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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  04 Nov 2020

04 Nov 2020

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This preprint is currently under review for the journal ACP.

A Comparison of Long-term Trends in Observations and Emission Inventories of NOx

Elena Macdonald1,2, Noelia Otero Felipe1, and Tim Butler1,3 Elena Macdonald et al.
  • 1Institute for Advanced Sustainability Studies, Berliner Straße 130, 14467 Potsdam, Germany
  • 2Institute for Environmental Science and Geography, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany
  • 3Institute for Meteorology, Free University of Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany

Abstract. Air pollution is a pressing issue that is associated with adverse effects on human health, ecosystems and climate. Despite many years of effort to improve air quality, nitrogen dioxide (NO2) limit values are still regularly exceeded in Europe, particularly in cities and along streets. This study explores how concentrations of nitrogen oxides (NOx = NO + NO2) in European urban areas have changed over the last decades and how this relates to changes in emissions. To do so, the incremental approach was used, comparing urban increments to total emissions and roadside increments to traffic emissions. In total, nine European cities were assessed. The study revealed that potentially confounding factors like the impact of urban pollution at rural monitoring sites through atmospheric transport are generally negligible for NOx. The approach proves therefore particularly useful for this pollutant. The estimated urban increments all showed downward trends and for the majority of the cities the trends aligned well with the total emissions. However, it was found that factors like a very densely populated surrounding or local emission sources in the rural area such as shipping traffic on inland waterways restrict the application of the approach for some cities. The roadside increments showed an overall very diverse picture in their absolute values and trends and also in their relation to traffic emissions. This variability and the discrepancies between roadside increments and emissions could be attributed to a combination of local influencing factors at the street level and different aspects introducing inaccuracies to the trends of the used emission inventories, including deficient emission factors. Applying the incremental approach was evaluated as useful for long-term pan-European studies but at the same time it was found to be restricted to certain regions and cities due to data availability issues. The results also highlight that using emission inventories for the prediction of future health impacts and compliance with limit values needs to consider the distinct variability in the concentrations across but also within cities.

Elena Macdonald et al.

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Elena Macdonald et al.

Elena Macdonald et al.


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Publications Copernicus
Short summary
NO2 limit values are still regularly exceeded in many European cities despite decreasing emissions. Measurements of NOx concentrations from stations across Europe were systematically analysed to assess long-term changes observed in urban areas. We compared trends in concentration increments to trends in total and traffic emissions to find potential discrepancies. The results can help with evaluating inaccuracies in emission inventories and with improving spatial imbalances in data availability.
NO2 limit values are still regularly exceeded in many European cities despite decreasing...