Metcombine combines 2-D gridded meteorology data with the 1st layer of 3-D gridded meteorology data to create custom files for on-road mobile processing with MOBILE6. To calculate humidity data for use in MOBILE6, the program Premobl needs temperature, pressure, and water vapor mixing ratio data in the same meteorology file. Pressure and mixing ratio data are typically found in the MET_CRO_3D file with the variable names PRES and QV, respectively. The MET_CRO_2D file usually contains ground-level temperatures (TEMPG), 1.5 meter temperatures (TEMP1P5), and 10 meter temperatures (TEMP10). While it is possible to use air temperature data from the MET_CRO_3D file (variable named TA), it is generally recommended to use temperature data from closer to the ground, i.e. ground or 1.5 meter temperatures from MET_CRO_2D. Metcombine is used to create custom meteorology files that contain the variables PRES, QV, and TEMPG (or any other temperature variable).

The program takes two I/O API NetCDF gridded meteorology files as input. The files must have identical grid paramaters, start dates and times, time steps, and run lengths. Metcombine is generally used to combine a 2-D file with a 3-D file, but the program is not restricted to that combination; it can be used to combine two 2-D files or the 1st layers of two 3-D files.