Global climate change is one of the most important scientific, societal and economic contemporary challenges. Fundamental understanding of the major
processes driving climate change is the key problem which is to be solved not only on a global but also on a regional scale. The accuracy of regional
climate modelling depends on a number of factors. One of these factors is the adequate and comprehensive information on the anthropogenic impact
which is highest in industrial regions and areas with dense population – modern megacities. Megacities are not only “heat islands”, but also
significant sources of emissions of various substances into the atmosphere, including greenhouse and reactive gases. In 2019, the mobile experiment
EMME (Emission Monitoring Mobile Experiment) was conducted within the St. Petersburg agglomeration (Russia) aiming to estimate the emission
intensity of greenhouse (CO2, CH4) and reactive (CO, NOx) gases for St. Petersburg, which is the largest
northern megacity. St. Petersburg State University (Russia), Karlsruhe Institute of Technology (Germany) and the University of Bremen (Germany)
jointly ran this experiment. The core instruments of the campaign were two portable Bruker EM27/SUN Fourier
transform infrared (FTIR) spectrometers which were used for
ground-based remote sensing measurements of the total column amount of CO2, CH4 and CO at upwind and downwind locations on
opposite sides of the city. The NO2 tropospheric column amount was observed along a circular highway around the city by continuous mobile
measurements of scattered solar visible radiation with an OceanOptics HR4000 spectrometer using the differential optical absorption spectroscopy (DOAS) technique. Simultaneously, air samples were
collected in air bags for subsequent laboratory analysis. The air samples were taken at the locations of FTIR observations at the ground level and
also at altitudes of about 100 m when air bags were lifted by a kite (in case of suitable landscape and favourable wind conditions). The
entire campaign consisted of 11 mostly cloudless days of measurements in March–April 2019. Planning of measurements for each day included the
determination of optimal location for FTIR spectrometers based on weather forecasts, combined with the numerical modelling of the pollution transport
in the megacity area. The real-time corrections of the FTIR operation sites were performed depending on the actual evolution of the megacity
NOx plume as detected by the mobile DOAS observations. The estimates of the St. Petersburg emission intensities for the
considered greenhouse and reactive gases were obtained by coupling a box model and the results of the EMME observational campaign using the mass
balance approach. The CO2 emission flux for St. Petersburg as an area source was estimated to be 89 ± 28 ktkm-2yr-1,
which is 2 times higher than the corresponding value in the EDGAR database. The experiment revealed the CH4 emission flux of
135 ± 68 tkm-2yr-1, which is about 1 order of magnitude greater than the value reported by the official inventories of
St. Petersburg emissions (∼ 25 tkm-2yr-1 for 2017). At the same time, for the urban territory of St. Petersburg, both the
EMME experiment and the official inventories for 2017 give similar results for the CO anthropogenic flux
(251 ± 104 tkm-2yr-1 vs. 410 tkm-2yr-1) and for the NOx anthropogenic flux
(66 ± 28 tkm-2yr-1 vs. 69 tkm-2yr-1).
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