ARIZONA DEPARTMENT 

OF 

ENVIRONMENTAL QUALITY 

11 10 West Washington Street Phoenix, Arizona 85007 

Janice K. Brewer (602) 771 -2300 www.azdeq.gov Henry R. Darwin 

Governor Director 

Deborah Jordan 

Air Director, U.S. EPA Region IX 

75 Hawthorn Street 

Mail Code Air - 1 

San Francisco, CA 94 105 

Re: Arizona Regional Haze State Implementation Plan 

On February 28, 201 1, ADEQ adopted and submitted to the Environmental Protection Agency (EPA), 

Arizona's State Implementation Plan (SIP) for Regional Haze under Section 308 of the Federal Regional 

Haze Rule. EPA has identified approvability issues regarding visibility degradation on best days at two 

IMPROVE monitors. The two monitoring sites are Saguaro NM (SAGUI) and Chiricahua NM (CHIRI). 

The monitor SAGUl represents Saguaro National Park, East Unit and CHIRl represents Chiricahua 

National Monument, Chiricahua Wilderness, and Galiuro Wilderness. ADEQ reviewed visibility 

monitoring data, emissions inventories, and modeling information used for developing the regional haze 

SIP. Based on this review, ADEQ maintains that degradation will not occur at these monitors and offers 

the following explanation in support of approving Arizona's Regional Haze SIP. 

Section 308(d)(l) of the Regional Haze Rule requires that states ensure no degradation in visibility for the 

least impaired (best) days. Visibility projections however, show degradation at two IMPROVE monitors, 

CHIRl and SAGUl . The degradation at the CHIRl and SAGU 1 monitors amounts to 0.03 deciview (dv) 

and 0.1 dv, respectively. According to established literature, the change in deciview that is perceptible to 

the human eye is 0.5 dv. Even though the amount of degradation is very small, ADEQ agrees that it 

needs to be addressed. 

The degradation is a comparison of the 2000-2004 monitored data to the modeled projections using the 

CMAQ model, which is based on a projected 201 8 emission inventory (titled PRP18b) assembled by the 

Western Regional Air Partnership (WRAP). Table I below shows the light extinction from each pollutant 

on the 20% best days for both the 2000-2004 baseline period average and the 2018 projection for the 

Saguaro National Monument (SAGUl), along with the total light extinction and dv impacts. Table 1 also 

includes the 2005-2009 progress average. It should be noted that the total light extinction value includes 

a Rayleigh scattering value of 10 inverse megameters (~m-') (per EPA guidance) which constitutes half 

of the light extinction. Table 2 shows the same information for Chiricahua National Monument (CHIRI). 

Southern Regional Office 

400 West Congress Street Suite 433 Tucson, AZ 85701 

(520) 628-6733 

Prin red on recycled paper 
Page 2 of 5 

Table 1: SAGU 1 Visibilitv Data 

Source: visibility projection link on http://vista.cira.colostate.edu/tss/Results~~ePlanning.aspx 

Table 2: CHIRl Visibilitv Data 

Sulfate 

Nitrate 

Organic Carbon 

1 Sulfate 1 2.3 I 2.3 1 2.1 1 

2.7 

1 .O 

2.2 

1.3 

1.1 

1.8 

0.1 

10 

20 

7 

I 

1 Nitrate 1 0.5 I 0.5 I 0.4 1 

Fine Soil 

Coarse Material 

Sea Salt 

Rayleigh Scattering 

( Organic Carbon I 1.4 1 1.4 I 0.9 1 

2.5 

1 .O 

2.3 

0.9 

1.8 

1.8 

0.1 

10 

20 

7 

Total light extinction 

Total Deciview 

2.8 

0.8 

7 

1 Coarse Material I 1.2 1 1.2 I 1.2 I 

1 Elemental Carbon 

me~oil 

I Sea Salt I 0.0 I 0.0 i 0.1 I 

0.7 

0.3 0.4 

Rayleigh Scattering 

Total light extinction 

These tables differ slightly from what was reported in the proposed Regional Haze State Implementation 

Plan (SIP). The submitted SIP carried the light extinction to two decimal places. In order to maintain the 

appropriate level of significant figures, those numbers have been rounded to one decimal pIace. 

