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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Technical Support Document

For the Review of

“Arizona State Implementation Plan Revision for the Nogales PM2.5

Nonattainment Area,” dated September 2013

And Its

Appendix A: “Primary PM2.5 and Secondary Precursor Emission 

Inventories for 2008 and 2010,” dated July 26, 2013,

As Submitted On September 6, 2013

By Arizona Department of Environmental Quality

Environmental Protection Agency – Region 9

Air Division

August 2014

Draft Final
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Summary

This Technical Support Document (TSD) provides detailed 

review, discussion, and supporting rationale for EPA’s proposed 

action on the “Arizona State Implementation Plan Revision for the 

Nogales PM2.5 Nonattainment Area” submitted on September 6, 2013 

and addressing fine particle (PM2.5) and precursor compounds 

emissions inventories for the Nogales nonattainment area.1 The 

supporting documentation cited in this TSD and Arizona’s 

submitted documents can be found in the docket for today’s 

action.2 

To summarize, we concur with the overall methodology, basis 

for allocating Santa Cruz County emissions to the Nogales 

nonattainment area, and allocation calculations used to produce 

the Nogales nonattainment area emissions inventories for PM2.5 and 

its precursor pollutants. We find that the Nogales nonattainment 

area calculated emissions inventories for PM2.5, ammonia (NH3), 

oxides of nitrogen (NOx), and sulfur dioxide (SO2), four of five 

emissions inventories submitted, show little or no variance from 

our comparison data base, the 2008 National Emissions Inventory 

 

1 See correspondence from Eric C. Massey, Director, Air Quality Division of 

the Arizona Department of Environmental Quality to Jared Blumenfeld, Regional 

Administrator, U.S. Environmental Protection Agency, Region IX, dated 

September 6, 2013, and submittal titled “Arizona State Implementation Plan 

Revision for the Nogales PM2.5 Nonattainment Area”.

2 An electronic version of the docket can be viewed by visiting 

Regulations.gov and entering the docket number for today’s action, EPA-R09-

OAR-2014-0450.
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

(NEI) version 3.0 emissions inventory. Even when considering its 

omitted source categories, the submitted total volatile organic 

compound (VOC) emissions inventory shows a small overall 

underestimate of 3 percent when compared to the corrected 2008

NEI version 3.0 Santa Cruz County baseline VOC emissions

inventory (see Table 6), and a slightly larger variance of 10

percent when compared to the submitted Nogales nonattainment area 

VOC emissions inventory (see Table 12). This small overall 

underestimate of VOC emissions is not significant, and becomes 

less significant when considered against an adjusted increase

provided by the submitted VOC on-road mobile emissions inventory 

to the reference 2008 NEI on-road mobile VOC emissions estimates 

(see Section 6). In this way, we consider the adjusted 

difference in the overall VOC emission inventory and our 

reference 2008 NEI version 3.0 emissions inventory to be closer 

to 3 percent rather than 10 percent, a small variance in the 

context of the overall PM2.5 emissions inventories. Consequently, 

we are proposing to find that Arizona’s submitted PM2.5, NH3, NOx, 

SO2, and VOC emissions inventories meet the Clean Air Act section 

172(c)(3) requirement to provide a comprehensive, accurate, and 

current inventory of actual emissions for the Nogales PM2.5

nonattainment area.

1.0 Background and Statutory Requirements

Effective December 14, 2009, EPA established the initial 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

air quality designations for most areas in the United States

regarding the 2006 24-hour PM2.5 National Ambient Air Quality 

Standard (NAAQS) (74 FR 58688, November 13, 2009). Among these 

areas, EPA designated the Nogales area in Arizona as 

nonattainment for the 2006 24-hour PM2.5 NAAQS. The boundaries

for the Nogales PM2.5 nonattainment area are described in 40 CFR 

81.303.3

On January 7, 2013, EPA finalized a determination that the 

Nogales nonattainment area had met the 2006 24-hour PM2.5 NAAQS

(78 FR 887). This determination of attainment was based on 

complete, quality-assured, and certified ambient air quality 

data showing that the Nogales area had monitored attainment of 

the 2006 24-hour PM2.5 NAAQS over three consecutive years, from 

2009 to 2011. Given this determination, EPA applied its Clean 

Data Policy and suspended the requirements for the Nogales area 

to submit an attainment demonstration, reasonably available

control measures, a reasonable further progress (RFP) plan, and 

contingency measures for failure to meet RFP and attainment 

deadlines for so long as the area continues to attain the 2006 

24-hour PM2.5 NAAQS. The emissions inventory submittal 

requirement in CAA section 172(c)(3), however, is not suspended 

 

