Disclosed are means for monitoring the levels of air pollution in urban areas for the purpose of optimizing the conditions of airflow ventilation of buildings according to air pollution levels in their area. The invention supplies data in real time regarding local air pollution levels or relative levels, i.e. current air pollution levels in relation to previous ones. The disclosed system and method makes use of the fluctuations in air pollution levels in order to achieve optimal reduction of air pollution levels inside buildings. The system defines optimal times for ventilation in order to achieve a significant and persisting improvement of indoor air quality, in a routine manner, by using measurements of nondeterministic, continuous and effective fluctuations in air pollution levels at the surroundings of each building, specifically in locations which don't include monitoring stations.