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Porto de Mós, nestled in the Leiria district of Portugal, occupies a geographically significant position within the Baixa Práia region, a coastal plain transitioning into the more rugged Serra de Aire e Candeeiros Natural Park. Its coordinates (39.6000, -8.8167) place it approximately 40 kilometers north of Lisbon, benefiting from proximity to the capital's infrastructure while retaining a distinct rural character. The town sits at a relatively low elevation, averaging around 20-30 meters above sea level, contributing to a mild maritime climate. The surrounding landscape is a mosaic of rolling hills, agricultural fields (primarily dedicated to cereal crops and vineyards), and patches of dense Mediterranean scrubland, known as *mato*. To the west lies the Atlantic Ocean, influencing local weather patterns and providing a potential pathway for marine aerosols. The Serra de Candeeiros, a karst landscape of limestone hills and caves, lies to the east, impacting drainage patterns and potentially influencing local wind flows. Porto de Mós exhibits a clear urban–rural gradient; the town itself is a compact settlement, while the surrounding area is predominantly agricultural and sparsely populated. While not directly adjacent to major industrial belts, its proximity to Lisbon and the wider Lisbon Metropolitan Area means it can be affected by transboundary pollution. The relatively flat terrain, combined with the coastal location, can sometimes exacerbate the accumulation of pollutants, particularly during periods of stagnant air. The presence of agricultural activity also introduces potential sources of ammonia and particulate matter, impacting local air quality.

Porto de Mós experiences a Mediterranean climate, resulting in distinct seasonal variations that significantly influence air quality. Summers (June-August) are typically hot and dry, characterized by high-pressure systems that lead to atmospheric stability and temperature inversions. These inversions trap pollutants near the ground, potentially increasing concentrations of particulate matter and ozone, especially during periods of intense sunshine which promotes photochemical smog formation. Spring (March-May) and Autumn (September-November) generally offer improved air quality, with more frequent wind patterns dispersing pollutants. However, autumn can also bring episodes of fog, particularly in October and November, which can trap pollutants and reduce visibility. Winters (December-February) are wetter, with rainfall helping to cleanse the atmosphere. However, periods of cold, calm weather can still lead to localized pollution episodes, particularly from residential heating. The agricultural cycle also plays a role; spring planting and autumn harvesting can generate dust and particulate matter. Sensitive groups, such as children, the elderly, and individuals with respiratory conditions, should be particularly cautious during the summer months, limiting strenuous outdoor activity during peak sunshine hours. During periods of fog in autumn, it’s advisable to avoid prolonged exposure to the outdoors. The prevailing winds, generally from the west, tend to bring in cleaner air from the Atlantic, but can also carry pollutants from the Lisbon region. Maintaining awareness of local weather forecasts and air quality reports is crucial for making informed decisions about outdoor activities throughout the year.