Prepared for: Prepared by: 

CalPortland Company AECOM 

Glendora, CA Camarillo, CA 

60282724 

March 2014

Environment

Evaluation of EPA’s Reasonable Progress 

Analysis for Kiln 4 at CalPortland 

Company’s Rillito Cement Plant 
Prepared for: Prepared by: 

CalPortland Company AECOM 

Glendora, CA Camarillo, CA 

60282724 

March 2014

Environment

Evaluation of EPA’s Reasonable Progress 

Analysis for Kiln 4 at CalPortland 

Company’s Rillito Cement Plant 

_________________________________ 

Prepared By Steven L. Heisler 

_________________________________ 

Reviewed By Sara J. Head 
AECOM Environment 

Evaluation of EPA’s Reasonable Progress Analysis for CalPortland Rillito Kiln 4 March 2014 

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Contents 

1.0 Introduction ............................................................................................................... 1-1

2.0 Nitrogen Oxides Control Efficiency for Applying Selective Non-Catalytic 

Reduction to Kiln 4.................................................................................................... 2-1

3.0 Costs and Cost Effectiveness for Applying Selective Non-Catalytic 

Reduction to Kiln 4.................................................................................................... 3-1

4.0 Visibility Modeling to Evaluate Visibility Improvements.......................................... 4-1

4.1 Differences between EPA and AECOM Visibility Modeling ............................................4-1

4.1.1 Errors in Emissions from Kilns 1 through 3 at the Rillito Cement Plant .............4-1

4.1.2 Errors in Rillito Kiln 4 Stack Parameters .........................................................4-2

4.1.3 Coarse Particle Geometric Mean Diameter and Minimum Turbulence 

Velocities ......................................................................................................4-3

4.1.4 Monthly Background Ammonia Concentrations ..............................................4-3

4.2 Visibility Modeling Results ...........................................................................................4-5

5.0 Conclusions .............................................................................................................. 5-1
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List of Tables 

Table 4-1 Corrected Hourly Emission Rates for Kilns 1 through 3 for Visibility Modeling.....................4-2

Table 4-2 Corrected Stack Parameters for Kiln 4 for Visibility Modeling .............................................4-2

Table 4-3 Background Monthly Ammonia Concentrations (ppb) Used in the Modeling .......................4-5

Table 4-4 EPA and AECOM Visibility Modeling Results with Monthly Ammonia Background for 

AECOM Modeling ......................................................................................................4-7

Table 4-5 EPA and AECOM Visibility Modeling Results with Constant 1 ppb 

Ammonia Background for AECOM Modeling ..............................................................4-8

List of Figures 

Figure 2-1 Depiction of Rillito Cement Plant Kiln 4 Modified Loop Calciner and Mojave Cement 

Plant Kiln Calciner .....................................................................................................2-4

Figure 4-1 IMPROVE NHx Concentrations from April 2011 to January 2012 .................................4-4

Figure 4-2 2009 IMPROVE Composition Data for Saguaro East National Park .............................4-5
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List of Abbreviations 

oC degrees Celsius 

o

F degrees Fahrenheit 

AZ Arizona 

BART Best Available Retrofit Technology 

CA California 

CDPHE Colorado Department of Public Health and Environment 

CO carbon monoxide 

CO2 carbon dioxide 

CPC CalPortland Company 

dv deciview 

EPA United States Environmental Protection Agency 

FIP Federal Implementation Plan 

FR Federal Register 

H hydrogen 

H2O water 

IMPROVE Interagency Monitoring of Protected Visual Environments 

IWAQM Interagency Workgroup on Air Quality Modeling 

N2 molecular nitrogen 

NH2 amine radical 

NH3 ammonia 

NHx ammonia plus ammonium ion 

NM National Monument 

NO nitric oxide 

NO2 nitrogen dioxide 
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NOx nitrogen oxides 

NP National Park 

O2 molecular oxygen 

OH hydroxyl radical 

PM10 particles smaller than 10 microns diameter 

ppb part per billion 

RP Reasonable Progress 

SIP State Implementation Plan 

SNCR selective non-catalytic reduction 

SO2 sulfur dioxide 

tpy tons per year 

TSD Technical Support Document 

WA Wilderness Area 
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Executive Summary 

On February 18, 2014, the United States Environmental Protection Agency (EPA) published in the Federal 

Register (79 FR 9318) a proposed Federal Implementation Plan (FIP) to address the requirements of the 

Regional Haze Rule and interstate visibility transport for the disapproved portions of Arizona’s Regional 

Haze State Implementation Plan (SIP) as described in EPA’s final rule published on July 30, 2013. As part 

of the proposed FIP, EPA is proposing to require nitrogen oxides (NOx) emissions reductions consistent 

with the application of Selective Non-Catalytic Reduction (SNCR) on Kiln 4 at the CalPortland Company 

(CPC) Rillito Cement Plant. The proposed requirement is based on a Reasonable Progress (RP) analysis 

conducted by EPA for the CPC Rillito Cement Plant. 

