Technical Memorandum 

To: Mobile Sources Forum 

From: Tom Moore, Technical Coordinator 

Date: November 26, 2002 

Subject: 

 

Summary and Discussion of 1996 through 2018 Mobile Source Emissions 

Inventories 

Introduction

At the direction of the WRAP Mobile Sources Forum (MSF), as part of the requirements of §309 of 

the Regional Haze Rule, emissions inventories of mobile source and road dust emissions were 

prepared for the 9-state region of the Grand Canyon Visibility Transport Commission (GCVTC). 

These annual inventories covered the time period 1996 through 2018, inventorying 1996, and then 

projecting 2003, 2008, 2013, and 2018. The projections assumed and included all on-road mobile 

source control programs “on the books” as of 2001, and all off-road control programs “on the books” 

as of mid-2000. Mobile source control programs proposed or under consideration were not included in 

the projections, nor were off-road recreational equipment controls finalized in September 2002. 

Mobile source emissions have been defined by the MSF as tailpipe, evaporative, and tire and brake 

wear emissions from on-road and non-road mobile sources. Use of the terms “off-road” and “nonroad” is interchangeable in the air quality regulatory sector, and in this memo as well. Road dust 

emissions have been defined by the MSF as re-entrained roadway fugitive dust emissions from on-road 

mobile sources. The focus of this memo is mobile source emissions. 

WRAP used and followed the appropriate EPA guidance, or the more recent EPA methodologies used 

in NEI99, to develop the mobile source emission inventories. These inventories were developed 

during 2001-02 by ENVIRON, Pechan, and Sierra Research under a WRAP contract to ENVIRON 

(ENVIRON et. al., 2002). For on-road emissions estimates, EPA guidance is to use the MOBILE6 and 

PART5 emissions models for grams/mile emission factors, and highway performance monitoring 

system (HPMS)-based vehicle miles traveled (VMT) estimates. ENVIRON differed from EPA 

guidance by using a modified version of PART5. ENVIRON used the June 2000 draft NONROAD 

model with EPA knowledge and understanding. For the aircraft, locomotive, and commercial marine 

categories, ENVIRON used current practice similar to what EPA used in the NEI99, in the absence of 

up-to-date EPA guidance documents for non-road emission inventory development. WRAP prepared 

these inventories to comply with the §309 requirements from the Regional Haze Rule; the need for 

these inventories was recommended by the GCVTC in its 1996 report (GCVTC, 1996; and EPA, 

Federal Register, 40 CFR Part 51, 1999). States and tribes in the GCVTC region are eligible to 

prepare regional haze implementation plans under §309; that geographic area includes the states of 

Arizona, California, Colorado, Idaho, Nevada, New Mexico, Oregon, Utah, and Wyoming. 
2

1. Recommended Areas for Analysis

The MSF has identified up to 13 urban areas and California for separate analysis and evaluation as to 

the effect of mobile source emissions on the 16 Class I areas covered by §309 and the GCVTC. Based 

on the intent of the GCVTC and the preamble to the Regional Haze Rule, the MSF recommends that 

the effect of mobile source emissions from the metropolitan statistical areas (MSA) in the 9-state 

GCVTC region with populations greater than 250,000, be evaluated (WRAP MSF, 2002a). The MSF 

also recommended that the effect of mobile source emissions first be examined separately on a 

cumulative basis for emissions from the 9-state GCVTC region and California. Mobile source 

emissions from the 9-state GCVTC region, California, the Phoenix-Mesa, AZ MSA, and the Las 

Vegas, NV MSA were selected jointly by the MSF and the WRAP Air Quality Modeling Forum for 

modeling simulations of the no mobile source emissions tests defined by the MSF. In the case of the 

Phoenix-Mesa and Las Vegas MSAs, the mobile source emissions from Maricopa and Clark Counties, 

respectively, were selected to represent those urban areas, as those counties comprise the vast majority 

of each MSA’s population and urban land-use area, and associated mobile source emissions (WRAP, 

2002b). 

