A model study on changes of European and Swiss particulate matter, ozone and nitrogen deposition between 1990 and 2020 due to the revised Gothenburg protocol

Abstract

Abstract. We report a study of changes in air quality due to emission reductions using the chemical transport model CAMx. The model domain includes all of Europe with a nested domain over Switzerland. The model simulations were performed with emissions for 1990 (the reference year for the Gothenburg Protocol), 2005 (the reference year for the revised Gothenburg Protocol), 2006 (for model validation) and 2020 (the target year for the revised Gothenburg Protocol) using three emission scenarios prepared by IIASA/GAINS. Changes in ozone, particulate matter and nitrogen deposition are the central theme of the study. The modelled relative changes in the annual average PM2.5 concentrations between 1990 and 2005 look reasonable based on various PM10 and PM2.5 observations in the past. The results obtained in this study suggest that annual mean concentrations of PM2.5 decreased by about 20–50% in Europe. Simulations using the baseline scenario (BL 2020) suggest that PM2.5 concentrations in 2020 will be about 30% lower than those in 2005. The largest predicted decrease in PM2.5, based on the MTFR (maximum technically feasible reduction) scenario, was about 60% and was located mainly in the eastern part of Europe. In the case of ozone, both model results and measurements show an increase in the mean ozone mixing ratios between 1990 and 2005. The observations, however, suggest a larger increase, indicating the importance of background ozone levels. Although emission reductions caused a decrease in peak ozone values, average ozone levels in polluted regions increased due to reduced titration with nitric oxide (NO). This caused a change in the frequency distribution of ozone. Model simulations using emission scenarios for 2020 suggest that annual average ozone mixing ratios will continue to increase. Changes in the levels of the damage indicators AOT40 for forests and SOMO35 are reported as well. The model results suggest that nitrogen deposition has decreased by 10–30% in the eastern part of Europe since 1990, while it has increased by about 20% in the Iberian Peninsula. The decrease is mainly due to the deposition of oxidized nitrogen species, whereas deposition of reduced nitrogen compounds increased. In Switzerland, nitrogen deposition is larger in the northern part of the Alps, where ammonia emissions are the highest. Applying the baseline scenario, we found that the deposition of oxidized nitrogen compounds will have decreased by a further 40% by 2020, whereas deposition of reduced species will continue to increase. This will lead to a 10–20% decrease in the total nitrogen deposition in most of the model domain, with a 10% increase in the eastern part of Europe.