Various aspects of EPA’s RP analysis for Kiln 4 at the Rillito Cement Plant have been evaluated by 

AECOM for this report. These aspects include: 

x The NOx control efficiency that is assumed for applying SNCR to Kiln 4; 

x The costs for applying SNCR to Kiln 4; and 

x Modeling conducted to estimate the degree of improvement in visibility that could result from 

applying SNCR to reduce NOx emissions from Kiln 4. 

EPA’s assumption of a 50 percent NOx control efficiency for applying SNCR to Kiln 4 is too high. This 

control efficiency was based in part on an SNCR optimization report for CPC’s Mojave Plant in California 

submitted to EPA on August 30, 2013. Emission data provided in this report indicates a range of SNCR 

control efficiency of 30 percent to 60 percent at the Mojave Plant, depending upon operating parameters. 

Although SNCR control efficiencies as high as 60 percent were observed at the Mojave Plant, there are 

differences between Kiln 4 at the Rillito Cement Plant and the cement kiln at the Mojave Plant which would 

lead to a lower NOx control efficiency from applying SNCR to Kiln 4. Although site-specific tests would be 

required to quantify the control efficiencies that might be achieved with SNCR for Kiln 4, CPC has 

considered these differences between Kiln 4 at Rillito and the cement kiln at the Mojave Plant and, based 

on its engineering judgment, concluded that 35 percent NOx control efficiency would be an appropriate 

estimate for Kiln 4. 

EPA’s estimate of the annualized cost for applying SNCR to Kiln 4 of $1,089,566 is too low. Based on 

more accurate estimates of the annual cost for ammonia reagent, a more reasonable annualized cost 

estimate is $1,348,084. The resulting cost effectiveness, based on a 35 percent NOx control efficiency, is 

$1,850 per ton of NOx removed, which is approximately 78 percent higher than EPA’s estimate of $1,047 

per ton of NOx removed. 

AECOM conducted additional visibility modeling to estimate the potential improvements in visibility that 

would result from applying SNCR with a NOx control efficiency of 35 percent to Kiln 4. In addition to the 

difference in the assumed SNCR NOx control efficiency, AECOM’s visibility modeling included the 

following differences from EPA’s modeling: 

x Errors in emissions from Kilns 1 through 3 at the Rillito Cement Plant were corrected; 

x Errors in the stack parameters for Kiln 4 were corrected; 

x Values used for the coarse particle geometric mean diameter and for minimum turbulence 

velocities differed from those used by EPA; and 
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x Visibility was calculated using both constant and seasonal NH3 background concentrations. 

The highest modeled visibility benefits at a Class I area from applying SNCR to Kiln 4 with an assumed 

NOx control efficiency of 35 percent is 0.15 deciview (dv) with a seasonally varying NH3 background 

concentration and 0.18 dv with a constant 1 part per billion (ppb) NH3 background concentration. These 

visibility improvements are substantially less than the maximum improvement of 0.24 dv indicated by 

EPA’s modeling and too low to be detected by the available technology for particulate monitors (much less 

than 0.3 dv) and less than 18 percent of the perceptible levels that can be visually detected (1 dv). 

Furthermore, in its RP analysis for Springerville Units 1 and 2 for the proposed FIP, EPA concluded that 

“While the cost per ton for SNCR may be reasonable, the projected visibility benefits are relatively small 

(0.18 dv at the most affected area)” and did not propose additional controls on these units. Consistent 

with this conclusion, it would not be reasonable to propose the application of SNCR to Kiln 4 at the Rillito 

Cement Plant based on the similar small benefit. 
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1.0 Introduction 

On February 18, 2014, the United States Environmental Protection Agency (EPA) published in the 

Federal Register (79 FR 9318) a proposed Federal Implementation Plan (FIP) to address the 

requirements of the Regional Haze Rule and interstate visibility transport for the disapproved portions 

of Arizona’s Regional Haze State Implementation Plan (SIP) as described in EPA’s final rule 

published on July 30, 2013. As part of the proposed FIP, EPA is proposing to require nitrogen oxides 

(NOx) emissions reductions consistent with the application of Selective Non-Catalytic Reduction 

(SNCR) on Kiln 4 at the CalPortland Company (CPC) Rillito Cement Plant. The proposed 

requirement is based on a Reasonable Progress (RP) analysis conducted by EPA for the CPC Rillito 

Cement Plant. 

