Appendix F: Paved and Unpaved Road Dust 

1996 and 2018 Inventories for Re-entrained Road Dust From Paved and Unpaved Roads 

Paved and unpaved road dust emissions in the WRAP states were estimated to determine if road 

dust has an effect on visibility in each of the 16 Colorado Plateau Class I areas. In brief, paved 

road dust emissions were estimated using the standard EPA approach, while unpaved road dust 

emissions were estimated using revised silt contents, revised activity data, and transport 

fractions. Paved and unpaved road dust PM10 and PM2.5 emissions by state for 1996 and 2018

are provided in Tables 45 and 46. Paved road dust emissions increase by about three percent per 

year from 1996 to 2018, per the increase in vehicle miles traveled. The increase varies by state, 

with the largest projected growth in vehicle travel in Washington, Idaho, and Utah. Unpaved 

road dust emissions are projected to decrease between 1996 and 2018, by about 0.75% per year, 

because of reductions in unpaved road mileage over time as more roads are paved. As a result,

unpaved road dust emissions are about 80% of road dust PM10 emissions in 1996, and about 65% 

of road dust PM10 emissions in 2018. Overall, road dust PM10 emissions increase by about 6% 

from 1996 to 2018. 

Table 45: 1996 WRAP States Fugitive Road Dust Emissions (TPY) 

State Paved Road Dust Unpaved Road Dust Total Road Dust 

PM10 PM2.5 PM10 PM2.5 PM10 PM2.5

Arizona * 7,318 1,830 18,605 2,791 25,923 4,620

California * 35,643 8,911 86,474 14,090 122,117 23,001

Colorado * 7,897 1,974 30,601 4,590 38,498 6,564

Idaho * 3,502 876 28,304 4,246 31,806 5,121 

Montana 2,909 727 15,796 2,369 18,705 3,097

Nevada * 2,528 632 9,460 1,449 11,988 2,081 

New Mexico * 5,395 1,349 27,972 4,196 33,367 5,545

North Dakota 2,461 615 34,419 5,163 36,880 5,778 

Oregon * 8,067 2,017 19,078 2,862 27,144 4,878

South Dakota 2,296 574 46,199 6,930 48,495 7,504 

Utah * 3,680 920 16,040 2,406 19,721 3,326 

Washington 7,804 1,951 34,365 5,155 42,169 7,106

Wyoming * 1,823 456 3,449 517 5,271 973

13 states total 91,322 22,831 370,762 56,763 462,084 79,594 

* 9 GCVTC States 75,853 18,963 239,983 37,146 315,835 56,109 

NM Regional Haze SIP Page F-1 

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Table 46: 2018 WRAP States Fugitive Road Dust Emissions (TPY) 

State Paved Road Dust Unpaved Road Dust Total Road Dust 

PM10 PM2.5 PM10 PM2.5 PM10 PM2.5

Arizona * 12,618 3,154 12,976 1,945 25,594 5,099

California * 59,794 14,950 56,447 9,198 116,242 24,148

Colorado * 13,771 3,442 36,956 5,544 50,728 8,986

Idaho * 7,548 1,887 17,976 2,697 25,524 4,584

Montana 4,796 1,201 17,907 2,686 22,703 3,887

Nevada * 5,019 1,256 7,198 1,102 12,217 2,358

New Mexico * 10,198 2,551 32,730 4,909 42,928 7,461

North Dakota 3,723 931 34,255 5,139 37,978 6,070 

Oregon * 14,684 3,672 12,158 1,825 26,842 5,497

South Dakota 3,723 931 50,239 7,537 53,962 8,468 

Utah * 7,541 1,883 20,487 3,073 28,028 4,957

Washington 18,681 4,668 22,991 3,449 41,672 8,118

Wyoming * 3,019 756 3,719 558 6,738 1,314

13 states total 165,115 41,282 326,040 49,666 491,155 90,947

* 9 GCVTC States 134,192 33,551 200,648 30,853 334,840 64,404 

Road Dust significance analysis and finding for the Colorado Plateau 16 Class I areas 

Section 309 of the Regional Haze Rule requires the following for Road Dust: 

Area sources of dust emissions from paved and unpaved roads. The plan must include an 

assessment of the impact of dust emissions from paved and unpaved roads on visibility 

conditions in the 16 Class I Areas. If such dust emissions are determined to be a 

significant contributor to visibility impairment in the 16 Class I areas, the State must 

implement emissions management strategies to address the impact as necessary and 

appropriate.

