Investigating the behaviour of the CRI-MECH gas-phase chemistry scheme on a regional scale for different seasons using the WRF-Chem model

The behaviour of the CRI-MECH chemistry scheme was investigated over North-West Europe for the first week of each month for the year of 2015 using the mesoscale non-hydrostatic 3-D meteorological model, WRF-Chem. The model simulations of the distribution of important trace gas species (e.g. ozone, CO, NO, NO2 and SO2) were compared with ground-based measurements of selected rural and urban areas in UK. The model validation using the UK Defra Automatic Urban and Rural Network (AURN) measured data from sites across the UK showed a reasonable agreement between model-measurement for ozone (R=0.45 for rural sites and R=0.34 for urban sites), for NO2 (R=0.65 for rural sites and R=0.45 for urban sites) and for NO (R=0.35 for rural sites and R=0.22 for urban sites). However, a poor correlation between model-measurement is found for CO (R=0.15 for urban sites) and for SO2 (R=0.1 for rural sites and R=0.27 for urban sites). Further investigations showed a poorer performance of the model ozone, CO, NO and NO2 during summer and autumn months compared with winter months. The differences in model performance were most noticeable for ozone with the other species having more variance between sites and months. The possible causes for the deviations between the modelled and the measured data are discussed.