This document presents AECOM’s evaluation of various aspects of EPA’s RP analysis for Kiln 4 at the 

Rillito Cement Plant. These aspects include: 

x The NOx control efficiency that is assumed for applying SNCR to Kiln 4; 

x The costs for applying SNCR to Kiln 4; and 

x Modeling conducted to estimate the degree of improvement in visibility that could result from 

applying SNCR to reduce NOx emissions from Kiln 4. 
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2.0 Nitrogen Oxides Control Efficiency for Applying Selective 

Non-Catalytic Reduction to Kiln 4 

The SNCR process is basically the injection of aqueous or anhydrous ammonia (NH3) or urea into the 

cement kiln flue gas at a suitable temperature. SNCR removes NOx (90 to 95 percent of NOx in flue 

gas is nitric oxide, NO) by a two-step process, as follows: 

x Ammonia reacts with available hydroxyl radicals (OH) to form amine radicals (NH2) and water 

(H2O): 

NH3 + OH ĺ NH2 + H2O (1) 

x Amine radicals combine with NO to form nitrogen (N2) and water: 

NH2 + NO ĺ N2 + H2O (2) 

These 2 steps are typically expressed as follows: 

4 NO + 4 NH3 + O2ĺ 4 N2 + 6 H2O (3) 

and 

4 NH3 + 2 NO2 + O2ĺ 3 N2 + 6 H2O (4) 

Equation 3 is the predominant reaction because 90 to 95 percent of NOx in flue gas is NO. 

These equations suggest that SNCR will function best in an oxidizing atmosphere, whereas the 

following equation shows that in a reducing atmosphere carbon monoxide (CO) competes with 

ammonia for available OH radicals, thus inhibiting reaction 1. 

CO + OH ĺ CO2 + H (5) 

The temperature window for the SNCR reactions is critical. At higher temperatures, ammonia will 

react with oxygen, thereby increasing NOx concentrations. At lower temperatures, the rates of NOx 

reduction reactions become too slow, resulting in excessive ammonia slip (high concentrations of 

unreacted ammonia in exhaust) or the excessive build-up of ammonia in raw materials. The optimum 

range is 870 oC to 1,100 °C (1,600 oF to 2,000 °F). 

In a preheater/precalciner kiln, reagent injection occurs after the exit of the kiln in the calciner or the 

lower part of the preheater tower. This injection location is generally readily accessible using 

conventional injection technology. 

EPA assumed a 50 percent NOx control efficiency for applying SNCR to Kiln 4 in its RP analysis. 

This control efficiency was based in part on an SNCR optimization report for CPC’s Mojave Plant in 

California submitted by CPC to EPA on August 30, 2013. The report provided emission data from the 

first seven months of 2013 in which adjustments were made to multiple control technology operating 
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parameters. Emission data provided in this report indicates a range of SNCR control efficiency of 30 

percent to 60 percent at the Mojave Plant, depending upon operating parameters. However, the 

emission data from the Mojave optimization period are highly variable (due to the operational 

variability that is part of the optimization), and CPC has not determined what control efficiency or 

emission rate is appropriate to use as the basis for an emission limit for the Mojave Plant. 

Although SNCR control efficiencies as high as 60 percent were observed at the Mojave Plant, there 

are differences between Kiln 4 at the Rillito Cement Plant and the cement kiln at the Mojave Plant. 

The designs of the two kilns are not the same; Kiln 4 at Rillito is older than the kiln at the Mojave 

Plant, and it has a modified loop calciner, which is different from the precalciner on the kiln at the 

Mojave Plant. The precalciner on the cement kiln at the Mojave Plant and the modified loop calciner 

on Kiln 4 are illustrated in Figure 2-1. 

The following differences between Kiln 4 at Rillito and the cement kiln at the Mojave Plant would lead 

to a lower NOx control efficiency for SNCR for Kiln 4: 

x Temperatures in the reasonably accessible potential NH3 injection locations for Kiln 4 are only 

1,100 oF to 1,500 oF, which are below the lower limit of the optimum temperature range of 

1,600 oF to 1,900 oF, while temperatures at the NH3 injection locations for the kiln at the 

Mojave Plant are in the range of 1,650 oF to 1,750 oF, which are within the optimum 

temperature range. Therefore, the rates of NOx reduction reactions would be much slower 

for Kiln 4, leading to less reduction of NOx emissions. 