3 The Nogales PM2.5 nonattainment area is located in southern Santa Cruz 

County, Arizona, covering 76.1 square miles and is adjacent to the 

international border with Mexico. See Figure 1.1 of the submittal. 
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by way of this determination of attainment and the application 

of EPA’s Clean Data Policy.4 

Section 172(c)(3) of the CAA requires a state with an area 

designated as nonattainment for a NAAQS to submit a 

comprehensive, accurate, and current inventory of actual 

emissions for the nonattainment area for EPA’s review and 

approval. EPA’s requirements for an emissions inventory for the 

PM2.5 NAAQS are set forth in 40 CFR 51.1008.5,6 For the PM2.5 

NAAQS, the pollutants that must be inventoried are directly 

emitted PM2.5, NH3, NOx, SO2, and VOC.7 

2.0 Arizona’s Submittal

On September 6, 2013, Arizona submitted “Arizona State 

 

4 For EPA’s complete review of Nogales PM2.5 air quality data and discussion of 

EPA’s application the Clean Data Policy, please see our proposed rule at 77 

FR 65656, (October 30, 2012).

5 40 CFR 51.1008 (a)(2) and (b) do not apply for the Nogales area because they 

relate to requirements for attainment demonstrations and reasonable further 

progress (RFP); these requirements were suspended for the Nogales PM2.5 

nonattainment area so long as the area continues to meet the PM2.5 standard. 

For further discussion please see our final rule at 78 FR 887 (January 7, 

2013) and proposed rule at 77 FR 65656 (October 30, 2012).

6 Although the U.S. Court of Appeals for the District of Columbia (DC Circuit) 

recently remanded this rule and directed EPA to re-promulgate it pursuant to 

subpart 4 of part D, title I of the CAA (see Natural Resources Defense 

Council v. EPA, 706 F.3d 428 (D.C. Cir. 2013)), the court’s ruling in this 

case does not affect EPA’s action on these emissions inventories. Subpart 4 

of part D, title I of the Act contains no specific provision governing 

emissions inventories for PM10 or PM2.5 nonattainment areas that supersedes the 

general emissions inventory requirement for all nonattainment areas in CAA 

section 172(c)(3). See “State Implementation Plans; General Preamble for the 

Implementation of Title I of the Clean Air Act Amendments of 1990,” 57 FR 

13498, (April 16, 1992).

7 Emissions Inventory Guidance for Implementation of Ozone and Particulate 

Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze 

Regulations, EPA-454/R-05-001, August 2005, updated November 2005. 

http://www.epa.gov/ttn/chief/eidocs/eiguid/eiguidfinal_nov2005.pdf.
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Implementation Plan Revision for the Nogales PM2.5 Nonattainment 

Area”. Appendix A of this submittal contains the “Primary PM2.5

and Secondary Precursor Emission Inventories for 2008 and 2010,

which is hereafter referred to as “Appendix A.” Because much of 

the emissions inventory information and analyses are located 

within Appendix A, this appendix is the primary focus of EPA’s 

review in this TSD. 

3.0 Review of Emissions Inventory and Appendix A Methodology

Most of Arizona’s submitted Nogales nonattainment area

primary PM2.5 and secondary precursor emissions inventories for 

2008 and 2010 are derived from the data in EPA’s 2008 National 

Emission Inventory (NEI) versions 1.5 and 2.0 for Santa Cruz

County, Arizona. See Appendix A, section 3, page 5. Starting 

with 2008 NEI Santa Cruz County emissions estimates, ADEQ

allocated the share of nonattainment area emissions from countylevel emissions estimates by one of three characteristics and 

their related percentages: (1) human-induced activities/source 

categories were allocated by nonattainment area population 

share, 66.1 percent; (2) location-based activities/source 

categories were allocated by nonattainment area share of land 

area, 6.15 percent; and, (3) location specific sources, such as 

point sources, were fully allocated to the nonattainment area, 

as applicable. In the case of on-road mobile source emission 

estimates, Santa Cruz County emissions were estimated using the 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

EPA approved Motor Vehicle Emissions Simulator (MOVES) 2010b

model and then allocated by nonattainment area population share. 

See Appendix A, Table 3.1, page 8, for population and land area 

allocation ratios; and, see Appendix A, section 2, page 4, for 

their derivation. 

Next, ADEQ produced 2010 emissions inventories estimates 

for the Nogales nonattainment area from 2008 levels using a 2008 

to 2010 population-based growth rate of 1.1 percent for source 

categories that track with population growth. For source 

categories tied to economic activity, no growth was assumed due 

to the continued economic recession during the 2008 to 2010 

period. See Appendix A, section 3.4, page 9 for ADEQ’s 2010 

methodology discussion. The 2008 emissions inventories provide 

a calculation baseline for the 2010 emissions inventories. In 

turn, the 2010 emissions inventories provide an emissions 

estimate consistent with the time period (2009 to 2011) that EPA 

used to determine that the Nogales area was meeting the PM2.5

NAAQS. 

