Impact of primary NO2 emissions at different urban sites exceeding the European NO2 standard limit

Abstract A large part of the European population is still exposed to ambient nitrogen dioxide (NO 2 ) levels exceeding the European Union (EU) air quality standards, being a key challenge to reduce NO 2 concentrations across many European urban areas, particularly close to roads. In this work, a trend analysis of pollutants involved in NO 2 processes was done for the period 2003–2014 in traffic sites from three Spanish cities (Barcelona, Madrid and Granada) that still exceed the European NO 2 air quality standard limits. We also estimated the contributions of primary NO 2 emissions and photo-chemically formed NO 2 to the observed ambient NO 2 concentrations in order to explore their possible role in the observed NO 2 concentration trends. The NO x and NO concentrations at these traffic sites showed significant decreasing trends during the period 2003–2014, especially at Barcelona (BAR TR ) and Madrid (MAD TR ) traffic stations. The NO 2 concentrations showed statistically significant downward trends at BAR TR and MAD TR and remained unchanged at Granada traffic station (GRA TR ) during the study period. Despite the significant decrease in NO 2 concentrations in BCN TR and MAD TR during the analysed period, the NO 2 concentrations observed over these sites still above the annual NO 2 standard limit of 40 μg m −3 and, therefore, more efficient measures are still needed. Primary NO 2 emissions significantly influence NO 2 concentrations at the three analysed sites. However, as no drastic changes are expected in the after-exhaust treatment technology that can reduce primary NO 2 emissions to zero in the near future, only a substantial reduction in NO x emissions will help to comply with the NO 2 European air quality standards. Reduction of 78%, 56% and 16% on NO x emissions in Barcelona, Madrid and Granada were estimated to be necessary to comply with the NO 2 annual limit of 40 μg m −3 .