In this work we present the first and longest zenith-sky mobile DOAS (Differential Optical Absorption Spectroscopy) measurements performed in Southeast Europe. The mobile DOAS observations were performed on board of a motor vehicle using an UV-Vis spectrometer during several days on 2015 and 2016 in Romania, Bulgaria, Greece and Republic of Moldova. The target trace gases are: nitrogen dioxide (NO2) and sulfur dioxide (SO2). The mobile DOAS measurements performed on ground represents aproximative 1500km travelled on roads. The highest tropospheric NO2 (1x1017 molec./cm2) and SO2 (~2.5x1018 molec/cm2) content was determined in the Jiu Valley Romania, where large fossil-fuel power station exist. The study also presents comparisons of tropospheric NO2 Vertical Column Density (VCD) deduced from mobile DOAS measurements with Ozone Monitoring Instrument observations. We found a good agreement between ground and space observations for two important urban agglomerations. For Bucuresti city the averaged mobile DOAS observations function of OMI pixel coordinates show 4.11 (±0.61) x1015 molec/cm2 while OMI detected 5.94 (±2.87) x1015 molec/cm2. For the other important city, Thessaloniki, averaged mobile DOAS observations indicate 5.44 ± (0.84) x1015 molec/cm2while OMI space observations presents 5.66 (±1.56) x1015 molec/cm2. We found also that due to the smoothing effect inside the pixel, OMI sensor underestimated the important NO2 emissions located in the Jiu Valley, Romania.