1. Emission Inventories 

To inform air quality modeling for the development of the 

final Transport Rule, EPA developed emission inventories for a 

2005 base year and for 2012 and 2014 projections. The 

inventories for all years include emission estimates for EGUs, 

non-EGU point sources, stationary nonpoint sources, onroad 

mobile sources, nonroad mobile sources, and biogenic (non-human) 

sources. EPA’s air quality modeling relies on this 

comprehensive set of emission inventories because emissions from 

multiple source categories are needed to model ambient air 

quality and to facilitate comparison of model outputs with 

ambient measurements. In addition, EPA considers all relevant 

emissions (regardless of source category) when determining 

whether a state is found to be significantly contributing to or 

interfering with maintenance of a particular NAAQS in another 

state. 

The emission inventories were processed through the Sparse 

Matrix Operator Kernel Emissions (SMOKE) Modeling System version 

2.6 to produce the gridded, hourly, speciated, model-ready 

emissions for input to the CAMx air quality model. Additional 

information on the development of the emission inventories and 

related data sets for emissions modeling are provided in the 

Emission Inventory Final Transport Rule TSD. 
On October 27, 2010, EPA issued a NODA on “Revisions to 

Emission Inventories.” The NODA’s primary purpose was to notify 

the public about changes to emission inventories made since the 

proposal modeling. The affected emission sectors were non-EGU 

stationary point sources, nonpoint sources, and Category 3 

commercial marine vessel sources. The NODA also presented a 

newly released model for developing onroad mobile source 

emissions for use in air quality modeling for the final 

Transport Rule. 

The major comments received in response to the emission 

inventories and modeling included in the proposed Transport Rule 

and the October 27 NODA are summarized in the following 

subsections. EPA agreed with the comments summarized below and 

adopted technical corrections or updates to the emission 

inventories and modeling accordingly. For EPA to be able to take 

appropriate action, comments on the emission inventories needed 

to be specific enough to allow for credible alternative data 

sources to be located. EPA adopted corrections from comments on 

in-place control programs or devices where the controls were 

enforceable and quantifiable. 

a. Foundation Emission Inventory Data Sets 

EPA developed emission data representing the year 2005 to 

support air quality modeling of a base year from which future 

air quality could be forecasted. EPA used the 2005 National 
Emission Inventory (NEI), version 2 from October 6, 2008, as the 

chief basis for the U.S. inventories supporting the 2005 air 

quality modeling. This inventory includes 2005-specific data 

for point and mobile sources, while most nonpoint data were 

carried forward from version 3 of the 2002 NEI. The future base 

case scenarios modeled for 2012 and 2014 represent predicted 

emission reductions primarily from already promulgated federal 

measures. 

EPA used a 2006 Canadian inventory and a 1999 Mexican 

inventory for the portions of Canada and Mexico within the air 

quality modeling domains for all modeled scenarios. Emissions 

from Canada and Mexico for all source sectors (including EGUs) 

in these countries were held constant for all base- and futureyear cases. EPA made this conservative assumption because it 

does not currently have sufficient data to support projections 

of future-year emissions from Canada and Mexico.