Upon review of this methodology, we find it acceptable and 

based on reliable estimates of population and land area. ADEQ’s 

population estimates are Arizona Department of Administration 

estimates that have been compared and reconciled with U.S. 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Census figures.8 We have verified the land area allocation ratio 

using geographical information system applications. We concur 

in the location and magnitude of point source emissions, which 

are discussed further in section 5.2, below.

4.0 Review of Source Category and Pollutant Estimates for Santa 

Cruz County

In our review, we compared ADEQ’s submitted Santa Cruz 

County estimates for PM2.5 and the precursor pollutants with the 

2008 NEI version 3.0. We reasoned that we would find nominal 

differences between the versions (1.5 and 2.0) used by ADEQ and 

the final version (3.0) of the NEI based on corrections and reestimates. EPA’s 2006 PM2.5 NAAQS implementation guidance 

required a December 2012 submittal of these Nogales area 

emissions inventories. Due to an intervening court decree 

vacating portions of this guidance related to state submittals, 

we advised ADEQ not to submit the Nogales PM2.5 emissions 

inventory until we could provide guidance following the court’s 

decision (see footnote 6 for discussion and resolution). 

Consequently, the 2008 NEI version 3.0 was released in March 2013 

prior to the submittal of the Nogales area PM2.5 emissions 

inventory in September 2013. While we did not require ADEQ to 

 

8 See page 29 (Appendix A) of Appendix A for 2008 and 2010 population 

estimates used by Arizona and derivation of 1.1 percent population growth 

rate from 2008 to 2010.
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

use NEI version 3.0, given their emissions inventory was already 

drafted, we are reviewing the submittal against NEI version 3.0 

to ensure that any subsequent corrections or updates to the NEI

reflect only nominal variances with Arizona’s submitted emissions 

inventories. The 2011 NEI version 1.0 was released on September 

30, 2013; consequently, it was not available to ADEQ for use in 

their submittal. This review is presented in a manner similar to 

the methodology used by ADEQ in their submittal. Because the 

2008 Santa Cruz County emissions estimates provide the overall 

baseline for calculations, they will be reviewed first, followed 

by the 2008 and 2010 Nogales nonattainment area emissions 

estimates. 

A comparison of the submitted Santa Cruz County emissions 

inventories with the 2008 NEI version 3.0 emissions inventories 

shows slight differences among the totals, a percentage 

difference of 1 to 7 percent. See Table 1 below. Across source 

categories, the non-road mobile source category shows more 

variance relative to the other source categories. Across 

pollutants, the submitted VOC estimates show the largest variance 

from the 2008 NEI version 3.0 inventory, plus or minus 23 percent 

for on-road mobile sources and non-point sources. Consequently, 

we will review in more detail the non-road mobile source category 

and the VOC emissions inventory to determine the cause of the 

differing emissions estimates. Before doing so, we will first 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Table 1, Comparison of 2008 Estimates of PM2.5 and Precursor Pollutants for 

Santa Cruz County, Arizona: ADEQ Estimates (submitted) versus NEI version 3 

estimates (uncorrected), Tons Per Year

Pollutant by Source 

Category

ADEQ 

Estimates 

(submitted)

NEI version 3 

Estimates 

(uncorrected)

Difference 

(NEI vs. 

ADEQ)

Percentage 

Difference

PM2.5, Fine Particulates

Non-road Mobile Sources 19.9 21.9 2.0 10%

Non-Point Sources 656.1 656.4 0.3 0%

On-Road Mobile sources 38.0 41.8 3.8 10%

Point Sources(see note) --- --- --- ---

Total 714.0 720.1 6.1 1%

NH3, Ammonia

Non-road Mobile Sources 0.1 0.3 0.2 150%

Non-Point Sources 173.6 176.8 3.2 2%

On-Road Mobile sources 21.8 20.7 -1.1 -5%

Point Sources --- --- --- ---

Total 195.6 197.8 2.2 1%

NOx, Oxides of Nitrogen

Non-road Mobile Sources 216.3 269.3 53.0 24%

Non-Point Sources 91.0 91.4 0.5 0%

On-Road Mobile sources 1381.6 1398.5 16.9 1%

Point Sources --- --- --- ---

Total 1688.8 1759.2 70.4 4%

SO2, Sulfur Dioxide

Non-road Mobile Sources 4.2 4.9 0.7 16%

Non-Point Sources 47.5 48.1 0.6 1%

On-Road Mobile sources 11.3 11.8 0.5 4%

Point Sources --- --- --- ---

Total 63.1 64.8 1.7 3%

VOC, Volatile Organic Compounds 

Non-road Mobile Sources 240.0 252.3 12.4 5%

Non-Point Sources 1420.3 1729.4 309.2 22%

On-Road Mobile sources 645.0 494.2 -150.8 -23%

Point Sources --- --- --- ---

Total 2305.2 2475.9 170.7 7%

Note: Point sources are not listed because they are specific to the Nogales 

nonattainment area; see section 5.2 for our point source discussion. NEI VOC 

emission estimates shown here do not reflect the corrections described later 

in this document. 

