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Zagreb, Croatia's capital and largest city, occupies a strategic position at the southwestern edge of the Pannonian Basin, nestled between the southern slopes of Medvednica Mountain to the north and the Sava River to the south. This unique geographic setting creates a distinct urban character where the historic Upper Town (Gornji Grad) perches on elevated terrain, while the modern Lower Town (Donji Grad) spreads across the river's floodplain. The city's location at approximately 120-150 meters above sea level places it in a transitional zone between continental and Mediterranean influences, with Medvednica acting as a natural barrier that can trap pollutants during atmospheric inversions. Zagreb's urban-rural gradient extends eastward into fertile agricultural plains of the Pannonian region, while westward development follows the Sava River valley. The city's air quality is directly impacted by this basin-and-mountain topography, which limits natural ventilation when winds are calm, allowing particulate matter and nitrogen oxides from transportation and residential heating to accumulate. Proximity to the Sava River provides some moderating effects but doesn't significantly disperse pollution during stagnant conditions. The urban core's dense development contrasts with greener northern suburbs climbing Medvednica's slopes, creating microclimatic variations in pollution exposure across the metropolitan area.

Zagreb's air quality follows distinct seasonal patterns shaped by its continental climate with Mediterranean influences. Winter months from December through February typically see the poorest air quality, as temperature inversions become frequent in the basin-like terrain, trapping pollutants from residential wood and coal heating, combined with vehicle emissions. Cold, stagnant conditions with limited wind dispersal create persistent haze, making these months least favourable for outdoor activities, especially for those with respiratory conditions. Spring brings gradual improvement as temperatures rise and precipitation increases, with March and April experiencing better dispersion though occasional Saharan dust episodes can temporarily elevate particulate levels. Summer offers the cleanest air from June through August, with warmer temperatures reducing heating emissions and more frequent southerly winds providing better ventilation, though occasional heatwaves can increase ozone formation. Autumn sees a transitional period where September and October maintain relatively good conditions before November's cooling temperatures and increased heating use begin degrading air quality again. Sensitive groups should limit prolonged outdoor exposure during winter inversion episodes, schedule activities for midday when pollution often temporarily improves, and monitor local air quality indices particularly during calm, cold periods when particulate concentrations peak.