Impact of grid resolution on the predicted fine PM by a regional 3-D chemical transport model

This study examines the role of horizontal grid resolution on the performance of the regional three dimensional chemical transport model (CTM) PMCAMx. Two cases were investigated. First, the model was applied over the Northeastern United States with grid resolutions of 36 and 12 km during both a summer and a winter period. In this case the emission inventory was simply interpolated from the low resolution version. In the second case a multi-scale 36/4 km grid resolution is used over Western Europe with high resolution (4 × 4 km) emissions. The improvement in model predictions with the fine grid is modest during the summer and more significant during wintertime at both domains. Major differences are predicted mostly for primary (organics and black carbon (BC)) rather than secondary (e.g. sulfate) species. The use of high grid resolution decreases the bias for BC concentration by more than 30% in the Northeastern US during wintertime. In the Megacity of Paris, using high resolution emissions and a 4-km grid decreases the fractional bias for organic aerosol (OA) from 80% to 60% in the city center and produces much larger spatial concentration gradients in the domain as compared to the emissions being interpolated. These results suggest that future work should combine high grid resolution with high resolution emissions, taking into consideration, though, that the grid resolution is not currently the major source of the discrepancies between model predictions and observations.