1 

ARIZONA DEPARTMENT OF ENVIRONMENTAL QUALITY 

Payson Update using MOVES 

November 8, 2013 

The Payson Limited Maintenance Plan (LMP) update submitted to EPA January, 2012, contained 

Exhaust, Tire and Brake PM10 emission estimates using the EPA NMIM (Mobile6.2) model. Table 3, 

from that document, summarizing these emissions estimates, is shown below: 

(Table 3: Yearly VMT, and PM10 Vehicular Emissions in 2007 in Payson PM10 Non-Attainment 

Area) 

Roadway Name or 

Roadway Class 

Yearly VMT 

(2007) 

Fugitive 

Dust PM10

(tpy) 

Tire, Exhaust, 

& Brake PM10

(tpy) 

Paved Roads 

SR-87 65,046,464 54.29 5.73 

SR-260 27,448,297 22.91 2.10 

Urban Minor Arterial 16,331,967 13.63 1.00 

Rural Major Collector 5,160,532 4.31 0.34 

Urban Collector 4,378,434 3.65 0.26 

Urban Local 438,915 0.37 0.03 

Rural Minor Collector 196,747 0.16 0.01 

Total Paved 119,001,356 99.33 9.47 

Unpaved Roads 

Rural Local 514,549 105.10 0.03 

Total Unpaved 514,549 105.10 0.03 

Total PM10 emissions 119,515,905 204.43 9.50 

 *: tpy: tons per year 

ADEQ was asked by EPA to recalculate emission estimates for exhaust, tire, and brake wear using the 

MOVES model. To establish reasonable MOVES data, MOVES was run for Gila County with the default 

model values for both 2008 and 2011 and then compared to the EPA generated MOVES runs reported in 

the 2008 and 2011 NEI on-road emission inventory (using MOVES). The NEI total tons per year of onroad PM10 was larger than the value obtained from running MOVES itself. ADEQ contacted EPA about 

the discrepancy, and David Brzezinski (EPA OTAQ ASD) indicated “The default values in 

MOVES2010b do not (and cannot) reflect all of the information we have about counties. When we do the 

NEI, we use county specific databases (CDBs) that contain much more of the information we have about 

counties, both information from states and our own estimates. The data we used can be obtained on the 

EPA web site for the 2008 and 2011 NEI.” Given the indication from EPA regarding the specificity of 

data used to construct the NEI, ADEQ determined that using the emission estimates from the NEI were 

likely more accurate than the default MOVES model runs. 

The tons per year on-road emissions data from the 2008 and 2011 NEI are shown in Table 1. Due to 

differences in model inputs and outputs between NMIM and MOVES, a breakdown of the roadway 

classes that was originally provided in the Payson maintenance plan (Table 3) was not possible for the

more recent MOVES data obtained through the NEI. Instead, an emission factor of grams/VMT 

(gm/vmt) was calculated for each of the NEI years using the total emissions and VMT estimates. 
2 

The default VMT EPA used for the county-level emission estimates in the NEI is from the Highway 

Performance Monitoring System (HPMS). For this analysis, ADEQ also used HPMS data from the 

Arizona Department of Transportation (ADOT). 

Table 1: Annual MOVES / NEI Mobile Source Emissions Estimates, Gila County Annual VMT, 

and resultant MOVES / NEI emission factors

NEI Year Gila County Yearly VMT Total PM10 Mobile Emissions (tpy) 

Gila County gm/vmt 

2008** 814,680,000 56 0.082 

2011*** 621,595,000 45 0.066 

** http://www.azdot.gov/docs/default-source/planning/dvmt-2008.pdf?sfvrsn=2 

*** http://www.azdot.gov/docs/default-source/planning/dvmt-2011.pdf?sfvrsn=6 

The emission factors that were calculated in Table 1 were then linearly interpolated to 2007 to obtain a 

2007 emission factor which could then be applied to the 2007 VMT data from the Payson NA. The 

calculation for this interpolation method is provided below: 

The extrapolation is as follows: 

A = 0.0657 gm/vmt for 2011 

B = 0.0820 gm/vmt for 2008 

C = (A – B) / 3 = - 0.005 gm/vmt change in emission factor per year 

D = B – C = 0.082 + 0.005 = 0.087 gm/vmt emission factor for 2007 

Using the 2007 interpolated MOVES / NEI mobile source emission factor and the 2007 VMT estimates 

from table 3, PM10 emissions from exhaust, tire, and brake were estimated for the Payson NA. A 

comparison of the emission estimates using NMIM (Mobile 6.2) and MOVES / NEI is provided below in 

Table 2. 

Table 2 Comparison of Mobile Emission Estimates using Mobile 6.2 and MOVES 

Mobile Source 

Model 

Emission 

Factor 

(gm/vmt) 

Payson NA 

VMT 

Total Tire, 

Exhaust, & 

Brake PM10 

Emissions (tpy) 

Fugitive 

Dust PM10 

Emissions 

(tpy) 

Total 

Mobile 

PM10

Emissions 

NMIM (Mobile 6.2) 0.072 119,515,905 9.50 204.43 213.93 

MOVES / NEI 0.087 119,515,905 11.52 204.43 215.95 

As a result of this analysis, there was a change of +2.02 tons per year in total on-road PM10 emissions as a 

result of going from the Mobile6.2 results to the MOVES results, thus only a small (+1.0%) change in the 

Payson Area Motor Vehicle Growth Analysis adding 0.1 μg/m3

 to the Motor Vehicle Regional Analysis 

value. 
3 

(From the “2011 Update of the Limited Maintenance Plan for the Payson PM10 Maintenance Area” we 

have Figure 4.2, a computation of the Payson Area Motor Vehicle Growth Analysis and how it relates to 

the MOS.) 

(Figure 4.2 Revised Payson Area Motor Vehicle Growth Analysis) 

DV + (VMTpi ∗ DVmv) < MOS 

Where: 

 DV = the area’s design value based on the most recent 5 years of quality 

assured data in μg/m3

 VMTpi = the projected percentage increase in VMT over the next ten years1

 DVmv = motor vehicle design value based on on-road mobile portion of the 

attainment year inventory in μg/m3

 MOS = margin of safety for the relevant PM10 standard for a given area: 98 

μg/m3 for the 24-hour standard 

Applying the test for the 24-hour average PM10 standard yields the following result: 

 DV = 66 μg/m3

 VMTpi = 23.8 percent 

 DVmv = 40.9 μg/m3 (estimated using the PM10 emissions in Table 4-1) 

 MOS = 98 μg/m3 for 24-hour average PM10 standard 

66 + (0.238 ∗ 40.9) = 75.7 μg/m3

Because the Motor Vehicle Regional Analysis is less than 98 μg/m3, the area continues to pass this 

criterion for the 24-hour average PM10 standard. 

 

1 Based on a trend analysis of the most recent 10 years of HPMS data, ADEQ calculated an increase in VMT to be 

approximately 20,000,000 per year or 200,000,000 over a 10 year period for Gila County. Based on an annual VMT 

of 840,000,000 for the county in 2008 it represents an increase of 23.8%. The same percentage (23.8%) is applied 

for the Payson VMT growth projection.