Analysis of Emission-Driven Changes in the Oxidation Capacity of the Atmosphere in Major European Urban Cities

Abstract

Air quality is highly affected by emissions generated by human activities. Anthropogenic emissions in Europe have gradually been reduced thanks to a combination of factors, including restrictive regulation and policy implementation, fuel switching, technological developments, and improved energy efficiencies. Many measures have been specifically introduced to meet the NO2 limit values for the protection of human health, primarily targeting traffic emissions. Due to NOX reduction policies in Europe, NO2 levels have been generally reduced, but O3 concentrations have been found to increase. This phenomenon would cause changes in the oxidant capacity of the atmosphere, promoting the formation of tropospheric oxidants. In order to observe the occurrence in Europe, the Community Multiscale Air Quality Modeling System (CMAQ) is applied in this study. We examine the variation for two months representative of winter and summer conditions (January and July) in the period of 2007–2015. In addition to observing the general situation, we selected 67 European large cities (those with more than 0.5 million inhabitants in 2015) to analyze the trends of pollutants along with NOX emission changes by means of statistical methods. Additionally, we characterized the phenomenon of general changes in the oxidation capacity of the atmosphere dividing into five groups. As a general result, we found that NOX emissions and NO2 concentrations decreased in the period in both seasons. On the other hand, concentrations of O3 and other main tropospheric oxidants (OH and NO3) increased in winter but decreased in summer. However, the OH radical also shows an increase in urban areas in summer. Finally, HNO3 shows a negative trend in general.