Changes of air quality due to the revised Gothenburg protocol: Improvement and challenge remains

We modelled the changes in the European air quality between 2010 and 2020 due to the implementation of the revised Gothenburg Protocol by the chemical transport model CAMx (version 6.50). The emissions in 2020 were projected by using the reference year (2005) emissions and country-specific reduction targets (incl. SO₂, NO_x, NH₃, PM_2.5 and NMVOCs) of the revised Gothenburg Protocol. The same inputs for meteorology, boundary conditions and photolysis rates as in 2010 were used for 2020. The modelled results for 2010 were evaluated by measurements obtained from the European air quality database (AirBase), which indicated good agreements for ozone, SO₂, NO_x and PM_2.5. The reduced emissions lead to a decrease in the average concentrations of PM_2.5, SO₂, and NO_x by 12%, 29% and 26%, respectively, between 2010 and 2020. The highest predicted reduction in country level occurs for SO2 (64%) in Poland, for NO_x in the UK (44%), and for PM_2.5 (28%) in Switzerland. The annual average ozone mixing ratios in southern Europe show a slight decrease, while an increase by up to ~3 ppb is observed in the Benelux countries and UK, as the reduced NO_x emissions decrease the ozone titration. However, the maximum daily 8-hour mean ozone concentrations generally decrease in summer when highest ozone formation occurs. Over the 2278 tested stations covering rural, urban and suburban area, the maximum daily 8-hour mean ozone concentrations in summer (June–July–August) are ~2 ppb lower in 2020 than in 2010. Among the simulated pollutants, the PM_2.5 is identified as a crucial target for future. Although the number of countries having annual PM_2.5 concentration below the World Health Organization (WHO) guidelines (10 μg m^-3) increases from 22 in 2010 to 31 in 2020, the eastern Europe could still have high health risk due to PM_2.5 in 2020.