Standardize SO2 and NOx emission factor creation

[grgmiller]

The uncontrolled SO2 and NOx emission factor tables that we use are manually created based on two tables included as part of the EIA's Electric Power Annual. However, in copying these factors, applying them to prime movers that are not explicitly listed, and applying rules to determine which default value to use, there is a chance that we are introducing errors into the table. A better approach would be to add a data pipeline to download these files from EIA, transform them, and apply standardized, replicable, and transparent rules for implicit data types.

We may also need to look at emission factors from EPA since there are some factors that do not appear in the EIA tables.