2. Issues with Including Tribal Reservation Lands in the Definition of Urban Areas

The use of MSA boundaries as the WRAP definition of urban area requires some clarification with 

respect to mobile source emissions from tribal lands within an MSA. EPA has proposed to use MSA 

(here the more inclusive term Consolidated Metropolitan Statistical Area, or CMSA, is used) 

boundaries as the presumptive boundaries for nonattainment area designations required over the next 

few years. Tribes having portions of their reservations within CMSA boundaries have objected to the 

EPA approach for these presumptive nonattainment boundaries, both on tribal sovereignty grounds, 

and because these tribes may not be socially and economically integrated into the CMSA. As a matter 

of law, State Implementation Plans (SIP) do not apply to lands under tribal jurisdiction, absent special 

circumstances. Thus, even as the individual urban area definition for WRAP Mobile Source emissions 

finding may utilize the CMSA boundaries, the state’s mobile source emissions budget (in a case where 

significant impact is found) under a §309 SIP, would not apply to any tribal area within a given 

CMSA. If a significant impact were found by WRAP, any tribal mobile source emissions budget 

would be implemented through a tribal or federal implementation plan (TIP or FIP). 

3. Qualification Statements for Use of Data from the Mobile Source Emissions Inventories

The predicted mobile source emissions inventories should be considered conservative because the nonroad mobile emissions estimates are likely overstated. This is due to the following: 

• EPA expects to release a new NONROAD emissions model soon, that reduces the activity levels 

for many types of non-road equipment, and is estimated to reduce the level of emissions compared 

to the current NONROAD model by 25 to 50%; and 

• With the exception of California and Phoenix, use of high sulfur diesel fuel (~3,000 to 4,000 ppm 

S) was assumed in the WRAP non-road mobile emissions inventory as specified in current 

regulations. EPA is likely to promulgate new emissions standards for large non-road diesel 

engines along with requirements for lower non-road diesel sulfur levels.
3

4. Emissions Summary for Geographic Areas in the 9-state GCVTC Region

Table 1 summarizes the 2018 air quality modeling Base Case annual anthropogenic emissions by 

major source category in the 9 GCVTC states. Mobile source emissions (on-road plus non-road) are a 

major contributor to the total anthropogenic NOx (47%) and SO2 (21%) emissions, as well as 

contributing significant amounts of ammonia (8%) and fine particulate (12%). The non-road mobile 

source category contributes a majority of the total mobile source NOx (64%), SO2 (97%), and fine 

particulate (83%) emissions. Thus, non-road mobile emissions will be responsible for the majority of 

the total mobile source emissions’ impacts on visibility. 

Table 1. Summary of annual emissions in tons per year (tpy) in the 9 GCVTC states by major source 

category for the 2018 air quality modeling Base Case emissions scenario. 

 NOX SO2 NH3 PM2.5

 (tpy) % (tpy) % (tpy) % (tpy) % 

Area 377,833 16% 74,697 8% 594,764 87% 352,437 57% 

Road Dust 0 0% 0 0% 0 0% 66,470 11% 

Point 885,720 37% 642,133 72% 30,218 4% 127,374 21% 

Mobile 407,691 17% 5,426 1% 57,326 8% 12,259 2% 

Non-Road 700,271 30% 175,343 20% 3,398 0% 61,131 10% 

Total 2,371,515 100% 897,599 100% 685,706 100% 619,671 100% 

On-road mobile source emissions trends are downward from 1996 to 2018, in individual urban areas, 

each GCVTC state, and across the 9-state region. Non-road mobile source emissions trends for 1996 

to 2018 vary by urban area and state. For example, NOx dominates the Nevada non-road mobile 

source emissions inventory, and construction equipment is the largest portion of those NOx emissions. 

ENVIRON used state-specific growth rates, and Nevada has the greatest construction growth rate. 

