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(a) Top-down derived NOX emissions estimated from the tropospheric NO2 line densities for different European cities against scaled Airbase measurements of surface NO2 concentrations. NOX emissions from LOTOS-EUROS versus MACC-III in red. OMI based versus MACC-III in black. No surface data available for St.-Petersburg, Moscow and Kiev. (b) The distribution of the difference of the top-down and surface based observed emissions.
