Systematic analysis of NO2 long-range transport events in GOME-2 satellite data and MACC-II reanalysis model data

Intercontinental long-range transport (LRT) events of NO2 relocate the effects of air pollution from emission regions to remote, pristine regions. I detect transported plumes in tropospheric NO2 columns measured by the GOME-2 / MetOp-A instrument with a specialized algorithm and trace the plumes to their sources using the HYSPLIT lagrangian transport model. With this algorithm I find 3808 LRT events over the ocean for the period 2007 to 2011. I perform an analogous study on data from MACC-II reanalysis and compare the results from both datasets. LRT events occur frequently in the mid-latitudes, emerging usually from coastal high-emission regions. In the free troposphere, plumes of NO2 can travel for several days to the polar oceanic atmosphere or to other continents. They travel along characteristic routes and originate from both continuous anthropogenic emissions and emission events such as bush fires. Most NO2 LRT events occur during autumn and winter months, when meteorological conditions and emissions are most favorable. The evaluation of meteorological data shows that the observed NO2 LRT is often linked to cyclones passing over an emission region. The total transported NO2 content is several permil of the total estimated emission. Results from GOME-2 and MACC-II agree on the Northern Hemisphere while MACC-II produces significantly less transport on the Southern Hemisphere.