Appendix A: Projection of Visibility Improvement

Im prove m e nt in visibility for the 16 Colorado Plateau Class I areas was m odeled for two scenarios, th e results of which are sh own in Tables A-1 and A-2 in Section A of this SIP.

Control Strategies

Scenario 1 is designed to assess the effect of the Grand Canyon Visibility Transport Comm ission (GCVTC) recomm ende d control strategies, co mparing the 1996 m o deled base case to the visibility improvem e nt resulting from the im pl em entation o f the f o llow i ng GCVTC str a teg i es : the sulfur dioxide Annex Milest ones, the regional pollution prev ention program , m a intenance of existing base s m oke m a nagem e nt program s, an d accounting for the 2018 base case e m issions (known and adopted federal, trib al, state, and local control pr ogram s in the contiguous WRAP region). Visibility changes re sulting from regional im ple m entation of state pollution prevention

program s were m odeled by the Regional Modeling Center, as part of the other Section 309

contro l str a tegies. Vis i bility chang e s resu lting f r om im plem entation of pollution prevention

program s by individual states or tribes were not modeled. Em issions changes from state or tribal pollution prevention program s, and the resulting visibility changes are sm all, based on the regional pollution preven tion em issio n s analysis, but are acco unted for in the reg i onal modeling.

Scenario 2 is des i gned to assess the effect of the implem entation of enhanced sm oke

m a nage m e nt program s, as refl ected in the W RAP Fire Em is sions Joint Forum ’ s 2018 optim al

sm oke managem e nt inventory. Enhanced sm oke m a nagem e nt program s were recom m e nded by GCVTC and are required in Sectio n 309 of the Re gional Haze Rule. This scenario uses the

em issions inventories from Scenario 1, except the optim al sm oke m a nagem e nt inventory was substituted for fire em is sions. Thus, the result s for Scenario 2 are a com p arison of visibility changes resulting from em ission reductions betw een the 2018 baseline sm oke m a na gem e nt and 2018 optim al sm oke m a nagem e nt fire inventories.

Modeling results projecting visibility improvement in 2018

Visibility at the 16 Class I ar eas on the Colorado Plateau was estim a ted for the 2018 Scenario 1 and Scenario 2 control st rategies. Tables A-1 and A-2 display the improvem e nts in visibility from the 1997-2001 baseline period to 2018 under Scenario 1 and 2 conditions for the, respectively, worst 20% and best 20% visibility days.

On the average 20% w o rst visibility days, projected im provem ent from 1997-2001 to 2018 for Scenario 1 at the 16 Class I areas on the Colorad o Plateau ranges from a m a xi m u m r e duction of 3.89 deciviews at Sycamore Canyon National Park in Arizona to a m a xi m u m increase of 1.42 deciviews at San Pedro Parks W ilderness in New Mexico. On th e wors t 20% d a ys, Scenario 1 shows im proving vis i bilityat half and degrad a ti on in visibility f o r th e othe r ha lf of the 16 Colorado Plateau C l ass I areas. On the average 20% best visibility days, projected change from 1997-2001 to 2018 Scenario 1 ranged from a m a xi m u m r e duction of 2.11 deciviews at Zion National Park in Utah to a m a xi m u m increase of 1.51 deciviews at San Pedro Parks W ilderness Area in New Mexico. On the best20% days, S cenario 1 improves vi sib ility cond itions at thre equarters of the Class I areas on the C o lorado Plateau.

NM Regi onal Haze SIP Page A-1 12/ 31/ 03NM Regional Haze SIP Page A-2 12/31/03 A comparison of the visibility estimates for 2018 Scenarios 1 and 2 at the 16 Class I areas on the Colorado Plateau for the worst 20% (Table A-1) and best 20% (Table A-2) days reveals that 2018 Scenario 2 always estimated improved visibil ity as compared to 2018 Scenario 1. That is, the optimal smoke management programs produces visibility improvement s over the base smoke management programs across all 16 Class I areas for both the worst 20% and best 20% days.