Adapting CMAQ to investigate air pollution in North Sea coastal regions

Abstract

The Models-3 Community Multiscale Air Quality (CMAQ) model is setup on a 54 × 54 km2 grid for Europe and on a nested smaller domain with a 18 × 18 km2 grid for the North Sea region. This paper concentrates on the models ability to represent the transport and deposition of atmospheric pollution in North Sea coastal areas. Comparisons to NO2 and PM10 measurements at selected sites of the Co-operative Program for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) are used for quality control for atmospheric concentrations. We use modeled nitrogen deposition fields and EMEP wet deposition measurements during January and July 2001 as a measure to evaluate the deposition schemes. Close agreement between the model and the measurements was found for the oxidised nitrogen compounds in January, when on average NO2 was overestimated by 18% (measured: 3.52 μg N/m3, modeled: 4.16 μg N/m3) and nitrate deposition was only slightly underestimated by 2%. However, ammonia was underestimated by 44%. In July, NO2 levels are much lower than in January and the model underestimates the mean concentration by 35% (measured 1.49 μg N/m3, modeled 0.97 μg N/m3). Wet deposition is also underestimated, but again the results for nitrate (−38%) were in better agreement with the measurements than for ammonium (−57%). PM10 concentrations are largely underestimated in January and July (by about 65% on average), but this result was expected, because only anthropogenic emissions were considered. Nevertheless, especially in January high daily correlations (0.69–0.84) between the modeled dry PM10 and the measurements in Germany were found. This indicates that the aerosol transport pathways are captured quite well by the model. CMAQ has been expanded to represent also persistent organic pollutants (POPs). In this paper first results of deposition fields of the carcinogenic benzo(a)pyrene (B(a)P) are shown. Preliminary comparisons to air concentration and deposition measurements show that the model results are in the right order of magnitude. In particular the observed strong seasonal cycle of B(a)P in air was also present in the model.