Source: Appendix A, Section 4, Tables.

review the differences between the ADEQ emissions inventory and 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

the 2008 NEI that are described within their submittal, then we 

will review the submittal for undocumented variances from the 

NEI, particularly within the non-road mobile emissions estimates 

and VOC emissions inventory. 

4.1 ADEQ Documented Adjustments and Corrections 

In generating the pollutant specific emissions inventories 

for the individual source categories, ADEQ used the Santa Cruz 

County emissions estimates from the 2008 NEI versions 1.5 and 

2.0. In some instances, however, ADEQ revised the 2008 NEI data, 

either based on more accurate local information, or to correct 

errors they found in the data. See Appendix A, section 3.2.1, 

page 7 and section 4.1, page 10.

As described in section 3.2.1 of Appendix A, ADEQ did not 

generate reasonably accurate 2008 values for SO2 and VOCs while 

estimating on-road mobile emissions. After consulting with EPARegion 9 staff, ADEQ applied an agreed upon methodology to 

produce more reasonable results. See Appendix A’s appendices D 

and E for discussion and calculations. 

In section 4.1, ADEQ documented two adjustments to the 2008 

NEI data. While documented in Arizona’s submittal, these 

adjustments may not be reflected in the 2008 NEI version 3 

database at this time. The first adjustment concerned NH3

emissions from swine livestock operations. ADEQ adjusted the 

estimate for this source category from 209.9 tons per year to 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

0.14 tons per year, based on U.S. Department of Agriculture 

reported hog and pig populations for Santa Cruz County and 

updated emission factor information. The second adjustment 

concerned a recurring error in the 2008 NEI data for Arizona 

where a 761.1 ton per year PM10 estimate for mining activities 

was replicated across all Arizona counties. After an 

investigation in the Nogales nonattainment area disclosed no

mining sources, the PM2.5 emissions related to mining activity 

were removed from the submitted emissions inventory.

Upon review of the rationale and documentation presented 

for these adjustments to the 2008 NEI data, we concur with ADEQ’s 

emissions estimates. These documented changes do not, however, 

explain the differences we observed within the non-road mobile 

source category and the VOC emissions inventory, reviewed further 

below. 

4.2 Undocumented Adjustments to 2008 NEI Emissions Estimates

As discussed above, while most of the pollutant estimates 

differ slightly as to overall total compared to the 2008 NEI, 

version 3.0, the non-road mobile source category shows the 

largest cross pollutant differences and the VOC emissions 

inventory shows the largest individual inter-pollutant

differences. Because it crosses all the pollutant inventories, 

the non-road source category will be presented first followed by 

the review of the VOC emissions inventory. 
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4.2.1 Non-Road Mobile Source Category Review

Our detailed review of the non-road mobile source category 

showed that two source categories were not included in the ADEQ 

emissions inventory: locomotive emissions were not included in 

any pollutant inventories; and, pleasure craft, 2-stroke and 4-

stroke gasoline engines were not included within the VOC 

emissions inventory. See Appendix A, Table 4.1, pages 12-13. 

Table 2 below provides a comparison of the differences in 

each source category once locomotive emissions are considered. A 

large proportion of the differences in non-road mobile source 

category emissions of PM2.5, NOx, and SO2 are explained by the 

omission of locomotive emissions. The variances across 

pollutants when compared to total pollutant emissions, however, 

may be insignificant. For example, consider that NOx, the 

largest omitted locomotive pollutant, amounts to approximately 3 

percent of total NOx emissions.

Table 2, Comparison of 2008 Santa Cruz County Non-Road Mobile Emission 

Estimates: ADEQ Submitted versus Locomotive Emissions, (NEI version 3.0) 

All Pollutants (Tons)

Difference

(NEI vs.

ADEQ)

Mobile, 

Locomotive 

Emissions

Percent 

Difference 

Explained

PM2.5, Fine Particulates 2 1.6 80%

NH3, Ammonia 0.2 0.02 10%

NOx, Oxides of Nitrogen 53 49.5 93%

SO2, Sulfur Dioxide 0.7 0.5 71%

VOC, Volatile Organic Compounds 12.4 2.5 20%

Note: “Difference” estimate taken from Table 1, above. 

The remainder of the disparity between the submitted VOC 
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emissions inventory and the 2008 NEI version 3.0 VOC emissions 

estimate for non-road mobile VOC emissions is accounted for by 

missing emissions estimates from the pleasure craft 2- and 4-

stroke gasoline engine source category. These emissions equal 

10.6 tons per year (estimate includes exhaust, refueling, and 

evaporative emissions), approximately equal to the 9.9 tons left 

unexplained by the locomotive emissions estimate. While it is

possible there are no bodies of water in Santa Cruz County or the 

Nogales nonattainment area to support a pleasure craft emissions 

estimate, ADEQ did not explain this omission in its submittal. 

