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The aerosol distribution in Europe derived with the Community Multiscale Air Quality (CMAQ) model: comparison to near surface in situ and sunphotometer measurements

In order to assess the air quality over Europe the aerosol distribution was simulated for the years 2000 and 2001. Aerosol particles belong to the most important air pollutants in Europe and they represent one of the largest uncertainties in climate models. The largest aerosol concentrations are found in the Benelux area, in south Poland, the Po valley, Bulgaria and Romania.

The chemical components of the total aerosol that result from anthropogenic activities (which are ammonium, nitrate and sulphate) are better represented than e.g. organic aerosols. They stem from natural sources but also from combustion of organic material like wood. The emissions sources are not yet quantified accurate enough and aerosol formation processes are not yet fully understood.
The total aerosol concentrations are underestimated by 30-60 % in the model. This is also found from optical measurements that include higher atmospheric layers.

Abstract

Abstract (published in Atmospheric Chemistry and Physics, (8, 5077-5097 (2008))):

The aerosol distribution in Europe was simulated with the Community Multiscale Air Quality (CMAQ) model system version 4.5 for the years 2000 and 2001. The results
were compared with daily averages of PM10 measurements taken in the framework of EMEP and with aerosol optical depth (AOD) values measured within AERONET. The modeled total aerosol mass is typically about 30–60% lower than the corresponding measurements. However a comparison of the chemical composition of the aerosol revealed a considerably better agreement between the modelled and the measured aerosol components for ammonium, nitrate and sulfate, which are on average only 15–20% underestimated. Slightly worse agreement was determined for sea salt, that was only available at two sites. The largest discrepancies result from the aerosol mass which was not chemically specified by the measurements. The agreement between measurements and model is better in winter than in summer. The modelled organic aerosol mass is higher in summer than in winter but it is significantly underestimated by the model. This could be one of the main reasons for the discrepancies between measurements and model results. The other is that primary coarse particles are underestimated in the emissions. The probability distribution function of the PM10 measurements follows a log-normal distribution at most sites. The model is only able to reproduce this distribution function at non-coastal low altitude stations. The AOD derived from the model results is 20–70% lower than the values observed within AERONET. This is mainly attributed to the missing aerosol mass in the model. The day-to-day variability of the AOD and the log- normal distribution functions are quite well reproduced by the model. The seasonality on the other hand is underestimated by the model results because better agreement is achieved in winter.

online article

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Ground fog in Karlsruhe, Germany
Copyright: Bernhard Mühr

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