Reductions in nitrogen oxides over Europe driven by environmental policy and economic recession.

Fuel combustion is a significant source of numerous air pollutants, which reduce local air quality, and affect global tropospheric chemistry. Satellite observations of nitrogen dioxide, emitted by combustion processes, allow for robust monitoring of atmospheric concentrations at high spatial resolution on continental scales. Here we evaluate changes in tropospheric NO(2) concentrations over Europe between 2004 and 2010. We isolate long-term (timescales greater than one year) variability in the daily NO(2) observations from the Ozone Monitoring Instrument (OMI) using a spectral analysis. In 2010, we find substantial reductions in NO(2) concentrations of at least 20% throughout Europe. These reductions are as much the result of temporary reductions prompted by the 2008-2009 global economic recession, as of European NO(x) emission controls. Our results demonstrate that realistic concentration pathways of NO(2) do not follow simple linear trends, but reflect a compilation of environmental policy and economic activity.