air quality; climate change; model study; emission
Air quality is strongly dependent on meteorology and thus is sensitive to climate change. In order to study the impact of a changing climate on particulate matter (PM) concentration over Europe and on the PM urban increment of three north-west European urban agglomerations two different model approaches have been used in this study. Another focus was on the strengths and weaknesses of the model systems used in the approaches. The first approach was to analyze a synoptic situation in the past which is expected to occur more often in the future, here the extreme meteorological situation in the summer 2003, in terms of its effect on the concentration of PM10 and its components. To this end measurements and model simulations with the chemistry transport models (CTMs) LOTOS-EUROS and REM/Calgrid of the summer 2003 were compared to the summer average of the years 2003-2007. The second approach was to use the off-line coupled model system RACMO2 (regional climate model) – LOTOS-EUROS (air quality model) over Europe. Three different sets of simulations were carried out using RACMO2 meteorology with boundary conditions from two different global climate models (scenario runs) and from reanalysis data. Motivated by findings of the first studies the sensitivity of air pollutant simulations with the LOTOS-EUROS model to temporal distribution of anthropogenic emissions using more detailed time profiles for three source categories were tested.
PM10 concentrations in Europe may be affected by climate change, as indicated by the observed positive differences in PM10 concentrations between the extreme summer of 2003 and the five years summer average. The investigation of the impact of climate change on air quality with a numerical model system requires a good description of the processes related to meteorology in the CTMs. One main outcome is that both CTMs failed to fully reproduce the increase of measured PM10 concentrations during conditions with very low and high daily maximum temperature and also underestimate the increased concentrations in the summer 2003. This was found to be mainly due to missing but important components and emission sources or uncertainties therein. Furthermore, a dependency of anthropogenic emission on meteorology is not considered in the models but may enhance the model performance as indicated by results of the sensitivity study. The impact of climate change on the simulated PM10 concentrations and the urban increment was found to be small in both scenario runs performed with the RACMO2 – LOTOS-EUROS model system. For many locations the two climate runs did not agree on the sign of the changes. The meteorological parameters from both RACMO2 climate simulations differ considerably from those of the reanalysis-driven simulation for a present-day climate period. These differences have a substantial impact on the simulated PM10 concentrations and also affect the urban increment.
Both model approaches presented in this study are useful tools to investigate the impact of a changing climate on PM concentrations but due to considerable weaknesses in the model systems a qualitative rather than a quantitative interpretation of the simulation results is recommendable. An important point when investigating the impact of climate change on air quality with coupled model systems is to enhance the CTM model performance as function of meteorology.
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