x Because of the differences in the type of calciner, O2 concentrations in the Kiln 4 exhaust are 

substantially lower than O2 concentrations in the exhaust from the cement kiln at the Mojave 

Plant, which would lead to a lower rate for Reaction 3 above and, as a result, a lower control 

efficiency. 

x As depicted in Figure 2-1, the precalciner on the cement kiln at the Mojave Plant is a cyclonic 

vessel where fuel and tertiary air are injected in such a way as to promote efficient 

combustion within the small vessel. The cyclonic flow created in the vessel provides good 

mixing between the injected NH3 and the kiln exhaust gas, which promotes contact between 

the NH3 and the other reactants in the gases. In contrast, the modified loop calciner on Kiln 4 

at the Rillito Cement Plant depicted in Figure 2-1 is essentially a duct without a vessel. 

Because of the duct design there is poor mixing of the fuel and air providing little opportunity 

for the NH3 and exhaust gases to interact. The inferior mixing of the Kiln 4 modified loop 

calciner impedes the ability of the SNCR reactions to reduce the NOx concentrations. 

x CO emissions from Kiln 4 are approximately 10 times higher than CO emissions from the 

cement kiln at the Mojave Plant. As shown in Equation 5 above, the much higher CO 

concentrations in the Kiln 4 exhaust would compete with NH3 for hydroxyl radicals, which 

would reduce the NOx control effectiveness. 

x Although the retention time in the modified loop calciner on Kiln 4 is slightly longer than the 

retention time in the precalciner on the kiln at the Mojave Cement Plant (approximated 1.5 

seconds for Kiln 4 and 0.5 to 0.75 seconds for the Mojave kiln), the longer retention time does 

not offset the substantially lower reaction rates caused by the lower calciner temperatures, 

lower O2 concentrations, poorer mixing and higher CO concentrations. 

Because of these differences, the SNCR NOx control efficiencies obtained for the cement kiln at the 

Mojave Plant cannot be applied to Kiln 4 at Rillito. Although site-specific tests would be required to 

quantify the control efficiencies that might be achieved with SNCR for Kiln 4, CPC has considered 
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these differences between Kiln 4 at Rillito and the cement kiln at the Mojave Plant and, based on its 

engineering judgment, concluded that 35 percent NOx control efficiency would be an appropriate 

estimate for Kiln 4. 

EPA also cited NOx control efficiencies between 45 percent and 50 percent for four additional 

preheater/precalciner cement kilns in the TSD to support the assumption of 50 percent NOx control 

efficiency for applying SNCR to Kiln 4. EPA did not provide any design or operating details for these 

four kilns to allow a comparison with Kiln 4. However, it is unlikely that these kilns have modified loop 

calciners so differences between these kilns and Kiln 4 may be similar to the differences between the 

Mojave calciner and the Kiln 4 calciner in Rillito. Therefore, it is not appropriate to apply the SNCR 

NOx control efficiencies for these cement kilns to Kiln 4. 
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Figure 2-1 Depiction of Rillito Cement Plant Kiln 4 Modified Loop Calciner and Mojave Cement Plant Kiln Calciner 
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3.0 Costs and Cost Effectiveness for Applying Selective 

Non-Catalytic Reduction to Kiln 4 

For its RP analysis, EPA estimated that the annualized cost for applying SNCR to Kiln 4 would be 

$1,089,566. Based on annual average uncontrolled NOx emissions from Kiln 4 of 2,082 tons per year 

(tpy) and an SNCR control efficiency of 50 percent, EPA estimated that annual average NOx 

emissions would be reduced by 1,041 tpy, resulting in a cost effectiveness of $1,047 per ton of NOx 

reduced. 

EPA’s analysis of the costs for applying SNCR to Kiln 4 is essentially the same as an analysis in 

“Reasonable Progress Analysis for CalPortland Company Rillito Cement Plant Kilns” submitted by 

CPC to EPA on May 9, 2013, except for the estimated annual cost for NH3 reagent for the SNCR 

system. EPA used an NH3 cost of $1,000 per ton, estimated at approximately double historical urea 

price highs (excluding 2008 high), while CPC used an estimated NH3 cost of $1,640 per ton. 

