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Nestled in the South Moravian Region of the Czech Republic, Brno occupies a strategic position at the confluence of the Svratka and Svitava rivers, approximately 200 kilometres southeast of Prague. As the country's second-largest city, Brno serves as the cultural and administrative heart of Moravia, characterised by a blend of historic architecture and modern urban development. The city lies within the Dyje-Svratka Valley, surrounded by the Bohemian-Moravian Highlands to the west and the Carpathian foothills to the east, creating a basin-like topography that significantly influences air quality. At an elevation of around 190–250 metres above sea level, Brno's terrain features gentle hills and river valleys, which can trap pollutants under stable atmospheric conditions. The urban area transitions into agricultural zones and vineyards in the surrounding countryside, part of the fertile South Moravian region. Proximity to the Czech-Moravian industrial corridor, stretching from Ostrava through Brno to Vienna, introduces emissions from manufacturing and energy production. The city's location in a valley exacerbates pollution accumulation, particularly during temperature inversions common in winter, when cold air settles in the basin, preventing the dispersion of vehicle exhaust, industrial emissions, and particulate matter from residential heating and road dust. This geographic setting, combined with Brno's role as a major transport hub, creates persistent air quality challenges, especially in the urban core.

Brno's air quality follows a distinct seasonal pattern shaped by its humid continental climate, with pollution levels peaking dramatically during the colder months. In winter, from November through February, temperature inversions frequently occur as cold, dense air settles in the city's valley basin, trapping pollutants from vehicle exhaust, industrial emissions, and residential heating—often reliant on solid fuels. This stagnation leads to elevated concentrations of particulate matter (PM2.5 and PM10) and nitrogen oxides, making these months the least favourable for outdoor activities, especially for sensitive groups like children, the elderly, and those with respiratory conditions. Spring brings gradual improvement as increased solar radiation and more frequent winds help disperse pollutants, though construction dust and road dust stirred by thawing conditions can cause temporary spikes. Summer offers the cleanest air, with longer daylight hours, higher temperatures, and convective winds promoting better mixing, although heatwaves can occasionally lead to ozone formation from vehicle emissions. Autumn sees a return to deteriorating conditions as temperatures drop and atmospheric stability increases, with October often marking the onset of pollution buildup. Sensitive individuals should monitor air quality forecasts year-round, limit strenuous outdoor exercise during winter inversions, and consider using air purifiers indoors when pollution is high.