Summary	of	Interagency	Working	Comments	on	Draft	Language	under	

EO12866/13563	Interagency	Review.		Subject	to	Further	Policy	Review.

1

Environmental Protection Agency (EPA): Proposed Rule

Cross-State Air Pollution Rule for the 

2008 Ozone National Ambient Air Quality Standards

RIN 2060-AS05

Technical Support Document (TSD): Preparation of Emissions Inventories for the 

Version 6.2 2011 Emissions Modeling Platform

General Comments

1) Reviewer recommends that given the large number of exceptions, it would help to have a 

roughly quantitative estimate of how prevalent these are. For example, the section on 

spatial surrogates is one place where exceptions are handled clearly, but many other 

sections do not provide guidance on how important these exceptions are. 

a. From a bigger picture perspective, it would also be useful to have a brief 

qualitative discussion early on emphasizing that the models being used are largely 

state-of-the-art and thus, while there is likely significant uncertainty around the 

estimated emissions inventories, the approach attempts to reduce this uncertainty

through careful collection of data and benchmarking. This is an important caveat 

to the approach that should be somewhere.

Response: Preparation of emissions inventories for air quality modeling is a complex process. 

We are continually evaluating and improving the methods used to develop the emissions 

inventories along with the ancillary data that is used to prepare the data for air quality modeling.

The modeling performed for this rulemaking used the latest available inventories and ancillary

data. 

Specific Comments

1) Page 3 – Reviewer recommends either pointing out where the projection methods will be 

discussed later in the TSD or discuss those methods briefly here. It looks like they are 

discussed in Section 4.

a. “Because projected emission inventories had already been prepared for the year 

2018 by the time of the Natural Resources Defense Council v. EPA decision, the 

projected emissions for some sectors were adjusted to the year 2017 using 

methods appropriate to those sectors.” 

Response: The development of the projected inventories is discussed in Section 4. This

is mentioned at the end of Section 1.

2) Page 22 – Reviewer recommends understanding the degree to which the hoteling 

emission factors were imputed from nearby counties. Is this persuasive or occasional? 
Summary	of	Interagency	Working	Comments	on	Draft	Language	under	

EO12866/13563	Interagency	Review.		Subject	to	Further	Policy	Review.

2

How far off might the factors be? 

Response: There were 25 counties that were assigned to use hoteling emission factors 

from counties other than their standard representative counties. Because the factors were 

still from similar counties in the same states, the reassignment should not have a 

significant impact on the results.

3) Page 45 (top) – Reviewer recommends understanding what criterion was used to decide 

whether to integrate HAPs into a particular sector.

Response: This is discussed in sections 3.2.1.1 and 3.2.1.3 of the TSD. Generally we 

integrated sources other than prescribed and wild fires, many point sources - because the 

BAFM and VOC could potentially be reported at different processes within a facility

thereby making integration difficult, and sources where the sum of BAFM pollutants was 

greater than the VOC emissions. There is no need to integrate sources without emissions 

of BAFM pollutants. For the sector “othpt” we integrated only the C3 marine sources in 

this sector (see Section 2.4.2) because HAPs in this sector are derived identically to the 

U.S. c3marine sector. 

4) Page 49 (footnote 16) – How many select sources and select counties were affected by 

this error? Was this number large or small?

Response: A portion of the oil and gas sources in 98 counties were affected. The VOC 

speciation for these counties was performed based on national profiles instead of regionspecific ones. 

5) Page 57 (middle) – How much of the data is imputed with annual mean values? Is this 

appropriate rather than using seasonal mean values?

Response: We reviewed the version of the correction program more closely, and note that

monthly mean values are used when there is enough data available for that month. 

Annual average values are only used when there is not enough data for a particular 

month. The total amount of NOx reduced by this process was 6,600 tons out of 2,000,000

total tons of EGU NOx in 2011. Out of the 4,824 CEMS units, there were 1,344 units 

with at least one hour adjusted and the total amount of pre-adjusted NOx emissions at 

those units was 67,000 tons.

6) Page 65 (top) – For how many units is it not always possible to reallocate excess 

emissions to hours below the historic maximum and thus the regional fuel-specific 

average profile is used to impute the data? The graphs are beneficial, but the reviewer 

recommends providing a quantitative estimate. 
Summary	of	Interagency	Working	Comments	on	Draft	Language	under	

EO12866/13563	Interagency	Review.		Subject	to	Further	Policy	Review.

3

Response: There were 75 units for which regional profiles were applied because the 

emissions would not fit below the historic maxima.

7) Page 116 (bottom) – What percentage of the gas/oil play counties are covered by the 

AEO?

Response: The AEO gas and oil play data covers 302 of 1260 counties within the 

modeling domain with more than 5 tons of VOC emissions from oil and gas sources. 

These counties account for 56% of the VOC and 41% of the NOx emissions from oil and

gas-related sources.

8) Page 152 – Reviewer recommends mentioning that VMT has largely leveled off in the 

past several years although it is beginning to rise again, but that the AEO estimates, while 

showing a continued increase, are still reasonable forecasts because they extend the 

long-term trend.

Response: VMT trends can be seen at this site: 

https://www.fhwa.dot.gov/policyinformation/travel_monitoring/tvt.cfm. We concur with 

the reviewer that in the few years after 2011, VMT was pretty flat, but has shown a 3% 

increase in the 12 month rolling average for the period ending August, 2015 (see 

https://www.fhwa.dot.gov/policyinformation/travel_monitoring/15augtvt/15augtvt.pdf). 

The AEO estimates used for this analysis were consistent with the long-term trends that 

were available at that time. The VMT projections used for 2017 will be updated with the 

most recently available information to create the 2017 VMT used for the final rule 

modeling, as the proposal modeling was actually scaled back from 2018 values.