As described above, road dust emissions inventories were developed, and the significance of 

road dust was then tested using the regional air quality model at the Regional Modeling Center. 

The modeling results are presented in Table 47, below. 

NM Regional Haze SIP Page F-2 

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NM Regional Haze SIP Page F-3 

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Table 47: Road Dust Significance Modeling Results 

Colorado Plateau 

Class I Areas 

2018 

Base 

Case 

(Mm-1) 

2018 

No Road 

Dust 

(Mm-1) 

EPA Natural 

Conditions 

Worst 20% Days 

(Mm-1) 

Bext change 

No Road Dust

(Mm-1) 

Bext change 

No Road Dust 

(%) 

dv Change 

No Road Dust 

(dv) 

Arches NP 25.91 25.63 20.12 0.29 1.42 0.14 

Black Canyon of 

Gunnison NP 32.84 32.20 20.26 0.63 3.13 0.31 

Bryce Canyon NP 24.24 23.99 20.12 0.25 1.24 0.12 

Canyonlands NP 23.89 23.71 20.08 0.18 0.89 0.09 

Capitol Reef NP 25.56 25.30 20.18 0.26 1.29 0.13 

Flat Tops Wilderness 28.55 28.37 20.28 0.19 0.92 0.09 

Grand Canyon NP 27.78 27.53 20.08 0.25 1.22 0.12 

Maroon BellsSnowmass Wilderness 31.78 31.46 20.30 0.32 1.57 0.16 

Mesa Verde NP 34.47 34.21 20.18 0.26 1.30 0.13 

Mount Baldy 

Wilderness 41.63 41.26 20.04 0.37 1.87 0.19 

Petrified Forest NP 32.46 32.22 20.08 0.24 1.20 0.12 

San Pedro Parks 

Wilderness 28.90 28.65 20.18 0.24 1.21 0.12 

Sycamore Canyon 

Wilderness 35.34 34.95 20.34 0.39 1.92 0.19 

West Elk Wilderness 31.15 30.85 20.26 0.30 1.47 0.15 

Weminuche Wilderness 29.93 29.77 20.20 0.16 0.80 0.08 

Zion NP 25.57 24.95 20.06 0.61 3.05 0.30 

In the regional model, the road dust inventory was set to zero for the entire modeling domain, 

other 2018 base case emissions were included as normal, and the resulting modeled effect of 

road dust emissions were calculated in terms of the impact on visibility at each of the 16 

Colorado Plateau Class I areas, on the predicted worst 20% days. The modeled regional impact 

of road dust emissions ranged from 0.31 deciviews (3.1% of natural conditions to be reached by 

2064) at the Black Canyon of the Gunnison National Park to 0.08 deciviews (0.8% of natural 

conditions to be reached by 2064) at the Weminuche Wilderness. These data were presented and 

discussed by WRAP’s Modeling and Mobile Sources Forums, the Oversight Committees, and 

the Board of Directors, and all agreed that the regional impacts of road dust emissions are not 

significant at the 16 Colorado Plateau Class I areas at this time. 

The Board of Directors directed the Technical Forums to continue to track and evaluate road dust 

emissions, as dust aerosols have been shown to be an important contributor to visibility 

impairment at many WRAP region Class I areas. The finding of no significance is a rigorous 

test, as no windblown dust emissions are included in the model, so the modeled significance of 

road dust is not masked by a large mass of other dust emissions.