CPC has refined its estimate of NH3 costs based on information provided by CPC’s aqueous NH3

vendor, Airgas Specialty Products, and projections to 2018, which is the earliest that SNCR would 

begin operating on Kiln 4. The estimated price is $0.1204 per pound for 19 percent aqueous NH3, 

plus $1.31 per mile fuel surcharge from Buckeye, AZ to Rillito per 15-ton tanker truck load, plus a 

$25.00 hazardous material manifest fee per truck load. The travel distance from Buckeye to Rillito 

from Google Maps is approximately 131 miles, leading to an estimated cost for a 15-ton tanker truck 

load of: 

15 tons x 2,000 pounds/ton x $0.1204/pound + 131 miles x $1.31/mile + $25.00 = 

$3,809 per 15 tons 

The estimated cost per ton of ammonia would be: 

$3,809 / 15 tons solutions / 0.19 tons NH3/ton solution = $1,336 per ton NH3

EPA calculated the annual NH3 usage by assuming the use of one mole of ammonia for each mole of 

uncontrolled NOx. The resulting annual ammonia usage, based on 2,082 tpy uncontrolled NOx, is: 

2,082 tpy NOx / 46 pounds NOx per pound-mole x 17 pounds NH3 per pound-mole = 

769.4 tons NH3 per year 

EPA’s estimate of annual costs for NH3 is 769.4 tpy x $1,000 per ton NH3 = $769,400 

Annual NH3 costs using CPC’s revised NH3 price is 769.4 tpy x $1,336 per ton NH3 = $1,027,918 

Thus, the estimated annual NH3 cost based on CPC’s estimated NH3 price is $258,518 more than 

EPA’s estimate, and the estimated total annualized cost for SNCR is $1,089,566 + $258,518 = 

$1,348,084. As discussed in Section 2.0, CPC estimates that 35 percent is an appropriate NOx 

control efficiency for applying SNCR to Kiln 4. The resulting annual reduction in NOx emissions would 

be 0.35 x 2,082 tpy uncontrolled NOx = 728.7 tpy, resulting in a cost effectiveness of $1,850 per ton of 

NOx reduced, which is approximately 78 percent higher than EPA’s estimate. 
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4.0 Visibility Modeling to Evaluate Visibility Improvements 

EPA and its contractor, the University of North Carolina, conducted visibility modeling to estimate the 

potential improvement in visibility at Class I areas that could result from applying SNCR with a NOx 

control efficiency of 50 percent to Kiln 4 at Rillito. EPA concluded that applying SNCR to Kiln 4 with a 

NOx control efficiency of 50 percent could improve visibility by 0.24 deciviews (dv) at the eastern unit 

of Saguaro National Park (NP), by 0.19 dv at Galiuro Wilderness Area (WA), and by less for other 

areas. 

As discussed in Section 2, CPC has concluded that assuming a NOx control efficiency of 35 percent 

for Kiln 4 is more appropriate than assuming a control efficiency of 50 percent. Therefore, AECOM 

has conducted additional visibility modeling to estimate the potential improvements in visibility that 

would result from applying SNCR with a NOx control efficiency of 35 percent to Kiln 4. 

In addition to the difference in the assumed SNCR NOx control efficiency, AECOM’s visibility 

modeling included the following differences from EPA’s modeling: 

x Errors in emissions from Kilns 1 through 3 at the Rillito Cement Plant were corrected; 

x Errors in the stack parameters for Kiln 4 were corrected; 

x Values used for the coarse particle geometric mean diameter and for minimum turbulence 

velocities differed from those used by EPA; and 

x Visibility was calculated using both constant and monthly NH3 background concentrations. 

These differences are described in Section 4.1. The rest of the modeling procedures were the same 

as used by EPA and its contractor, including the base case NOx emission rate for Kiln 4. Visibility 

modeling results are presented in Section 4.2. 

4.1 Differences between EPA and AECOM Visibility Modeling 

4.1.1 Errors in Emissions from Kilns 1 through 3 at the Rillito Cement Plant 

Emissions from Kilns 1 through 3 at the Rillito Plant used by EPA and its contractor for the modeling 

are calculated in the Excel file: 

E-13_2014-01_Cement_Plant_Emission_Calculations_(final_for_NPRM_docket).xlsx 

This Excel file can be found in the docket for the proposed FIP. The following errors were identified in 

this file: 

x The hourly maximum feed rates for Kilns 1 through 3 were not converted to clinker production 

rates in the cell labeled as tons/hr under clinker production rate. Additionally, the value 

entered was 17 tons/hour, but the actual capacity is 19 tons/hour. 

x Total clinker production for Kilns 1 through 3 for 2006 should be 368,314 tpy instead of 

368,315 tpy. 
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x Total clinker production for Kilns 1 through 3 for 2005 should be 342,999 tpy instead of 

343,000 tpy. 

x The hourly NOx and sulfur dioxide (SO2) emission rates for Kilns 1 through 3 in the worksheet 

labeled “CalPortland Cement – Model” are not the values in the worksheet labeled 

“CalPortland – Base Case.” 

x The hourly PM10 emission rate for Kilns 1 through 3 in in the worksheet labeled “CalPortland 

Cement – Model” is three times the value calculated for all three kilns combined in the 

worksheet labeled “CalPortland – Base Case.” 

