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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 Medvednica mountain range to the north and the Sava River to the south. This geographic setting profoundly influences its air quality dynamics. The city's elevation averages around 120 meters above sea level, with Medvednica rising to 1,035 meters, creating a natural barrier that can trap pollutants under certain meteorological conditions. Zagreb's urban character blends historic Upper Town districts with sprawling lower suburbs, creating an urban-rural gradient where pollution sources vary from dense vehicle traffic in the centre to residential heating in peripheral areas. The Sava River valley acts as a corridor for air masses, but during calm weather, the basin-like topography fosters temperature inversions that concentrate emissions from road transport, industrial zones in the eastern suburbs, and seasonal agricultural burning in surrounding farmlands. Proximity to agricultural regions in Zagreb County introduces particulate matter from field burning, while construction dust from ongoing urban development adds to the mix. The city's location in continental Europe, away from major coastlines, means it lacks the cleansing sea breezes that benefit coastal cities, making it particularly vulnerable to pollution accumulation during stagnant atmospheric conditions.

Zagreb's air quality follows a distinct seasonal pattern shaped by its humid subtropical climate with continental influences. In winter, particularly from November through February, pollution peaks dramatically due to a combination of residential heating with solid fuels, increased vehicle emissions in cold weather, and frequent temperature inversions that trap pollutants near the ground. These inversions occur when cold, dense air settles in the Sava River valley, capped by warmer air aloft, preventing vertical dispersion. Sensitive groups should limit outdoor exertion during these months, especially on calm, foggy days. Spring brings gradual improvement as heating demands decrease and increased precipitation helps wash pollutants from the atmosphere, though construction activities and road dust resuspension can cause temporary spikes. Summer offers the cleanest air, with warmer temperatures reducing heating needs, more frequent winds aiding dispersion, and vegetation absorbing some pollutants; this is the optimal season for outdoor activities. Autumn sees a return to deteriorating conditions as temperatures drop, heating systems activate, and atmospheric stability increases, with October often marking the transition toward winter pollution episodes. Throughout the year, wind patterns from the northwest can provide ventilation, while southeasterly flows may transport additional pollutants from industrial areas.