A study of the climatology of ventilation properties of the atmosphere in Buenos Aires city has been carried out. From routinely available observational data, the daytime stability conditions and related ventilation factors and airflow characteristics are obtained and studied. In all cases, the seasonal and annual behaviour is analysed. The frequencies of occurrence of daytime reduced ventilation factors are important, being 55% over the whole year and, respectively, 67% and 44% in the cold and warm periods. The prevailing daytime atmospheric stability conditions are near neutral, slightly unstable and unstable. The most frequent daytime wind directions occur in the north-southeast sector and during the cold period are mainly associated with the smallest ventilation factor ranges. The results obtained suggest that, during the cold season, conditions for elevated air pollution concentrations occur with high probability in the atmosphere of Buenos Aires city.