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Tomar, nestled in the Santarém district of Portugal, occupies a geographically significant position within the country’s central region. The city is situated on rolling hills, approximately 120 meters above sea level, within the broader Tagus River basin. This terrain influences local air circulation patterns, potentially creating pockets of stagnant air, especially during temperature inversions. The surrounding landscape is a mosaic of agricultural lands – primarily vineyards and olive groves – interspersed with forested areas, characteristic of the Portuguese interior. Tomar’s urban character is defined by its historic centre, a UNESCO World Heritage site, and a more modern expansion reflecting 20th and 21st-century growth. While not a major industrial hub, the region supports some light manufacturing and processing related to agriculture. The proximity to the Nabão River, a tributary of the Tagus, introduces a degree of humidity and can affect pollutant dispersion. The urban-rural gradient is relatively sharp, with agricultural areas immediately bordering the city limits. This proximity means agricultural practices, including seasonal burning of vegetation, can contribute to particulate matter concentrations. The city’s location, shielded by hills to the north and east, can limit long-range pollutant transport, but also trap pollutants during calm weather conditions, impacting local air quality.

Tomar experiences a Mediterranean climate, with distinct wet and dry seasons heavily influencing air quality. Winter (December-February) sees increased particulate matter from wood burning for heating, often exacerbated by temperature inversions trapping pollutants in the valley. Calm, damp conditions limit dispersion. Spring (March-May) brings improving conditions as temperatures rise and rainfall washes away accumulated pollutants, though agricultural burning begins to contribute to PM2.5 and PM10. Summer (June-August) is typically the period of best air quality, with strong sunlight and prevailing winds aiding dispersion. However, prolonged drought can lead to increased dust and wildfire risk, impacting air quality regionally. Autumn (September-November) is a transitional period. The harvest season brings increased agricultural activity and associated emissions. Rainfall increases, but temperature inversions can still occur, trapping pollutants. October and November often see a build-up of particulate matter. Sensitive groups – the elderly, children, and those with respiratory conditions – should limit strenuous outdoor activity during winter and autumn. Monitoring wind direction is crucial; winds from the east can carry pollutants from inland agricultural areas. Avoiding peak burning times and staying indoors during inversion conditions are recommended.