Evaluation of CMAQ Applications at Neighborhood Scales | US EPA Skip to main content Official websites use .gov A .gov website belongs to an official government organization in the United States. Secure .gov websites use HTTPS A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites. Evaluation of CMAQ Applications at Neighborhood Scales Introduction Related CMAQ Evaluation Links Model Evaluation Framework Incremental Evaluation of New CMAQ Versions Improving PM 2.5 Chemistry in CMAQ Air Quality Model Evaluation International Initiative (AQMEII) Dynamic Evaluation and Trend Analysis Eulerian air quality models, such as CMAQ, discretize large simulation domains into smaller sized grid cells in order to better represent spatial heterogeneities. In theory, smaller-sized grid cells provide a truer representation of fine-scale processes and near-field impacts. While utilizing larger grid cells has the advantage of minimizing computation resources, it does have several disadvantages. Since Eulerian air quality models instantly dilute point emissions across the entire volume of the grid cell, decisions on grid resolution should be made with consideration of the spatial scale of the air quality problem, meteorology, and emissions being modeled while also recognizing the increased computation resources required as grid cell size is decreased. The smaller the dimensions of the grid cells used, the more representative the model may be of the actual point source emissions. Additionally, meteorological fields (e.g. wind and temperature) are also likely to be better represented with smaller grid cells, particularly in areas with diverse and complex geography (e.g. coastal and mountainous regions). Examples of Fine-Scale CMAQ Applications: 2011 Baltimore-Washington D.C. DISCOVER-AQ Campaign 2013 San Joaquin Valley (SJV) California DISCOVER-AQ Campaign 2014 Colorado Front Range DISCOVER-AQ/FRAPPE Campaig