After applying the growth factors to the SMOKE intermediate inventory file, the Grwinven program writes a new SMOKE intermediate inventory file that contains the new, grown emissions. Grwinven only writes the I/O API part of the inventory and not the ASCII part, because the ASCII part that contains the state/county codes, SCCs, and other character strings does not change between the base and future or past year. All of the sources in the base and grown inventory files are the same; the difference is in their emissions values.

Grwinven adds a header element to the I/O API part of the inventory file that indicates the file was created using Grwinven and a growth matrix. The header element is /FYEAR/, which is followed by the date of the future year (for example, /FYEAR/ 2018). Other programs (such as Temporal) will recognize the /FYEAR/ header element and alter its messages to indicate that a future year is being processed.

Grwinven can also output the IDA inventory format (in addition to I/O API format), which is also a SMOKE input format. This is possible only for inventories imported in EMS-95, IDA, or the nonroad SMOKE ORL format. Because the point and nonpoint toxics inventories contain additional fields that are not supported by the IDA format, Grwinven cannot output IDA format but output an ORL-formatted grown and/or controlled inventory when these formats were used to create the SMOKE intermediate inventory file. Currently only ORL nonpoint and point inventory formats are supported.