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Sacavém, nestled within the Lisboa district of Portugal, occupies a geographically significant position on the northern bank of the Tagus River, approximately 10 kilometers northeast of Lisbon's city center. Its coordinates, 38.7944° N, -9.1053° W, place it within a relatively flat alluvial plain, a legacy of the Tagus’s historical deposition patterns. The surrounding landscape is a blend of urban and agricultural elements; to the north lie rolling hills and vineyards characteristic of the Estremadura region, while to the south, the expansive Tagus estuary dominates the view. The river itself plays a crucial role in Sacavém’s microclimate and air quality, often acting as a conduit for wind and influencing pollutant dispersion. Elevation is minimal, rarely exceeding 20 meters above sea level, contributing to potential stagnation of pollutants under certain meteorological conditions. Historically, the area supported agricultural activities, particularly market gardening, though urbanization has significantly altered the land use pattern. The urban–rural gradient is relatively sharp, with Sacavém transitioning from a suburban character to more rural landscapes within a short distance. While not directly adjacent to major industrial belts, its proximity to Lisbon and the wider metropolitan area means it is susceptible to pollutants originating from those sources, transported by prevailing winds. The Tagus acts as a partial barrier, but also a pathway for pollutants, impacting air quality dynamics. The flat terrain limits vertical mixing, potentially exacerbating ground-level pollution episodes.

Sacavém’s air quality experiences a distinct seasonal rhythm dictated by Portugal’s Mediterranean climate. Summers (June-August) are typically hot and dry, characterized by high-pressure systems that suppress rainfall and create stable atmospheric conditions. This often leads to temperature inversions, where a layer of warm air traps cooler air near the ground, hindering vertical mixing and resulting in pollutant accumulation. The lack of wind during these months further exacerbates the issue, allowing pollutants from Lisbon and surrounding areas to linger. Spring (March-May) and Autumn (September-November) generally offer improved air quality due to increased wind speeds and occasional rainfall, which helps to disperse pollutants. However, periods of calm weather can still occur, leading to localized air quality concerns. Winters (December-February) are wetter, with more frequent rainfall and stronger winds, which naturally cleanse the atmosphere. Fog, however, can form during colder, calmer winter nights, trapping pollutants close to the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during summer months, particularly during heatwaves, and be mindful of potential fog events in winter. Outdoor activities are generally more favorable during spring and autumn, but it’s always advisable to monitor local air quality reports and adjust plans accordingly. The agricultural activity in the surrounding areas can also contribute to seasonal particulate matter, particularly during harvest periods, impacting air quality locally.