6.10. Mrggrid

6.10.1. Description
6.10.2. Processing Order
6.10.3. Files and Environment Variables

6.10.1. Description

Processing categories: all

The purpose of the Mrggrid program is to combine gridded emission data files, which can be speciated or nonspeciated, and hourly or time-independent. It can combine any number of 3-D emissions files with any number of 2-D emissions files. In fact, this program will work with any I/O API NetCDF gridded files and need not be used only for emissions files. The program merges whatever data variables are in the input files. These files can each have different sets of data variables; Mrggrid will sum values only for each variable that is common to two or more files.

Mrggrid checks several features of the input files to ensure that the data in these files are appropriate to be merged together. All input files must have use the same time step. Mrggrid compares the units of the variables with the same name and it creates an error message when the units are not identical. It is not sufficient to have units that are the same in meaning but different in syntax. For example, although tons/hour and tons/hr represent the same units, Mrggrid will not recognize this because of the different syntax. The user must resolve unit discrepancies before running the program. In addition, Mrggrid compares the horizontal grid settings across all 2-D and 3-D files, and these settings must be identical in all respects (e.g., number of cells, grid cell size, grid projection). Finally, Mrggrid checks the layer structures across multiple 3-D files. The 3-D files can have a different number of layers, as long as any layer common to two or more files has the same thickness in each of the files; Mrggrid also checks the I/O API type of vertical structures and top height, and these must be identical across all 3-D files.