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Granollers, nestled in the heart of Catalonia, Spain, occupies a strategically important position within the Vallès Oriental region, a historically significant industrial and agricultural corridor. Located approximately 33 kilometers northeast of Barcelona, its coordinates (41.6080, 2.2880) place it within a gently sloping valley, bordered by the Serra de Sant Llorenç to the north and the undulating plains of the Catalan Pre-Coastal Range to the south. The city’s elevation averages around 280 meters above sea level, contributing to localized microclimates and influencing air circulation patterns. Granollers sits near the confluence of the Tordera and Congost rivers, providing a vital water source and shaping the surrounding landscape. Historically, the area has been a fertile agricultural zone, with extensive fields of cereals and vegetables still visible in the immediate periphery. The urban fabric of Granollers blends a historic core with modern industrial and residential zones, reflecting its evolution from a market town to a significant regional hub. The proximity to Barcelona’s metropolitan area introduces a complex interplay of urban and rural influences. While the city benefits from Barcelona’s economic dynamism, it also faces challenges related to transportation-related pollution and the potential for industrial emissions from nearby zones. The urban–rural gradient is relatively sharp, with agricultural land quickly giving way to built-up areas, impacting local wind patterns and potentially trapping pollutants under certain meteorological conditions. The Serra de Sant Llorenç acts as a partial barrier, sometimes hindering the dispersion of pollutants, particularly during periods of calm weather.

Granollers experiences a Mediterranean climate, significantly impacting its air quality throughout the year. Spring (March-May) typically sees a gradual improvement in air quality as temperatures rise and winds increase, dispersing accumulated winter pollutants. However, pollen levels are high, impacting those with respiratory sensitivities. Summer (June-August) is generally the cleanest period, with consistent sunshine, strong daytime convection, and frequent breezes sweeping across the Vallès Oriental, effectively diluting pollutants. The dry conditions, however, can exacerbate particulate matter issues if dust storms occur. Autumn (September-November) presents a more complex picture. As temperatures cool, the likelihood of temperature inversions increases, particularly in the mornings, trapping pollutants close to the ground. Agricultural burning, a traditional practice in the surrounding areas, can also contribute to elevated particulate matter levels during this season. Winter (December-February) often witnesses the poorest air quality. Cold, stable air masses, coupled with frequent temperature inversions, lead to pollutant accumulation. Fog, common during these months, further restricts dispersion. The city’s location within a valley can exacerbate these effects. Sensitive groups, including children, the elderly, and individuals with pre-existing respiratory conditions, should limit outdoor activity during periods of stagnant air, particularly in the mornings during autumn and winter. Increased vigilance regarding local air quality reports is advised during these times, and indoor air purification can offer some relief.