Technical Support Document

Regional Haze State Implementation Plan 

Analysis of Colorado visibility impacts on nearby Class I Areas 

October 2008 Revision 

Colorado Visibility Impacts on nearby Class I Areas 1 of 19
The below map (Figure 1), depicts the western and midwestern IMPROVE monitor locations 

that are identified by small circles. Each IMPROVE monitor is typically sited near a Class I Area 

(CIA) that may represent one or more nearby CIAs. The IMPROVE monitor locations denoted 

with a red dot and four letter abbreviations were evaluated for Colorado impacts since they are 

the closest areas surrounding Colorado. An informal review of PSAT data for more distance 

IMPROVE monitors (identified by gold circles) indicated minimal or non-existent Colorado 

impacts. 

Figure 1: Class I Areas of the Central and Western United States 

The below listed PSAT modeling summary tables for sulfate (Table 1) and nitrate (Table 2) 

indicate the Colorado visibility impacts in percent and the relative rank. For purposes of 

identifying Colorado visibility impacts that may be of concern to surrounding States, the Division 

proposes a threshold criterion to include ≥ 5.0% or a ranking in the top 5 among source regions. 

In the below tables, all Colorado visibility impacts satisfying these criterion are shaded in purple. 

Any future (2018) visibility impact from Colorado that is over 10% is indentified in orange and is 

considered as significant. 

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Table 1: PM Source Apportionment Technology (PSAT) Modeling Results for Sulfate 

Table 2: PM Source Apportionment Technology (PSAT) Modeling Results for Nitrate 

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For Arkansas, the Colorado visibility impacts were evaluated for the closest CIA – Upper Buffalo 

Wilderness (UPBU). The single largest Colorado visibility impact identified is 1.2% for nitrate on 

the worst days in 2018. This level of impact is not considered to a significant contributor to 

visibility degradation thus the Division has determined that no further evaluation of the 

remaining Arkansas Class I areas is necessary considering the relative distance from Colorado. 

For Arizona, the Colorado visibility impacts were evaluated on the three nearest Class I areas 

including Petrified Forest National Park (PEFO), Sycamore Canyon Wilderness Area (SYCA) 

and Grand Canyon National Park (GRCA). The single largest Colorado visibility impact 

identified (1.6% nitrate) occurs at SYCA in 2018. This level of impact is not considered a 

significant contributor to visibility degradation thus the Division has determined that no further 

evaluation of the remaining Arizona Class I areas is necessary considering the relative distance 

from Colorado. 

For Missouri, the Colorado visibility impacts were evaluated for the closest CIA – HerculesGlade Wilderness (HEGL). The single largest Colorado visibility impact identified is 1.7% for 

nitrate on the best days in 2018. This level of impact is not considered to a significant 

contributor to visibility degradation thus the Division has determined that no further evaluation of 

the remaining Missouri Class I areas is necessary considering the relative distance from 

Colorado. 

For New Mexico, the Colorado visibility impacts were evaluated for the four nearest Class I 

areas with PSAT modeling. The single largest Colorado visibility impact identified (12.9% 

nitrate) occurs at WHPE in 2018. The WHPE site represents both Wheeler Peak & Pecos 

Wilderness Areas. This level of impact exceeds the informal criteria for triggering further 

interstate consultation. Consequently, the Division will consult further with New Mexico on 

Colorado visibility impacts on Wheeler Peak and Pecos Wilderness Areas. All other 2018 

Colorado visibility impacts on other two nearby New Mexico Class I Areas are under 7.5% which 

are deemed to be a concern that will be addressed in the WHPE consultation process with New 

Mexico. 

For Oklahoma, the Colorado visibility impacts were evaluated for the only CIA – Wichita 

Mountains National Wildlife Refuge Wilderness (WIMO). The largest Colorado visibility impacts 

identified are 5.7% & 5.4% for nitrate on the best days in 2002 & 2018 respectively. These 

visibility impacts exceed the “concern” threshold criterion. 

