Estimates of CO2 anthropogenic emissions of St. Petersburg megacity per 1 km2 and per whole city`s area (integral emissions) which are based on the ground-based measurements of CO2 content on the territory of the city are presented in the study. To obtain emissions, inverse problem was solved using the results of comparison between measured and calculated (ODIAC dataset) city`s anthropogenic contribution to CO2 content. Two approaches were used. In the first a tomography method was implemented to estimate anthropogenic emissions of three city`s regions per 1 km2. In the second all available measurements were used to derive average correcting factor R and to obtain integral CO2 emissions of the megacity and its central part. The emissions per 1 km2 for south of the city are in range 32.7–48.3, for center – 69.0–97.5, for north – 78.2 kt/km2. The integral CO2 emissions from the territories of the megacity and its central part constitute 65.3 and 39.8 Mt/year respectively. Inaccuracies of the estimates are 20–40%. The estimates of the St. Petersburg CO2 anthropogenic emissions are higher approximately in 2 times than earlier results.