Often in Europe, high concentrations of O3 and NOx exceed the allowed maximum levels defined by the European Commission. The model system WRF-CMAQ is a regional air quality modelling system, which we applied to the European continent with a horizontal resolution of 12km × 12km and 8 vertical layers for CMAQ. The EMEP emission inventory was compiled and applied to the model domain. Due to uncertain external influence, the definition of adequate lateral boundary conditions for gas phase chemistry in a regional model is a complex issue and an important source of errors. Sensitivity studies were performed for a tested month (May 2004) to assess the impact of boundary conditions and boundary layer on the quality of the simulations. In order to evaluate the performances of the model, model simulations were compared to 70 and 21 stations from the EMEP network for O3 and NO2, respectively, throughout Europe. Basically, synthetic boundary conditions over 6 vertical layers were used in preliminary simulations. Then, climatological data provided by the global climate-chemistry model LMDz-INCA2 were used to define consistent lateral conditions and simulations were also performed using the May-2004 data from this model (both over 6 or 15 layers). Climatological data provided reliable conditions for the model boundaries but did not improve the quality of simulated O3 in the model domain (mean normalized gross error (MNGE) of 23% compared to 20% for synthetic profiles). Besides, the use of higher vertical resolution notably improved the trend and daily variations of O3 and hindered unrealistic subsidence of O3-enriched air from aloft, reducing the MNGE from 23% to 18%. The chemistry of NO2 was found to be mostly governed by local emissions, with little influence of the boundary conditions. A best-fitting configuration of boundary conditions will be discussed. Also, this work analyzes the influence of two different planetary boundary layer (PBL) parameterization schemes: the YSU PBL scheme based on Hong. et al (1996) and a new stable boundary layer scheme allowing the computation of vertical diffusion coefficients at all timesteps. The two schemes do not differ sufficiently from one another to lead to a significant improvement in the simulation of the chemistry. In the view of excessive NO2 simulated at night, other PBL parameterizations will be discussed.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- 0345 Pollution: urban and regional (0305;
- 0365 Troposphere: composition and chemistry;
- 0368 Troposphere: constituent transport and chemistry;
- 3307 Boundary layer processes