Hourly NOx, SO2 and PM10 emission rates listed for the modeling in the Excel file and the corrected 

values are shown in Table 4-1. 

Table 4-1 Corrected Hourly Emission Rates for Kilns 1 through 3 for Visibility 

Modeling 

Pollutant EPA Emission Rate 

(pounds/hour) 

Corrected Emission Rate 

(pounds/hour) 

NOx 450 403 

SO2 10.64 8.47 

PM10 30.02 10.01 

4.1.2 Errors in Rillito Kiln 4 Stack Parameters 

Stack parameters for the cement kilns at the Rillito Plant used by EPA and its contractor for the 

modeling are calculated in the Excel file: 

E-13_2014-01_Cement_Plant_Emission_Calculations_(final_for_NPRM_docket).xlsx 

This Excel file can also be found in the docket for the proposed FIP. The stack parameters in the 

worksheet labeled “Stack Parameters” are the parameters for a cement kiln that was proposed for 

construction at the Rillito Cement Plant to replace Kilns 1 through 4 (Kiln 6). However, this kiln has 

not been constructed. The stack parameters in the Excel file and the correct stack parameters for Kiln 

4 are listed in Table 4-2. It should also be noted that the visibility modeling for “Reasonable Progress 

Analysis for CalPortland Company Rillito Cement Plant Kilns” submitted by CPC to EPA on May 9, 

2013 also used the incorrect stack parameters for Kiln 4. 

Table 4-2 Corrected Stack Parameters for Kiln 4 for Visibility Modeling 

Parameter EPA Value Correct Kiln 4 Value 

Height (meters) 40 22.86 

Diameter (meters) 4.88 3.048 

Exit Velocity (meters/second) 14.58 16.22 

Exit Temperature (degrees Kelvin) 478 519 
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4.1.3 Coarse Particle Geometric Mean Diameter and Minimum Turbulence Velocities 

EPA’s contractor assumed a geometric mean diameter for coarse particulate matter of 0.48 microns in 

its CALPUFF modeling. Because coarse particles are particles larger than 2.5 microns diameter, 

AECOM assumed a geometric mean diameter of 6 microns. 

EPA’s subcontractor used non-default minimum turbulence velocities sigma-v (SVMIN) and sigma-w 

(SWMIN) for each stability class over land and over water of 0.5 m/s. According to comments in their 

CALPUFF modeling files, using the default values gave them an error message and the only way to 

bypass it and run the model to completion was to set SVMIN and SWMIN to 0.5. AECOM used the 

default values without encountering errors from CALPUFF. 

4.1.4 Monthly Background Ammonia Concentrations 

EPA’s subcontractor used a constant 1 part per billion (ppb) ammonia background concentration in 

the POSTUTIL post-processor to calculate the partitioning of nitrate between gaseous nitric acid and 

particulate ammonium nitrate. The Technical Support Document (TSD) for the proposed rule states 

that “Ambient ammonia measurements for use as input to modeling are scarce, and measurements 

that include it in the form of ammonium even scarcer. In the absence of compelling ammonia 

background estimates, the EPA IWAQM Phase 2 guidance recommends the use of a 1 ppb ammonia 

background for arid lands, which includes Arizona.” 

At the time the IWAQM Phase 2 guidance was developed, CALPUFF did not have the capability of 

accommodating monthly varying background ammonia. However, the current version does have this 

capability. Additionally, the IMPROVE monitoring network recently began to incorporate routine 

measurements of gaseous ammonia at specific sites. A recently issued technical paper1 on this 

subject showed monthly NHx (NHx = ammonia plus ammonium ion) measurements at these sites, 

including one in southern Arizona (Chiricahua), less than 200 kilometers (124 miles) from the Rillito 

Cement Plant. A review of the measurements taken to date at these sites (see Figure 4-1) indicates 

that ammonia concentrations less than 1 ppb (e.g., 0.5 ppb) are present at this site in winter. 