From 1996 to 2003, growth is larger than the effects of new standards in Nevada. From 2003 to 2013, 

when there is fleet turnover from new standards, the effects of the new standards are larger than the 

growth rates. By 2018, much of the fleet has turned over, and the growth effect is again larger. 

Similar things are going on in the other areas where you see non-monotonic trends. This is apparent in 

some of the urban area tables and plots as well (e.g., Clark County, NV). 

5. Mobile Source Emissions Data Tables – Geographic Areas

Tables 2 through 4 display the mobile source emissions inventory data for the GCVTC 9-state region, 

for the 1996 through 2018 time frame. These tables are organized into total mobile source emissions, 

on-road mobile source emissions, and non-road mobile source emissions. Tables 5 through 31 display 

the mobile source emissions inventory data for selected individual urban areas in alphabetical order, in 

the GCVTC 9-state region, of the 13 MSA populations greater than 250,000 persons outside 

California, for the 1996 through 2018 time frame. These tables are grouped into total mobile source 

emissions, on-road mobile source emissions, and non-road mobile source emissions. VOC, NOx, SO2, 

and PM10 emissions from individual urban areas are expressed in annual average tons. Tables 32 

through 58 display the mobile source emissions inventory data for each of the 9 states in the GCVTC 

region in alphabetical order, for the 1996 through 2018 time frame. These tables are again grouped 

into total mobile source emissions, on-road mobile source emissions, and non-road mobile source 

emissions. VOC, NOx, SO2, and PM10 emissions from the 9 individual states are again expressed in 

annual average tons. 
4

Table 2. Total Mobile Source emissions by GCVTC state (total annual daily averages of tons of VOC, 

NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
5

Table 3. On-Road Mobile Source emissions by GCVTC state (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
6

Table 4. Non-Road Mobile Source emissions by GCVTC state (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
7

Table 5. Total Mobile Source emissions in the Albuquerque, NM urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
8

Table 6. On-Road Mobile Source emissions in the Albuquerque, NM urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
9

Table 7. Non-Road Mobile Source emissions in the Albuquerque, NM urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
10

Table 8. Total Mobile Source emissions in the Colorado Springs, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
11

Table 9. On-Road Mobile Source emissions in the Colorado Springs, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
12

Table10. Non-Road Mobile Source emissions in the Colorado Springs CO urban area (total annual 

daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018. 
13

Table 11. Total Mobile Source emissions in the Denver, CO urban area (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
14

Table 12. On-Road Mobile Source emissions in the Denver, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
15

Table 13. Non-Road Mobile Source emissions in the Denver, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
16

Table 14. Total Mobile Source emissions in the Fort Collins, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
17

Table 15. On-Road Mobile Source emissions in the Fort Collins, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
18

Table 16. Non-Road Mobile Source emissions in the Fort Collins, CO urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
19

Table 17. Total Mobile Source emissions in the Las Vegas, NV urban area (Clark County) (total 

annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
20

Table 18. On-Road Mobile Source emissions in the Las Vegas, NV urban area (Clark County) (total 

annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
21

Table 19. Non-Road Mobile Source emissions in the Las Vegas, NV urban area (Clark County) (total 

annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
22

Table 20. Total Mobile Source emissions in the Phoenix, AZ urban area (Maricopa County) (total 

annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018. 
23

Table 21. On-Road Mobile Source emissions in the Phoenix, AZ urban area (Maricopa County) (total 

annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
24

Table 22. Non-Road Mobile Source emissions in the Phoenix, AZ urban area (Maricopa County)

(total annual daily averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 

2018.
25

Table 23. Total Mobile Source emissions in the Provo, UT urban area (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
26

Table 24. On-Road Mobile Source emissions in the Provo, UT urban area (total annual daily averages 

of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018. 
27

Table 25. Non-Road Mobile Source emissions in the Provo, UT urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018. 
28

Table 26. Total Mobile Source emissions in the Salt Lake City, UT urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
29

Table 27. On-Road Mobile Source emissions in the Salt Lake City, UT urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
30

