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Aiud, nestled in the heart of Alba County, Romania, occupies a geographically significant position within the Transylvanian Basin. Its coordinates (46.3122, 23.7292) place it amidst rolling hills and valleys, a landscape sculpted by glacial activity during the Pleistocene epoch. The city sits at an elevation of approximately 380 meters (1,247 feet) above sea level, contributing to a generally cooler climate compared to lower-lying regions. Aiud’s terrain is characterized by gentle slopes and alluvial plains, a result of the Mureș River and its tributaries shaping the surrounding area. This riverine influence, while providing a water source, also presents a potential pathway for pollutants to disperse. The urban fabric of Aiud is relatively compact, reflecting its historical development as a mining and industrial center. While the city has expanded, a distinct urban–rural gradient is evident, with agricultural lands and forested areas bordering the built environment. The surrounding landscape is predominantly agricultural, with fields of wheat, corn, and rapeseed dominating the views. Further afield, the Apuseni Mountains rise dramatically, influencing regional weather patterns and potentially trapping pollutants under certain atmospheric conditions. Historically, Aiud’s industrial base, particularly its mining operations, has impacted the local environment. While these industries have declined, legacy contamination and ongoing industrial activity in nearby areas can contribute to localized air quality challenges. The basin setting, combined with the surrounding topography, can lead to stagnant air conditions, especially during periods of low wind speed, exacerbating pollution episodes.

Aiud’s air quality experiences a distinct seasonal cycle, largely dictated by meteorological conditions. Winter (December-February) typically presents the most challenging period. Cold temperatures frequently lead to temperature inversions, where a layer of warm air traps cooler air near the ground, preventing pollutants from dispersing. This, coupled with reduced sunlight hours and increased residential heating (often reliant on coal or wood), results in elevated particulate matter concentrations. Fog, common during these months, further compounds the problem by trapping pollutants close to the ground. Spring (March-May) brings a gradual improvement as temperatures rise and wind speeds increase, aiding in pollutant dispersion. However, agricultural activities, such as fertilizer application, can introduce ammonia into the air. Summer (June-August) generally offers the best air quality, with warm temperatures, frequent rainfall, and consistent winds. However, occasional heatwaves can lead to ozone formation, a secondary pollutant. Autumn (September-November) sees a transition period, with decreasing temperatures and increasing humidity. Stubble burning after harvest, a common agricultural practice, can significantly degrade air quality during this time. Sensitive groups, including children, the elderly, and individuals with respiratory conditions, should exercise caution during winter months, limiting outdoor exposure and avoiding strenuous activity on days with poor visibility. During the agricultural seasons, particularly in autumn, those with sensitivities should monitor local air quality reports and consider wearing masks when outdoors.