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São Pedro do Sul, nestled in the Viseu District of Portugal, occupies a geographically significant position within the Dão region. Its coordinates (40.7500, -8.0667) place it within a gently undulating landscape, characterized by rolling hills and valleys typical of the Portuguese interior. The town sits at an elevation of approximately 480 meters (1,575 feet) above sea level, contributing to a cooler climate compared to coastal areas. The surrounding landscape is predominantly rural, a mosaic of vineyards, olive groves, and traditional agricultural fields, reflecting the region’s strong agricultural heritage. The Serra da Estrela, Portugal’s highest mountain range, lies to the northeast, influencing regional weather patterns and occasionally contributing to localized wind flows. While São Pedro do Sul lacks direct proximity to major rivers or large bodies of water, it benefits from several smaller streams and springs, historically vital for the town’s development and thermal baths. The urban fabric is relatively compact, exhibiting a gradual urban–rural gradient as one moves outwards. There are no major industrial belts immediately adjacent to São Pedro do Sul; however, the broader Viseu region supports some light industry and agricultural processing, which could contribute to localized air pollution episodes. The town’s location inland, shielded by surrounding hills, can sometimes trap pollutants, particularly during periods of atmospheric stability. The prevailing winds generally flow from the west, bringing air masses from the Atlantic, but local topography can significantly alter these patterns, creating microclimates and influencing air quality variations.

São Pedro do Sul experiences a temperate climate with distinct seasonal variations that significantly impact air quality. Spring (March-May) typically brings a gradual improvement in air quality as temperatures rise and vegetation begins to flourish, absorbing some pollutants. However, pollen levels can increase, affecting individuals with allergies. Summer (June-August) is generally characterized by drier conditions and higher temperatures, which can exacerbate ozone formation, a secondary pollutant. Stagnant air masses during heatwaves can trap pollutants, leading to localized episodes of reduced air quality. Autumn (September-November) often sees a return to more favorable conditions, with increased rainfall helping to cleanse the atmosphere. However, agricultural burning, a traditional practice in the region, can contribute to particulate matter pollution during this period. Winter (December-February) is often the most challenging season for air quality. Cold, stable air masses frequently lead to temperature inversions, where a layer of warm air sits above cooler air near the ground, preventing pollutants from dispersing. Fog, common during winter mornings, further traps pollutants. The combination of reduced sunlight, lower temperatures, and stagnant air can result in elevated levels of particulate matter and other pollutants. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit outdoor activity during periods of fog or temperature inversions, particularly in the early morning. Increased ventilation in homes is also advisable during these times.