4.2.2 VOC Emissions Inventory Review

Our review of ADEQ’s submitted Santa Cruz County emissions 

inventory and the published County NEI version 3.0 emissions 

inventory disclosed disparities and errors within each emissions 

inventory, ADEQ’s submittal and EPA’s NEI version 3.0 reference 

document. We review here each County VOC emissions inventory to 

produce a corrected version of each for further comparison and 

reconciliation. 

When comparing ADEQ’s submitted VOC emissions inventory

with the 2008 NEI version 3.0 VOC emissions inventory, we found 

that the consumer, personal care products source category was 

entered twice in the 2008 NEI inventory database under different 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

source codes, once by ADEQ and again by EPA.9 After review, we 

set aside the ADEQ submitted emissions estimate for consumer, 

personal care products of 20.6 tons from the non-point source 

category estimate in both inventories, submitted and 2008 NEI 

version 3, (see Tables 3 and 4 below) in favor of retaining the 

EPA emissions estimate (see Table 7 below). This leaves 1399.7 

tons per year in the ADEQ VOC emissions inventory, see Table 3 

below, which reflects the correction.

Table 3, Corrected ADEQ VOC Estimates for Santa Cruz County 2008 (Tons)

Source Category ADEQ Submitted 

Estimates

Corrected ADEQ 

Estimates

Non-road Mobile Sources 240.0 240.0

Non-Point Sources 1420.3 1399.7

On-Road Mobile sources 645.0 645.0

Point Sources --- ---

Total 2305.2 2284.7

Next, we did a similar exercise for the published 2008 NEI 

version 3.0 VOC emissions inventory for Santa Cruz County and our 

detailed review found double entries or errors in the subcategories listed in table 4 below. 

Table 4, 2008 NEI version 3.0 VOC Non-Point Source Category Corrections by 

Sub-category, Emissions Estimates Removed (Tons) 

Consumer & Commercial, Household Products 38.6

Consumer & Commercial, FIFRA Related Products 38.2

Consumer, Pesticide Application 29.4

Consumer, Personal Care Products 20.6

Total 126.8

 

9 ADEQ’s submittal and line item entry to the 2008 NEI used standard source 

code (SCC) 2465100000, (20.6 tons), instead EPA used SCC 2460100000 (40.8 

tons).
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Consequently these entries were removed from our comparison NEI 

version 3.0 emissions inventory leaving the corrected non-point

and VOC emissions inventory below in Table 5.

Table 5, Corrected 2008 NEI version 3.0 VOC Estimates for Santa Cruz County 

(Tons)

Source Category NEI version 3.0

Estimates

Corrected NEI version

3.0 Estimates

Non-road Mobile Sources 252.3 252.3

Non-Point Sources 1729.4 1602.6

On-Road Mobile sources 494.2 494.2

Point Sources --- ---

Total 2475.9 2349.1

Comparing the corrected VOC emissions inventory data from 

the submittal and the 2008 NEI version 3.0 produces a difference 

of 64.4 tons, as shown in Table 6 below. 

Table 6, Comparison of 2008 Santa Cruz County VOC Emissions Estimates: 

Corrected ADEQ Versus Corrected 2008 NEI version 3.0 (Tons) 

Source Category

Corrected 

ADEQ 

Estimates

Corrected 

NEI V3.0

Estimates Difference

Non-road Mobile Sources 240 252.3 -12.3

Non-Point Sources 1399.7 1602.6 -202.9

On-Road Mobile sources 645 494.2 150.8

Point Sources --- --- ---

Total 2284.7 2349.1 -64.4

 

To review the VOC source category differences presented in 

Table 6, we have explained the differences in the non-road mobile

sources emissions inventory in Section 4.2.1, above. The 

difference in the on-road mobile sources is explained by the 

different estimation techniques used by EPA in generating the 

2008 NEI estimate compared to ADEQ’s use of the MOVES model. 
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This difference is discussed next in section 4.2.2.1 of this TSD, 

followed by our further review of the non-point source VOC 

emissions estimate, in Section 4.2.2.2.

4.2.2.1 On-Road Mobile Source VOC Emissions Estimates

In estimating on-road mobile VOC emissions estimates for 

the 2008 NEI (all versions), EPA integrated the MOVES on-road 

mobile emissions factor model with the SMOKE19 emissions

inventory model (hereafter referred to as “SMOKE-MOVES”) to take 

advantage of the gridded hourly temperature information 

available from meteorological data and to better account for the

temperature sensitivity of on-road emissions.10 SMOKE-MOVES 

requires emission rate “lookup” tables generated by MOVES that 

differentiate emissions by process (running, start-up, vapor 

venting, etc.), vehicle type, temperature, speed, and hour of 

day, among other parameters. To generate the MOVES emission 

rates that could be applied across the United States (U.S.), EPA 

used an automated process to run MOVES to produce emission 

factors by temperature and speed for 146 “representative 

counties” to which every other U.S. county could be mapped. In 

the case of Arizona’s submitted emissions inventories, we 

believe that the on-road mobile VOC emissions estimates provided 

 

10 2008 National Emissions Inventory, version 3 Technical Support Document 

(Draft), U.S. Environmental Protection Agency, Office of Air Quality Planning 

and Standards, September 2013, pp. 112-123. See the following link: 

http://www.epa.gov/ttn/chief/net/2008neiv3/2008_neiv3_tsd_draft.pdf
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by ADEQ are a more accurate and representative estimate because 

they are specific to Santa Cruz County, rather than a 

representation of the County, as used by EPA in the NEI to 

produce emission rates that could be used nationally.

