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Tábua, nestled within the Coimbra district of Portugal, occupies a geographically significant position in the Beiras region. Located at approximately 40.3667° N, -8.0333° W, the municipality sits on a gently sloping terrain, part of the broader Serra do Açor mountain range foothills. This location influences local air circulation patterns. The surrounding landscape is predominantly rural, characterized by a mosaic of agricultural fields – primarily maize, cereals, and vineyards – interspersed with patches of oak woodland and pine forests. This agricultural activity, while vital to the local economy, can contribute to seasonal particulate matter emissions, particularly during harvest periods. Tábua’s elevation, averaging around 350 meters above sea level, contributes to occasional temperature inversions, especially during the cooler months, which can trap pollutants near the ground. The municipality lacks direct proximity to major bodies of water; the nearest significant river, the Mondego, is several kilometers away, limiting the potential for evaporative cooling and pollutant dispersion. While not directly adjacent to major industrial belts, Tábua’s location within the Coimbra region places it within a moderate urban–rural gradient, experiencing some influence from the larger urban center of Coimbra, including occasional transport-related emissions. The prevailing winds generally flow from the west, bringing maritime air, but local topography can disrupt these patterns, creating pockets of stagnant air and localized pollution hotspots. The relatively small population density contributes to a generally lower baseline pollution level compared to larger Portuguese cities.

Tábua’s air quality exhibits a distinct seasonal pattern dictated by Portugal’s Mediterranean climate. Spring (March-May) typically sees improved air quality as temperatures rise and winds increase, dispersing any accumulated winter pollutants. However, agricultural burning, a traditional practice in the region, can occasionally lead to short-term spikes in particulate matter. Summer (June-August) is generally the cleanest period, with consistent sunshine, strong winds, and high temperatures promoting excellent ventilation. The dry conditions, however, can increase the risk of wildfires, which can severely degrade air quality over a wider area. Autumn (September-November) marks a transition period. As temperatures cool, the likelihood of temperature inversions increases, particularly in October and November, trapping pollutants and leading to periods of reduced visibility and potentially poorer air quality. Agricultural activities intensify during harvest, contributing to particulate emissions. Winter (December-February) is often the most challenging season. Cold, stable air masses frequently settle over the region, creating conditions conducive to temperature inversions and stagnant air. Fog, common during these months, further exacerbates the problem by trapping pollutants close to the ground. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should limit prolonged outdoor activity during periods of fog or stagnant air, particularly in the mornings. Increased vigilance regarding wood-burning stoves, a common heating source, is also advised during the colder months to minimize indoor and outdoor pollution.