Accurate assessment of air quality on a regional scale and understanding the contribution of various sources is critical for developing mitigation strategies to improve air quality and protect human health. This study is a first attempt to use air quality modeling in characterizing the impact of anthropogenic emissions from urban sources in Russia on air pollution in Northern Europe. We used CMAQ to simulate concentrations of key air pollutants (CO, NO2, O3 and PM) in winter-spring of 2006. We used WRF to simulate meteorology, and SMOKE to prepare emission inputs using the official emission inventory for Russian Federation. CMAQ results were compared with the NO2 ground-based measurements of NO2, CO and O3 at Saint-Petersburg and its suburbs. We found that Saint-Petersburg is the most significant factor impacting air quality in the North-Western region of Russia. Specifically, concentrations of NO2 and CO within the lower layer in the troposphere may exceed background concentrations by 20 and 6 times (corresp