The space–time variability of the fields of CO, NO2, and O3 concentrations and contents in the troposphere of northwestern Russia is analyzed on the basis of experimental data and the results of numerical modeling. The influence that the St Petersburg emission has on the concentrations and contents of CO, NO2,and O3 in the troposphere is estimated for March 2006. A comparison of the measurements of the total CO content and the tropospheric NO2 content with the results of modeling showed a qualitative and, in come cases, quantitative agreement between the results of calculations and experimental data. When synoptic conditions are determined, the St. Petersburg train can be detected at a distance of more than 300 km, which can affect the atmospheric air quality in adjacent countries.