The concentration of atmospheric pollutants depends on polluting sources, among which transportation is an important contributor. In this paper, pollution caused by the steadily increasing number of road vehicles in Bucharest is studied. The number of imported second-hand cars has increased after 2007, when Romania joined the European Union, compared to the previous period. The effect of the increasing number of road vehicles on the air quality, mainly on the concentration of some air pollutants, as NOx and CO, was investigated for the period 2007-2010. The study was performed for the largest city in Romania, Bucharest, a city with a large number of vehicles. The analysis was made in the economic context taking into account several environmental policies and measures applied by the national and local authorities.