4.2.2.2 Non-point Source VOC Emissions Estimates 

A comparison of the corrected ADEQ and NEI version 3.0 nonpoint source VOC emissions inventories shows undocumented 

omissions of several source categories within the submitted VOC 

emissions inventory. See Table 7 below. These omitted source 

categories account for the 202.9 tons difference between the two 

non-point source emissions estimates for ADEQ and the NEI

version 3.0, shown in Table 6. 

Table 7, 2008 NEI version 3.0 Santa Cruz County Non-point Source VOC 

Emissions Omitted from ADEQ 2008 Emissions Estimates (Tons) 

Source Category

Dry Cleaning, All Processes 2.9

Consumer & Commercial, All Personal Care Products 40.8

Consumer & Commercial, All Auto Aftermarket Products 29.2

Consumer & Commercial, All Coatings & Related Products 20.4

Consumer & Commercial, All Adhesives & Sealants 12.2

Consumer & Commercial, Misc. Products (Not covered elsewhere) 1.5

Surface Coatings, Architectural Coatings 51.7

Surface Coatings, Traffic Markings 13.0

Surface Coatings, Machinery & Equipment: SIC 35 0.1

Petroleum Product Storage, Residential & Commercial Portable Gas Cans* 26.7

Petroleum Product Storage, Airport/Aviation Gasoline: Stage 1 losses 3.3

Petroleum Product Storage, Airport/Aviation Gasoline: Stage 2 losses 0.2

Petroleum Product Storage, Storage & Transport, Trucks 0.7

Total 202.7

*Includes permeation, evaporation, diurnal losses, vapor displacement in 

filling, and spillage.
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4.2.3 Ammonia, Non-point Source Emissions Estimates

Our review of the Santa Cruz County ammonia emissions 

inventory showed that non-point source, residential fuel 

combustion natural gas emissions in the amount of 2.9 tons was 

omitted from the ADEQ submittal. While not significant in 

magnitude, this omission explains a large proportion of the 

difference in non-point source ammonia emissions between the 

ADEQ submittal and the 2008 NEI version 3.0. See Table 1, 

above.

5.0 Nogales Nonattainment Area Estimates

As explained in our review of the ADEQ submitted emissions 

inventory methodology, most of the Santa Cruz County emissions 

estimates are allocated to the Nogales nonattainment area by two 

factors, population size and land area. Most source category 

emissions were allocated by population, with the following 

exceptions: agriculture and related activities and prescribed 

forest burning emissions were allocated by land area; point 

source emissions were allocated by location within the Nogales 

nonattainment area. The tables in Section 4 of Appendix A show 

the individual allocations for each source category. See 

Appendix A, Tables 4.1-4.4. We concur with the allocation 

assignments ADEQ has chosen.

Section 5 of Appendix A describes the methods for 

estimating 2010 Nogales nonattainment area emissions inventories 
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from the 2008 emissions inventories. In general, population 

based human activity and resulting emissions were forecasted to 

grow at the same rate as population growth from 2008 to 2010, 

1.1 percent. See pages 9 and 29 of Appendix A. For source 

categories that represented an economic enterprise/activity, 

those resulting emissions were assigned a no-growth factor, 

given the economic recession of the time period. ADEQ developed 

2010 on-road mobile emissions estimates for Santa Cruz County

via MOVES as described in section 3.2.1 of Appendix A and 

allocated by population. Point source estimates for 2010 were 

held constant, again assuming no-growth because of the economic 

recession of the time period. The tables within Section 5 of 

Appendix A show the individual growth assignment for each source 

category. We concur in the assignments ADEQ has chosen.

Notable exceptions from the population and land use 

allocation rationale are locomotive emissions and point source 

emissions. We review each source category below in Sections 5.1 

and 5.2.

5.1 Locomotive Emissions Estimates

Santa Cruz County locomotive activity and resulting 

emissions may be allocated by estimating track mileage in the 

Nogales nonattainment area. Using GIS mapping, we estimate that 

11 of 29.8 county track miles are in the Nogales nonattainment 

area; therefore, the allocation ratio is 0.4. Consistent with 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

other economic activities and their expected growth, we assume 

that there was no growth in rail travel and transport of goods, 

given the economic recession of the time period. See Table 8 

below for results. 