For South Dakota, the Colorado visibility impacts were evaluated for both Class I areas – Wind 

Cave National Park (WICA) and Badlands National Park (BADL). The WICA site experiences a 

Colorado visibility impact exceeding the threshold criteria for nitrate on the worst days in 2002 

but this impact appears to be mitigated based on the PSAT model projections for 2018. Thus 

the Division has determined that no further technical evaluation of Colorado visibility impacts is 

necessary. 

For Utah, the Colorado visibility impact was evaluated for the nearest Class I areas – 

Canyonlands National Park (CANY) and Capital Reef National Park (CAPI). Looking at the 

PSAT analysis for the CANY site, Colorado has visibility impacts exceeding the “concern” 

threshold criterion for nitrate on the best (4.1% in 2018) and worst days (6.9% in 2018). No 

visibility impacts of “concern” are identified for the CAPI Class I area. 

For Wyoming, the Colorado visibility impact was evaluated for the nearest Class I area - Bridger 

Wilderness (BRID). The single largest Colorado visibility impact identified (0.7% sulfate) occurs 

on the worst days at BRID in 2002. This level of impact is not considered to a significant 

contributor to visibility degradation thus the Division has determined that no further evaluation of 

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the remaining Wyoming Class I areas is necessary considering the relative distance from 

Colorado. 

In summary, the Division has identified 2018 nitrate visibility impacts at Wheeler Peak (WHPE) 

Wilderness Area that trigger interstate consultation with New Mexico. Also, Colorado nitrate 

impacts are of concern at two other nearby New Mexico Class I areas (BAND & SAPE), 

Canyonlands National Park (CANY) in Utah, and Wichita Mountains NWR Wilderness in 

Oklahoma. The “concern” visibility impacts are at or slightly above the arbitrary threshold 

criteria established by the Division. The Western Regional Air Partnership (WRAP) 

Implementation Working Group (IWG) has not formally established threshold criteria on 

interstate Class I area impacts but an informal threshold of 10% has been suggested among 

member states. If the Division were to utilize the informal threshold criteria of the WRAP IWG, 

Colorado would have only one 2018 visibility impact on two nearby Class I areas exceeding the 

10% threshold. 

Colorado Visibility Impacts on nearby Class I Areas 5 of 19
COLORADO VISIBILITY IMPACTS ON ARKANSAS

Caney Creek Wilderness (CACR) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.7%; 2018 = 0.6% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.1%; 2018 = 0.1% 

Caney Creek Wilderness (CACR) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 2.1%; 2018 = 2.2% 

Colorado Nitrate Impact on Worst Days: 2002 = 1.1%; 2018 = 1.2% 

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COLORADO VISIBILITY IMPACTS ON ARIZONA

Petrified Forest National Park (PEFO) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.4%; 2018 = 0.2% 

Colorado Sulfate Impact on Worst Days: 2002 = 1.3%; 2018 = 1.0% 

Petrified Forest National Park (PEFO) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 1.3%; 2018 = 1.5% 

Colorado Nitrate Impact on Worst Days: 2002 = 0%; 2018 = 0.9% 

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Grand Canyon National Park (GRCA) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.5%; 2018 = 0.3% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.9 %; 2018 = 0.7% 

Grand Canyon National Park (GRCA) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 1.1%; 2018 = 1.2% 

Colorado Nitrate Impact on Worst Days: 2002 = 0%; 2018 = 0% 

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Sycamore Canyon Wilderness (SYCA) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.3%; 2018 = 0% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.8%; 2018 = 0.5% 

Sycamore Canyon Wilderness (SYCA) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 0.5%; 2018 = 0.6% 

Colorado Nitrate Impact on Worst Days: 2002 = 1.3%; 2018 = 1.6% 

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COLORADO VISIBILITY IMPACTS ON MISSOURI

Hercules-Glade Wilderness (HEGL) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.8%; 2018 = 0.6% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.2%; 2018 = 0.3% 

Hercules-Glade Wilderness (HEGL) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 1.6%; 2018 = 1.7% 

Colorado Nitrate Impact on Worst Days: 2002 = 1.3%; 2018 = 1.6% 

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COLORADO VISIBILITY IMPACTS ON NEW MEXICO

San Pedro Parks Wilderness (SAPE) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 4.3%; 2018 = 3.4% 

