Assessing the Sensitivity of the OMI-NO2 Product to Emission Changes across Europe

The advent of satellite data has provided a source of independent information to monitor trends in tropospheric nitrogen dioxide levels. To interpret these trends, one needs to know the sensitivity of the satellite retrieved NO2 column to anthropogenic emissions. We have applied a chemistry transport model to investigate the sensitivity of the modeled NO2 column, sampled at the OMI (Ozone Monitoring Instrument) overpass time and location and weighted by the OMI averaging kernel, to emission sources across Europe. The most important contribution (approximate to 35%) in Western Europe is made by road transport. Off-road transport and industrial combustion each contribute 10%-15% across continental Europe. In Eastern Europe, power plant contributions are of comparable magnitude as those of road transport. To answer the question if the OMI-NO2 trends can be translated directly into emission changes, we assessed the anticipated changes in OMI-NO2 between 2005 and 2020. Although the results indicated that for many countries, it is indeed possible, for medium- and small-sized coastal countries, the contribution of the increasing shipping emissions in adjacent sea areas may mask a significant part of national emission reductions. This study highlights the need for a combined use of models, a priori emission estimates and satellite data to verify emission trends.