The CO$_{2}$ integral emission by the megacity of St Petersburg as quantified from ground-based FTIR measurements combined with dispersion modelling

The anthropogenic impact is a major factor of climate change, which is highest in industrial regions and modern megacities. Megacities are a significant source of emissions of various substances into the atmosphere, including CO$_{2}$ which is the most important anthropogenic greenhouse gas. In 2019 and 2020, the mobile experiment EMME (Emission Monitoring Mobile Experiment) was carried out on the territory of St Petersburg which is the second-largest industrial city in Russia with a population of more than 5 million people. In 2020, several measurement data sets were obtained during the lockdown period caused by the COVID-19 (COronaVIrus Disease of 2019) pandemic. One of the goals of EMME was to evaluate the CO$_{2}$ emission from the St Petersburg agglomeration. Previously, the CO$_{2}$ area flux has been obtained from the data of the EMME-2019 experiment using the mass balance approach. The value of the CO$_{2}$ area flux for St Petersburg has been estimated as being 89±28 kt km$^{-2}$ yr$^{-1}$, which is 3 times higher than the corresponding value reported in the official municipal inventory. The present study is focused on the derivation of the integral CO$_{2}$ emission from St Petersburg by coupling the results of the EMME observational campaigns of 2019 and 2020 and the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectories) model. ... mehrThe ODIAC (Open-Data Inventory for Anthropogenic CO$_{2}$) database is used as the source of the a priori information on the CO$_{2}$ emissions for the territory of St Petersburg. The most important finding of the present study, based on the analysis of two observational campaigns, is a significantly higher CO$_{2}$ emission from the megacity of St Petersburg compared to the data of municipal inventory, i.e. ∼75800±5400 kt yr$^{-1}$ for 2019 and ∼68400±7100 kt yr$^{-1}$ for 2020 versus ∼30 000 kt yr$^{-1}$ reported by official inventory. The comparison of the CO$_{2}$ emissions obtained during the COVID-19 lockdown period in 2020 to the results obtained during the same period of 2019 demonstrated the decrease in emissions of 10 % or 7400 kt yr$^{-1}$.