Moreover, in mathematical operations involving significant figures, the final values determined must be 

reported in such a way that it reflects the reliability of the least precise value. According to EPA's 

"Guidance for Tracking Progress Under the Regional Haze Rule" EPA has had a "practice of rounding 

each constant in the aerosol extinction calculation to one significant digit ..." This practice has been 

incorporated into the above tables for the total light extinction calculation. This is particularly appropriate 

Total Deciview 

10 

20 

7 

10 

20 

10 

20 

7 7 
Page 3 of 5 

since the Rayleigh scattering value is only carried to one significant figure. Even if each component had 

been revised to be one significant figure, the resulting total light extinction is the same. Using this 

approach for both SAGU I and CHIRI, the difference between light extinction (and hence visibility) in 

the base 2000-2004 period and projected for 201 8 is zero. 

While the Department maintains that there is no degradation at SAGUl and CHIRl due to the above 

discussion regarding the accuracy of the light extinction values, Table 1 shows that an increase in fine soil 

light extinction is the main reason for the visibility degradation that was reported at SAGUl in the SIP 

submittal. The visibility impacts of all other pollutants are projected to remain constant or decrease, with 

the exception of a small projected increase in organic carbon. However, when these projected values are 

compared to the 2005-2009 progress conditions, it can be seen that the projections are mostly 

conservative, and in fact for fine soil, rather than increasing by approximately 60% as projected, visibility 

impacts decreased during the progress period by about 30%. 

Table 2 shows that an increase in fine soil and sulfate light extinction are the main reasons for the 

visibility degradation that was reported at CHIRl in the SIP submittal. The visibility impacts of all other 

pollutants are projected to remain constant or decrease. However, when these projected values are 

compared to the 2005-2009 progress conditions, it can be seen that the projections are conservative, the 

only exception being sea salt. 

Part of the reason that the projected light extinction values for fine soil are so high is because of 

questionable assumptions regarding fine soil increases. EPA recommended that the 20 18 light extinction 

projection be conducted using relative response factors (RRFs) to predict future monitored values using a 

change in modeled values. The RRFs are defined as the ratio of the modeled 201 8 projections divided by 

the modeled 2002 values. The RRFs are used as multipliers for the 2002 monitored data in order to 

calculate the 2018 "monitored projections" as described in the following equations: 

RRF = Modeled 20 1 8 

Monitored201 8 = Monitored2002 * RRF where Modeled 2002 

Monitored 201 8 = Monitored 2002 * Modeled 201 8 

Modeled 2002 

This means that the RRFs are used to adjust the 2002 monitored data to reflect what would be the 

projected monitored data in 2018. For most PM25 species the REWs were close to one, meaning the 

model predicted fairly consistent impacts from those emissions. However, for fine soil at SAGU 1 on best 

days, the RRF was 1.6, meaning the model projected a 60% increase in fine soil impacts. Such a large 

increase is likely due to poor model performance for fine soil as well as inaccurate projections of 2018 

fine soil emissions, as discussed below. These results cast significant doubt on the projected 2018 total 

light extinction value and resulting visibility degradation. 

In addition, as with any emissions inventory projected into the future, assumptions must be made 

regarding population, and sources (including which sources will be in existence at that time and what the 

activity level of those sources). Based on the concerns with the modeled degradation at the two monitors, 
Page 4 of 5 

ADEQ reviewed the PRP18b emissions inventory and projected light extinction impacts to evaluate its 

accuracy. The following information was found that indicates that the projected degradation will not 

occur: 

Assumption of Growth Factors 

In developing the PRP18b emissions inventory, the WRAP used a variety of growth factors in 

order to use the 2002 emission inventory to project the 201 8 inventory. The WRAP used several 

sources to estimate the growth factors, including DOE for fuel combustion, USDA for 

agricultural sources, CAMD for electric utilities, and EPA's Economic Growth Analysis System 

(EGAS 5.0) for all other sources (except oil and gas). 

EGAS is an economic and activity forecast tool that provides growth factors for developing 

emission inventory projections. EPA recommended the use of EGAS to develop 20 18 projections 

for the WRAP region in 2005. In August of 2006 EPA identified concerns with the EGAS 

model. Specifically, EPA observed a disconnect between the emission forecasts for sources such 

as industrial boilers, petroleum refiners, chemical manufacturing plants, as well as small 

stationary commercial, institutional, and residential non-point sources. According to EPA's 

August 4, 2006 draft document titled Improving EPA Emissions Forecasting For Regulatory 

Impact Analyses, "the discrepancy lead to significant over-prediction of emissions projections.. ." 