Table 8, 2008 and 2010 Non-Road Mobile, Locomotive Emissions Allocated to 

Nogales Nonattainment Area, NEI version 3.0 (Tons)

All Pollutants

Santa Cruz 

County

Nogales 

Nonattainment Area

PM2.5, Fine Particulates 1.6 0.64

NH3, Ammonia 0.02 0.008

NOx, Oxides of Nitrogen 49.5 19.8

SO2, Sulfur Dioxide 0.5 0.2

VOC, Volatile Organic Compounds 2.5 1.0

5.2 Point Source Emissions Estimates

ADEQ determined that there are two point sources in the 

Nogales nonattainment area: the Nogales International Airport 

and the Valencia Power Plant. We concur with their findings and 

individual estimates for each source. The 2008 and 2010 

individual emissions estimates for these two point sources are 

provided in Appendix A, Table 4.4 and Table 5.4, respectively, 

and assume no growth given the economic recession during this 

timeframe. See Table 9 below for an aggregated presentation of 

estimated point source emissions.
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Table 9, 2008 and 2010 Nogales Nonattainment Area Point Source Emissions 

(Tons)

All Pollutants

Nogales 

Nonattainment Area

PM2.5, Fine Particulates 1.4

NH3, Ammonia ---

NOx, Oxides of Nitrogen 11.1

SO2,Sulfur Dioxide 0.5

VOC, Volatile Organic Compounds 3.3

5.3 Estimated Omissions in Submitted Nogales Nonattainment Area 

Emissions Inventories

In this section, we consolidate and present the emissions 

not accounted for within the submitted Nogales PM2.5 and precursor 

pollutant inventories. 

 Within the PM2.5, NOx, and SO2 emissions inventories, the 

non-road locomotive emissions not accounted for are 0.64, 

19.8, and 0.2 tons per year, respectively. See Table 8 

above for the derivation of Nogales nonattainment area 

emission estimates from Santa Cruz County estimates.

 Within the NH3 emissions inventory, the omitted emissions 

from the non-point source, residential fuel combustion, 

natural gas source category equal 1.9 tons per year when 

allocated from the Santa Cruz County emissions estimate to 

the Nogales nonattainment area by the population allocation 

factor (0.661). See Section 4.2.3 above. 

 We determined that the submitted VOC emissions inventory had 

the largest number of source categories and amount of 
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emissions estimates omitted from the reference 2008 NEI 

version 3.0 VOC emissions inventory. With the exception of 

non-road locomotive emissions, the Santa Cruz County 

emissions are estimated and allocated to the Nogales 

nonattainment area by the population allocation factor 

(0.661). See Table 10 below.

Table 10, Estimated Nogales Nonattainment Area VOC Emissions Omitted from 

ADEQ 2008 Emissions Estimates (Tons)

Source Category

Santa 

Cruz 

County

Nogales 

NA

Dry Cleaning, All Processes 2.9 1.9

Consumer & Commercial, All Personal Care Products 40.8 27.0

Consumer & Commercial, All Auto Aftermarket Products 29.2 19.3

Consumer & Commercial, All Coatings & Related Products 20.4 13.5

Consumer & Commercial, All Adhesives & Sealants 12.2 8.1

Consumer & Commercial, Misc. Products (Not covered elsewhere) 1.5 1.0

Surface Coatings, Architectural Coatings 51.7 34.2

Surface Coatings, Traffic Markings 13.0 8.6

Surface Coatings, Machinery & Equipment: SIC 35 0.1 0.07

Petroleum Product Storage, Residential & Commercial Portable Gas Cans* 26.7 17.6

Petroleum Product Storage, Airport/Aviation Gasoline: Stage 1 losses 3.3 2.2

Petroleum Product Storage, Airport/Aviation Gasoline: Stage 2 losses 0.2 0.1

Petroleum Product Storage, Storage & Transport, Trucks 0.7 0.5

Non-road Mobile, Locomotive 2.5 1

Non-road Mobile, 2- and 4- Stroke Gasoline Engines, Pleasure Craft 10.6 7.1

Total 202.7 142.2

*Includes permeation, evaporation, diurnal losses, vapor displacement in 

filling, and spillage

5.4 Review and Analysis of Total Emissions Estimates and Omitted 

Emissions Estimates

The total emissions estimates for each pollutant show a 0-

15 percent reduction from 2008 to 2010. The emissions reductions 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

are primarily due to federally mandated engine standards and 

cleaner burning diesel fuels causing reductions in on-road mobile 

source emissions. See Table 11 below and Appendix A, Table 6.1

for detailed source category estimates.

Table 11, Nogales Nonattainment Area Estimated Emissions (Tons)

Pollutant 2008 2010 Percent 

Change

PM2.5, Fine Particulates 435.6 433.9 0%

NH3, Ammonia 37.4 36.1 -3%

NOx, Oxides of Nitrogen 1115.4 946.8 -15%

SO2, Sulfur Dioxide 39.1 36.2 -7%

VOC, Volatile Organic Compounds 1490.8 1445.0 -3%

Source: Appendix A, Table 6.1, page 28.

