Estimates of CO2 Emissions and Uptake by the Water Surface near St. Petersburg Megalopolis

Using the SOCOM shipboard measurements during March and April 2019, the CO2 emissions and uptake by the water surface of the Gulf of Finland are estimated to determine the possible effect of the water surface on estimates of St. Petersburg’s anthropogenic emissions. The surface of the Gulf of Finland was found to be a CO2 source in March and a CO2 sink in April 2019. The specific CO2 emissions/uptake by the water surface of the Gulf of Finland were, on the average, significantly (1–2 orders of magnitude) smaller than the anthropogenic emissions of St. Petersburg. The contribution of the Gulf of Finland surface to CO2 content in air masses passing over the gulf in March–April 2019 turned out, on average, to be minor as compared to the contribution of St. Petersburg (less than 1% of the city’s contribution) according Emission Monitoring Mobile Experiment (EMME) measurements and Open-Data Inventory for Anthropogenic Carbon dioxide (ODIAC) emission data. For extreme wind speeds over the water surface and differences in the partial CO2 pressure between water and air, the contribution of the Gulf of Finland to the CO2 content in the air masses can reach almost 3% of the anthropogenic contribution of St. Petersburg.