“…In this situation, the position of air entries and exhausts, together with the amount of recirculated air or amount of fresh air added to the mixture, can be considered as design variables to test different ventilation modes and improve the expulsion of internal emitted aerosols. On the other hand, a second set of studies have simulated in-cabin turbulent flows formed at the expenses of the exterior air flowing through the open windows of the bus, or having no air conditioning system, as happens in many Latin American, Asian and African countries; these papers 8,[16][17][18][19] conform the main background of the present report. First of all, the majority of these studies have revealed a characteristic flow inside urban buses that may not be obvious at first glance: contrary to what we may expect, when a bus is moving at a certain speed having a fixed number of open windows, the exterior air enters from the back windows and then travels towards the front pushing or sweeping the aerosols from back to front, on average.…”