These emissions estimates are not corrected, per the above 

discussion, because we will propose to approve the emissions 

inventories as submitted.

To assess the magnitude of the previously identified 

omitted emissions estimates for all pollutants, but primarily VOC

and NOx, the omitted emissions estimates were compared to the 

submitted total estimates for each pollutant (see Table 12

below). The range of variability is 0-10 percent, with VOC 

emissions being under-reported by 10 percent. The four remaining 

pollutant emissions inventories show an under-estimate of 5 

percent or less.
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

Table 12, Comparison of ADEQ’s 2008 and 2010 Nogales Nonattainment Area 

Estimated Emissions to Omitted Emissions by Pollutant.

Pollutant Estimated 

Omissions 2008 Percent of 2008 2010 Percent of 2010

PM2.5, Fine Particulates 0.6 435.6 0% 433.9 0%

NH3, Ammonia 1.9 37.4 5% 36.1 5%

NOx, Oxides of Nitrogen 19.8 1115.4 2% 946.8 2%

SO2, Sulfur Dioxide 0.2 39.1 1% 36.2 1%

VOC, Volatile Organic 

Compounds 142.2 1490.8 10% 1445.0 10%

Source: 2008 and 2010 emissions are taken from Appendix A, Table 6.1. 

Estimated omissions are taken from Tables 8 and 10 of this TSD, and ammonia 

non-point emissions estimates. See Section 5.3 above for derivation of 

estimated omissions. 

6.0 Summary and Conclusion

We concur with the overall methodology, basis for 

allocating county-level emissions to the nonattainment area, and 

allocation calculations used to produce the Nogales nonattainment 

area emissions inventories for PM2.5 and its precursor pollutants. 

Considering the review of and comparisons between the submitted 

baseline 2008 Santa Cruz County emissions and the subsequent NEI 

version 3.0, we found the range of variability to be 1-7 percent 

when considering the uncorrected totals within the emissions

inventory databases (see Table 1 of this TSD). After the 

emissions estimates were corrected, the variance of the total VOC 

emissions estimate, the source category with the highest total 

difference, is reduced to 3 percent (see Table 6). As presented 

in Table 12, NEI version 3.0 emissions data omitted from the 

submitted Nogales nonattainment area emissions inventories range 

from 0-10 percent with four of five pollutant inventories showing 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

equal to or less than 5 percent total variance or underreporting, and three of the pollutant inventories showing 2 

percent or less variance or under-reporting.

With regard to the completeness of the submitted emissions 

inventories and overall emissions estimates for the Nogales 

nonattainment area, ADEQ’s omission of the locomotive source 

category slightly affects the overall Nogales nonattainment area 

emissions estimates for PM2.5, NOx, and SO2 (see Table 12). The NH3

emissions inventory is affected similarly by the omission of 

residential gas heating emissions, but only by 5% of a relatively 

small total emissions inventory (see Table 12). Although the 

submitted VOC emissions inventory shows the largest number of 

unreported source categories and under-estimated emissions, the 

amount of omitted emission estimates is mostly offset by the more 

accurate on-road mobile VOC emissions estimates, i.e., compare 

the 142.2 tons per year under-report (see Table 10) to a 99.7

tons per year increase supported by ADEQ’s use of Santa Cruz 

County specific data within MOVES (see discussion in section 

4.2.2.1).11 

To conclude, we find that PM2.5, NH3, NOx, and SO2, four of 

 

11 See Table 1 for the 150.8 ton difference in the submitted Santa Cruz County 

on-road mobile VOC emissions estimate and the similar 2008 NEI version 3.0 

emissions estimate. These additional 150.8 tons are allocated to the Nogales

nonattainment area according to population share (0.661) providing a source 

category emissions estimate adjustment of 99.7 tons per year. For reference, 

the VOC estimates in Table 12 incorporate this adjustment. 
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Technical Support Document for Proposed Rule, Docket EPA-R09-OAR-2014-0450

five emissions inventories, show little or no variance as derived 

from our reference emissions inventory, the 2008 NEI version 3.0 

emissions inventory. As described above, the total VOC emissions 

inventory, considering its omitted source categories, shows a 

small overall difference of 3 - 10 percent when compared to 

either the 2008 NEI version 3.0 Santa Cruz County baseline 

emissions inventory, or to the Nogales nonattainment area 

calculations. We consider this variance to be small in the 

context of the overall PM2.5 emissions inventories. Consequently, 

we are proposing to find that Arizona’s submitted 2008 and 2010 

PM2.5, NH3, NOx, SO2, and VOC emissions inventories meet the CAA 

section 172(c)(3) requirement to provide a comprehensive, 

accurate, and current inventory of actual emissions for the 

Nogales PM2.5 nonattainment area.