Colorado Sulfate Impact on Worst Days: 2002 = 1.4%; 2018 = 1.2% 

San Pedro Parks Wilderness (SAPE) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 7.7%; 2018 = 7.5% 

Colorado Nitrate Impact on Worst Days: 2002 = 2.7%; 2018 = 2.4% 

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Bandelier National Monument (BAND) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 3.3%; 2018 = 2.6% 

Colorado Sulfate Impact on Worst Days: 2002 = 1.4%; 2018 = 1.2% 

Bandelier National Monument (BAND) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 6.4%; 2018 = 6.3% 

Colorado Nitrate Impact on Worst Days: 2002 = 4.8%; 2018 = 5.1% 

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Wheeler Peak & Pecos Wilderness Areas (WHPE) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 11.0%; 2018 = 8.8% 

Colorado Sulfate Impact on Worst Days: 2002 = 3.2%; 2018 = 2.5% 

Wheeler Peak & Pecos Wilderness Areas (WHPE) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 15.3%; 2018 = 12.9% 

Colorado Nitrate Impact on Worst Days: 2002 = 4.5%; 2018 = 3.8% 

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COLORADO VISIBILITY IMPACTS ON OKLAHOMA

Wichita Mountains National Wildlife Refuge (WIMO) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 2.3%; 2018 = 2.0% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.3%; 2018 = 0.3% 

Wichita Mountains National Wildlife Refuge (WIMO) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 5.7%; 2018 = 5.4% 

Colorado Nitrate Impact on Worst Days: 2002 = 0.9%; 2018 = 0.9% 

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COLORADO VISIBILITY IMPACTS ON SOUTH DAKOTA

Wind Cave National Park (WICA) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 1.9%; 2018 = 1.1% 

Colorado Sulfate Impact on Worst Days: 2002 = 3.3%; 2018 = 3.1% 

Wind Cave National Park (WICA) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 2.8%; 2018 = 2.5% 

Colorado Nitrate Impact on Worst Days: 2002 = 5.0%; 2018 = 4.1% 

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Badlands National Park (BADL) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.8%; 2018 = 0.4% 

Colorado Sulfate Impact on Worst Days: 2002 = 2.1%; 2018 = 2.2% 

Badlands National Park (BADL) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 2.8%; 2018 = 2.6% 

Colorado Nitrate Impact on Worst Days: 2002 = 3.0%; 2018 = 2.6% 

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COLORADO VISIBILITY IMPACTS ON UTAH

Canyonlands National Park (CANY) - PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 2.0%; 2018 = 1.2% 

Colorado Sulfate Impact on Worst Days: 2002 = 3.4%; 2018 = 2.3% 

Canyonlands National Park (CANY) - PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 4.6%; 2018 = 4.1% 

Colorado Nitrate Impact on Worst Days: 2002 = 6.9%; 2018 = 6.9% 

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Capital Reef National Park (CAPI)- PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0.3%; 2018 = 0.3% 

Colorado Sulfate Impact on Worst Days: 2002 = 1.0%; 2018 = 0.6% 

Capital Reef National Park (CAPI)- PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 1.4%; 2018 = 1.3% 

Colorado Nitrate Impact on Worst Days: 2002 = 0%; 2018 = 0% 

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COLORADO VISIBILITY IMPACTS ON WYOMING

Bridger & Fitzpatrick Wilderness Areas (BRID)- PSAT Modeling for PS4 (sulfate) 

Colorado Sulfate Impact on Best Days: 2002 = 0%; 2018 = 0% 

Colorado Sulfate Impact on Worst Days: 2002 = 0.7%; 2018 = 0.5% 

Bridger & Fitzpatrick Wilderness Areas (BRID)- PSAT Modeling for PN3 (nitrate) 

Colorado Nitrate Impact on Best Days: 2002 = 0.3%; 2018 = 0.2% 

Colorado Nitrate Impact on Worst Days: 2002 = 0.6%; 2018 = 0% 

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