H14-79 PERFORMANCE EVALUATION OF WRF-MNEQA-CMAQ AND WRF-MNEQA-CHEM AIR QUALITY MODELLING SYSTEMS IN NORTH-EASTERN SPAIN

Using data from a case study performed during summer 2009 in the north-east of Spain, the WRF/Chem and WRF-CMAQ models were statistically evaluated and compared, focusing on ozone concentrations. It is shown that the WRF-CMAQ model provides a better forecast of O3 than WRF/Chem, although both models underestimate ozone concentrations. The major under-prediction of the WRF/Chem could be due to the direct effects of particulate matter on net short-wave radiation and semi-direct effects on air temperature and NO2 photolysis rate. The three-dimensional air quality models developed over the last 15-20 years consisted of a meteorological driver, an emissions module and a chemical transport model with the chemistry off-line solved. However, in the last few years, new generations of air quality models have been developed with the chemistry on-line solved with the meteorology because the simulation and prediction of air quality involves both meteorological factor and chemical processes. In the real atmosphere chemical and physical processes are coupled, as several factors such as wind speed and direction, turbulence, radiation, clouds, and precipitation interact with chemical processes such as deposition, and transformations. The chemistry can affect the meteorology, for example, through its effect on the radiation budget, as well as the interaction of aerosols with cloud condensation nuclei. Likewise, clouds and precipitation strongly influence chemical transformation and removal processes, and localized changes in the wind or turbulence fields continuously affect the chemical transport (Grell et al., 2005). In this contribution we present results from one case study using two different air quality modelling systems. The first system is an off-line matured modelling system based on the Weather Research and Forecasting (WRF) (Skamarock et al., 2005), using the mass coordinate version of the model, called Advanced Research Weather (ARW), coupled to the Community Model for Air Quality (CMAQ) (Byun and Ching, 1999). WRF is a mesoscale non-hydrostatic meteorological model, and the dispersion and chemical transport model CMAQ is one of the most up-to-date air quality dispersion chemical models. The second system is an on-line (one code, one system) tool to simulate air concentrations based on the WRF meteorological driver. In WRF/Chem the chemistry transport and transformations are embedded into WRF as part of the code (Grell et al., 2005), so the interactions between many meteorological variables and the chemistry properties can be explored and analyzed. The same emission model, MNEQA (Numerical Emission Model for Air Quality) (Ortega et al., 2009), was used in both models to test the performance of both modelling systems in forecasting high ozone concentrations that occurred during a case study corresponding to summer 2009 in north-eastern Spain (Catalonia). Comparison of WRF/CMAQ with observations as well as with WRF/Chem for the former pollutant provides the basis of our model evaluation. 2. MODELLING APPROACH Meteorological numerical simulations were performed using the WRF-ARW version 3.1. 1. The model was configured with three nested domains that have grids of 27, 9 and 3 km (Fig. 1), with a two-way interface with the smallest grid. The innermost domain, D1, covers 69x45 grid cells; D2, 70x70 cells; and D3, the inner domain corresponding to Catalonia (NE Spain) covers 94x94 grid cells. The vertical grid is common to all the domains, with 31 vertical levels and a resolution of 15 m close to the surface, decreasing gradually with height, thus enabling low-level flow details to be captured; the top of the domain was at 100 hPa. Initial and boundary conditions were taken from the European Centre for Medium Range Weather Forecasts (ECMWF) with a 1.5oX1. 5oresolution every 6 hours, and so boundary conditions could be updated at this time interval.