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Reus is situated in the heart of the Camp de Tarragona, a fertile coastal plain in Catalonia, Spain. Positioned slightly inland from the Mediterranean coast, it serves as a critical commercial and administrative hub. The terrain is predominantly flat, characterized by low elevation and a gentle slope toward the sea, which fundamentally shapes its atmospheric dynamics. The city is embedded within a rich agricultural mosaic, where vineyards and olive groves dominate the periphery, introducing biogenic emissions and agricultural ammonia into the urban air basin. To the south and east, the proximity to the massive petrochemical complex of Tarragona creates a regional pollution gradient, as industrial plumes can be transported toward Reus depending on wind direction. The urban fabric is dense, with a historic core transitioning into modern residential and expanding industrial sectors, creating a distinct urban-rural gradient. This layout facilitates the accumulation of vehicular emissions from the intersecting high-capacity road networks, including the nearby AP-7 highway, which acts as a constant source of nitrogen oxides and particulates. The lack of significant topographic barriers allows for the influence of sea breezes, which typically help disperse pollutants during the day but can lead to the recirculation of contaminants during nocturnal shifts. Consequently, Reus exists at a crossroads of industrial output, agricultural activity, and transit-heavy infrastructure, making its air quality highly sensitive to the interplay between regional industrial emissions and the local Mediterranean meteorological patterns that govern the movement of air masses across the plain.

Air quality in Reus follows a distinct Mediterranean cycle driven by temperature and wind. In winter, the city often experiences thermal inversions, where cold air traps pollutants—primarily nitrogen dioxide and particulates from heating and traffic—close to the ground. This creates stagnant periods, particularly in December and January, making these months challenging for asthmatics. Spring brings a shift as rising temperatures and increased wind speeds generally clear the air, though this period is marked by high pollen counts and occasional Saharan dust intrusions, which spike particulate matter levels. Summer is the most critical season for ozone formation. Intense solar radiation reacts with precursors from the Tarragona industrial belt and local traffic, leading to photochemical smog. July and August often see peak ozone levels, necessitating caution for children and the elderly during peak afternoon heat. Autumn typically provides the cleanest air, as the arrival of Mediterranean depressions and frequent rainfall effectively "wash" the atmosphere of suspended particles. October and November are ideal for outdoor activities. For sensitive groups, the primary health guidance is to monitor local alerts during summer heatwaves and winter cold snaps. While the sea breeze provides a daily cleansing mechanism, the nocturnal stagnation during winter and the photochemical intensity of summer remain the primary meteorological drivers of pollution. By aligning outdoor exercise with the early morning hours in summer and avoiding peak traffic corridors in winter, residents can significantly mitigate their overall exposure to the city's periodic atmospheric pollutants and the negative health effects associated with them every single day.