In an independent analysis, the Colorado Department of Public Health and Environment (CDPHE) 

performed a sensitivity modeling analysis to explore the effect of the ammonia concentration input to 

CALPUFF on the predicted visibility impacts for a source with high NOX emissions relative to SO2

emissions.2 It is noteworthy that the largest sensitivity occurs for ammonia input values between 1 

and 0.1 ppb. In that range, the difference in the peak visibility impacts predicted by CALPUFF is 

slightly more than a factor of 3 between ammonia concentration input values of 1 and 0.1 ppb. This 

sensitivity analysis shows that the choice of background ammonia is very important in terms of the 

magnitude of visibility impacts predicted by CALPUFF. Furthermore, since the results are highly 

 

1

 Chen, X., D. Day, B. Schichtel, W. Malm, J. Mojica, C. McDade, E. Hardison, S. Kreidenweis, and J. Collett, 

2012. A Pilot Monitoring Study of Atmospheric NHx at Selected IMPROVE Sites. Extended Abstract # 19. 

Presented at the 2012 Aerosol and Atmospheric Optics: Visibility & Air Pollution Specialty Conference, held 

September 25-28th, 2012 in Whitefish, MT. Air & Waste Management Association, Pittsburgh, PA. 

2

 Supplemental BART Analysis: CALPUFF Protocol for Class I Federal Area Visibility Improvement Modeling 

Analysis (DRAFT), revised June 25, 2010, available at http://www.colorado.gov/airquality/documents/DraftColoradoSupplementalBARTAnalysisCALPUFFProtocol-25June2010.pdf. 
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sensitive to the NH3 value, the assumption of 1 ppb for winter likely introduces over-predictive 

conservatism in the modeling results for NOx effects upon haze. 

The visibility composition plots depicted in Figure 4-2 from an IMPROVE monitor located in Saguaro 

East National Park show that the majority of nitrate (shown by the red portions of the composition 

columns) forms during cold temperature (in the modeled predictions and in the real world) and, 

therefore, the model is not sensitive to the selected ammonia values in summer, but would be highly 

sensitive to values in winter months. 

Based upon this available ammonia measurement information (which conservatively includes both 

gaseous and particulate form concentration contributions), AECOM has developed a set of monthlyvarying ammonia background concentrations (see Table 4-3) that correspond to the actual measured 

values noted above. Consistent with the EPA values, an ammonia background of 1 ppb is used for 

many of the non-winter months.

Figure 4-1 IMPROVE NHx Concentrations from April 2011 to January 2012 
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Figure 4-2 2009 IMPROVE Composition Data for Saguaro East National Park 

Table 4-3 Background Monthly Ammonia Concentrations (ppb) Used in the Modeling 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

0.5 0.5 0.6 0.7 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.8 

The use of monthly background NH3 concentrations is consistent with visibility modeling conducted by 

EPA for Best Available Retrofit (BART) sources in western Wyoming (79 FR 5111-5113). For that 

modeling, EPA used monitored NHx from a site in western Wyoming that was within the modeling 

domain for the sources in western Wyoming to estimate monthly background NH3 concentrations for 

the visibility modeling. As stated by EPA, “ the IWAQM Phase 2 report recommends use of the 

background values it provides for different land use categories, unless specific data is available in the 

modeling domain as a more accurate substitute for its recommended default values, and allows for 

the consideration of background ammonia concentrations that vary seasonally or spatially.” Thus, the 

use of monitored NHx concentrations from Chiricahua to estimate monthly background NH3

concentrations for visibility modeling for the Rillito Cement Plant is similar to EPA’s use of monitored 

NHx concentrations to estimate monthly background NH3 concentrations for visibility modeling for the 

western Wyoming sources. 

4.2 Visibility Modeling Results 

Results from the visibility modeling for Class I areas within 300 kilometers (km) of the CPC Rillito 

Cement Plant are presented in Tables 4-4 and 4-5. These tables list the visibility impacts for the base 

case and the visibility impacts and benefits relative to the base case for the application of SNCR to 

Kiln 4. Results from both EPA’s and AECOM’s modeling are listed. The CALPOST post-processor 

method 8b (new IMPROVE extinction calculation equation and impacts relative to 20 percent best 

natural condition days) was used to obtain both the EPA and AECOM results. Table 4-4 shows 

results using seasonally varying NH3 background concentrations for the AECOM modeling and Table 

4-5 shows results using a constant 1 ppb NH3 background concentration for the AECOM modeling. 
AECOM Environment 

Evaluation of EPA’s Reasonable Progress Analysis for CalPortland Rillito Kiln 4 March 2014 