While separate methods were used for road dust, agricultural dust, and exotic sources like fire, the 

fugitive dust emissions for Arizona sources such as Portland cement, asphalt batch, materials 

handling, road construction, among many others, were all projected using EGAS which relies on 

population and economic growth predictions to forecast emissions. In addition, the growth 

factors were applied at the state-level, which does not account for the variability in growth within 

various counties and regions in the state. Therefore, the fugitive dust emission in Arizona are 

likely over predicted, thus calling into question the visibility impacts from fine soil across all 

monitors in Arizona, including SAGU I and CHlRI . 

The growth factors used for agricultural tilling were taken from USDA Baseline Projections, 

February 2005. The projections cover a 12-year period from 2003 to 2014 for estimated 

harvested acres of eight major field crops and assume that the 2002 Farm Act remains in effect 

for the entire projection period. The baseline scenario is also based on specific assumptions 

regarding the macroeconomy, policy, weather, and international developments, with no shocks to 

the agricultural market. For the 2002 and 20 18 WRAP modeling scenarios, the projections were 

extrapolated to get estimates for 2002 and 2018. The growth factors were derived from 

estimated data not actual harvested acres for agricultural tilling. Similar to the issues identified 

with the EGAS model, the growth factor derived from the USDA projections does not account 

for changes and variability inherent to agricultural operations. It also does not reflect projections 

based on actual harvested acres. Comparing the 2002-20 18 extrapolated growth rate to the more 

recent USDA projected data shows that the growth factor was should have been 1.2% rather than 

3.6%. Thus statewide emissions from agricultural operations are likely overstated. 

Stationary Source Assumptions 

Assumptions made during the creation of the PRP18b inventory did not include Best Available 

Retrofit Technology (BART) determinations, mostly because such determinations had not been 
Page 5 of5 

made when the inventory was prepared. Instead, the WRAP made assumptions on what limits the 

facilities would be subject to. The following list details changes that should have been 

incorporated into the inventory: 

o Apache Generating Station 

BART limits will reduce the amount of NOx emitted from the facility by 

1,600 tpy as compared to PRP 18b. The Apache Station is the largest source 

near the CHIR I monitor. 

o SRP Coronado 

BART resulted in a 2,000 tpy reduction of SO2 when compared to PRPl8b 

(BART limit 0.08 IbIMMBtu, PRPl8b estimated at 0.15). 

BART resulted in approximately 3,000 tpy reduction of NOx as compared to 

PRP 18b. 

In addition, several other inclusions in the PRPI 8b inventory are likely overstated. The following 

list identifies some of the discrepancies: 

o The Arizona Clean Fuels Refinery (proposed to be built east of Yuma) was included 

in the PRPl8b inventory has not been (and may not be) built. SO2 and NOx 

emissions included in the inventory are 25 1 and 352 tpy, respectively; 

o SO2 projections from the ASARCO Hayden Smelter are 3,000 tons per year higher 

than any time period in the last 10 years. In addition, the company will be required to 

reduce emissions of SO2 as the area is currently exceeding the 1-hour SO2 standard; 

o SO2 projections from the Arizona Portland Cement Plant are 80 tons per year more 

than actually emitted from the facility, even during periods of increased economic 

activity (APC is near the SAGU 1 monitor). 

While the WRAP emissions inventory and modeling is the best information available, and significant 

time and research went into the project, the 0.1 dv and 0.03 dv degradation reported in the SIP submittal 

are well within the uncertainty and error of the model and emissions inventory. Upon further reflection 

ADEQ has concluded that such degradation will likely not occur as there are significant questions about 

the modeling performance and emissions inventory. In addition, the 2005-2009 progress period does not 

reflect the degradation that was predicted. Based on the above discussion, ADEQ asks that EPA approve 

the submitted SIP. If you have any questions, please contact me at (602) 77 1-2288. 

Sincerely, - 

Air ~ualp6Vision 

cc. / Colleen McKaughan, EPA 

Tom Webb, EPA