Top-Down NO(X) Emissions of European Cities Based on the Downwind Plume of Modelled and Space-Borne Tropospheric NO(2) Columns

Top-down estimates of surface NO(X) emissions were derived for 23 European cities based on the downwind plume decay of tropospheric nitrogen dioxide (NO(2)) columns from the LOTOS-EUROS (Long Term Ozone Simulation-European Ozone Simulation) chemistry transport model (CTM) and from Ozone Monitoring Instrument (OMI) satellite retrievals, averaged for the summertime period (April–September) during 2013. Here we show that the top-down NO(X) emissions derived from LOTOS-EUROS for European urban areas agree well with the bottom-up NO(X) emissions from the MACC-III inventory data (R(2) = 0.88) driving the CTM demonstrating the potential of this method. OMI top-down NO(X) emissions over the 23 European cities are generally lower compared with the MACC-III emissions and their correlation is slightly lower (R(2) = 0.79). The uncertainty on the derived NO(2) lifetimes and NO(X) emissions are on average ~55% for OMI and ~63% for LOTOS-EUROS data. The downwind NO(2) plume method applied on both LOTOS-EUROS and OMI tropospheric NO(2) columns allows to estimate NO(X) emissions from urban areas, demonstrating that this is a useful method for real-time updates of urban NO(X) emissions with reasonable accuracy.