17.3 What Other Data are Needed to Support Emissions Modeling?

The emission inventories must be converted (through emissions modeling) from their

original resolution (e.g., database records) to input files for air quality models. These input files

generally require emissions to be specified by model grid cell, hour, and model chemical species.

This section describes the ancillary data that modelers should collect that allow emissions

models to convert the emission inventory data.

Ancillary data for temporal allocation are necessary for stationary point, stationary area,

and all mobile sources. To facilitate temporal allocation of the emissions, factors (called

profiles) must be created to convert annual emissions to specific months (monthly profiles),

average-day emissions to a specific day of the week (weekly profiles), and daily emissions to

hours of the day (hourly profiles). Additionally, a cross-reference file is needed to assign the

temporal profiles to the inventory records by SCC, facility, or some other inventory

characteristics. Where available, the operating information that may be available from the pointsource

inventory should be used to create inventory-specific temporal factors. EPA provides a

starting point for the temporal profiles and cross-reference files, available at:


For point sources, hourly Continuous Emissions Monitoring data are recommended for

use in model-evaluation runs. For future-year runs, we recommend creating an “average-year”or

“typical year” temporal allocation approach that creates representative emissions for the

“baseline inventory” but that also includes similar daily temporal variability as could be

expected for any given year. Care should be taken to not reduce or increase day-to-day


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