Table 28. Non-Road Mobile Source emissions in the Salt Lake City, UT urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
31

Table 29. Total Mobile Source emissions in the Tucson, AZ urban area (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
32

Table 30. On-Road Mobile Source emissions in the Tucson, AZ urban area (total annual daily averages 

of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
33

Table 31. Non-Road Mobile Source emissions in the Tucson, AZ urban area (total annual daily 

averages of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
34

Table 32. Total Mobile Source emissions in the State of Arizona (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
35

Table 33. On-Road Mobile Source emissions in the State of Arizona (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
36

Table 34. Non-Road Mobile Source emissions in the State of Arizona (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
37

Table 35. Total Mobile Source emissions in the State of California (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
38

Table 36. On-Road Mobile Source emissions in the State of California (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
39

Table 37. Non-Road Mobile Source emissions in the State of California (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
40

Table 38. Total Mobile Source emissions in the State of Colorado (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
41

Table 39. On-Road Mobile Source emissions in the State of Colorado (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
42

Table 40. Non-Road Mobile Source emissions in the State of Colorado (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
43

Table 41. Total Mobile Source emissions in the State of Idaho (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
44

Table 42. On-Road Mobile Source emissions in the State of Idaho (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
45

Table 43. Non-Road Mobile Source emissions in the State of Idaho (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
46

Table 44. Total Mobile Source emissions in the State of Nevada (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
47

Table 45. On-Road Mobile Source emissions in the State of Nevada (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
48

Table 46. Non-Road Mobile Source emissions in the State of Nevada (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
49

Table 47. Total Mobile Source emissions in the State of New Mexico (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
50

Table 48. On-Road Mobile Source emissions in the State of New Mexico (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
51

Table 49. Non-Road Mobile Source emissions in the State of New Mexico (total annual daily averages 

of tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
52

Table 50. Total Mobile Source emissions in the State of Oregon (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
53

Table 51. On-Road Mobile Source emissions in the State of Oregon (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
54

Table 52. Non-Road Mobile Source emissions in the State of Oregon (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
55

Table 53. Total Mobile Source emissions in the State of Utah (total annual daily averages of tons of 

VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
56

Table 54. On-Road Mobile Source emissions in the State of Utah (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
57

Table 55. Non-Road Mobile Source emissions in the State of Utah (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
58

Table 56. Total Mobile Source emissions in the State of Wyoming (total annual daily averages of tons 

of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
59

Table 57. On-Road Mobile Source emissions in the State of Wyoming (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
60

Table 58. Non-Road Mobile Source emissions in the State of Wyoming (total annual daily averages of 

tons of VOC, NOx, SO2, and PM10), for 1996, 2003, 2008, 2013, and 2018.
61

References 

ENVIRON International Corporation, E.H. Pechan & Associates, Inc., and Sierra Research. 2002. 

“Development Of Wrap Mobile Source Emission Inventories”. Novato, CA. December. 

Federal Register. 1999. 40 CFR, Part 51. Regional Haze Regulations, Final Rule. Vol. 64, No. 126. 

July 1. 

Grand Canyon Visibility Transport Commission. 1996. Final Recommendations Report. June. 

Grantham, Bill. 2002. Personal communication. National Tribal Environmental Council. 

Albuquerque, NM. November 5. 

Pollack, Alison K. 2002. Personal communication. ENVIRON International Corporation. 

Novato, CA. November 25. 

WRAP MSF. 2002a. “Preliminary Recommendations from the WRAP Mobile Sources Forum 

For Defining ‘Significant Impact’ from Mobile Sources/Road Dust for the Purposes of 

Section 309 of the Regional Haze Rule. Western Regional Air Partnership, Mobile 

Sources Forum. June 10. 

WRAP. 2002b. “Phoenix and Las Vegas MSAs – Definition of Urban Area for ‘Zeroing’ of 

Mobile Source Emissions”. Western Regional Air Partnership. August 21.