Winter (December-February) brings cooler temperatures and increased rainfall, which helps to cleanse the atmosphere. However, occasional cold fronts can bring in pollutants from northern regions. Fog, more common during the winter months, can also exacerbate air quality issues by trapping pollutants. The agricultural activity surrounding Olhão, particularly the use of machinery and fertilizers, contributes to localized pollution episodes, especially during planting and harvesting seasons. Individuals with respiratory conditions, the elderly, and young children should be particularly mindful of air quality forecasts during the summer months and on days with stagnant air. During periods of agricultural activity, minimizing exposure near fields is advisable. Overall, the shoulder seasons of spring and autumn provide the most consistently clean air for outdoor activities.