4-6

As shown in Table 4-4, AECOM’s modeling with a seasonally varying NH3 background concentration 

indicates that applying SNCR to Kiln 4 with a NOx control efficiency of 35 percent could improve 

visibility by 0.15 dv at Galiuro WA, by 0.14 dv at the eastern unit of Saguaro NP, and by less for other 

areas. Also, as shown in Table 4-5, AECOM’s modeling with a constant 1 ppb NH3 background 

concentration indicates that applying SNCR to Kiln 4 with a NOx control efficiency of 35 percent could 

improve visibility by 0.18 dv at the eastern unit of Saguaro NP and by 0.16 dv at Galiuro WA. These 

visibility improvements are substantially less than the maximum improvement of 0.24 dv at the eastern 

unit of Saguaro NP indicated by EPA’s modeling. 
AECOM Environment 

Evaluation of EPA’s Reasonable Progress Analysis for CalPortland Rillito Kiln 4 March 2014 

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Table 4-4 EPA and AECOM Visibility Modeling Results with Monthly Ammonia 

Background for AECOM Modeling 

Class I Areaa Visibility Impacts 

(dv) 

Visibility Benefits 

(dv) 

Base Case SNCR on Kiln 4 SNCR on Kiln 4 

EPA AECOM EPA AECOM EPA AECOM 

Chiricahua NM 0.25 0.21 0.19 0.17 0.06 0.04 

Chiricahua WA 0.23 0.19 0.18 0.15 0.05 0.03 

Galiuro WA 1.02 0.88 0.83 0.72 0.19 0.15 

Gila WA 0.12 0.10 0.09 0.08 0.03 0.02 

Mazatzal WA 0.13 0.10 0.10 0.08 0.03 0.02 

Mount Baldy WA 0.11 0.09 0.08 0.07 0.03 0.02 

Petrified Forest NP 0.11 0.09 0.08 0.07 0.03 0.02 

Pine Mountain WA 0.11 0.08 0.09 0.07 0.02 0.02 

Saguaro NP 1.26 0.97 1.02 0.83 0.24 0.14 

Sierra Ancha WA 0.13 0.10 0.10 0.08 0.03 0.02 

Superstition WA 0.30 0.23 0.24 0.19 0.06 0.04 

Sycamore Canyon WA 0.09 0.07 0.07 0.06 0.02 0.01 

Maximum 1.26 0.97 1.02 0.83 0.24 0.15 

Cumulative (sum) 3.85 3.10 3.07 2.58 0.78 0.52 

Number of areas >= 0.5 dv 2 2 2 2 0 0 

a

 NM = National Monument, NP = National Park, WA = Wilderness Area 
AECOM Environment 

Evaluation of EPA’s Reasonable Progress Analysis for CalPortland Rillito Kiln 4 March 2014 

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Table 4-5 EPA and AECOM Visibility Modeling Results with Constant 1 ppb Ammonia 

Background for AECOM Modeling 

Class I Areaa Visibility Impacts 

(dv) 

Visibility Benefits 

(dv) 

Base Case SNCR on Kiln 4 SNCR on Kiln 4 

EPA AECOM EPA AECOM EPA AECOM 

Chiricahua NM 0.25 0.23 0.19 0.19 0.06 0.04 

Chiricahua WA 0.23 0.20 0.18 0.17 0.05 0.04 

Galiuro WA 1.02 0.93 0.83 0.77 0.19 0.16 

Gila WA 0.12 0.10 0.09 0.08 0.03 0.02 

Mazatzal WA 0.13 0.11 0.10 0.09 0.03 0.02 

Mount Baldy WA 0.11 0.09 0.08 0.08 0.03 0.02 

Petrified Forest NP 0.11 0.10 0.08 0.08 0.03 0.02 

Pine Mountain WA 0.11 0.09 0.09 0.07 0.02 0.02 

Saguaro NP 1.26 1.08 1.02 0.90 0.24 0.18 

Sierra Ancha WA 0.13 0.11 0.10 0.09 0.03 0.02 

Superstition WA 0.30 0.27 0.24 0.23 0.06 0.05 

Sycamore Canyon WA 0.09 0.08 0.07 0.06 0.02 0.02 

Maximum 1.26 1.08 1.02 0.90 0.24 0.18 

Cumulative (sum) 3.85 3.39 3.07 2.80 0.78 0.59 

Number of areas >= 0.5 dv 2 2 2 2 0 0 

a

 NM = National Monument, NP = National Park, WA = Wilderness Area 
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Evaluation of EPA’s Reasonable Progress Analysis for CalPortland Rillito Kiln 4 March 2014 

5-1

5.0 Conclusions 

The evaluations and analyses presented in this document lead to the following conclusions regarding 

EPA’s RP analysis for Kiln 4 at CPC’s Rillito Cement Plant: 

x EPA’s assumption of a 50 percent NOx control efficiency for applying SNCR to Kiln 4 is too 

high. Based on differences between Kiln 4 at the Rillito Cement Plant and the cement kiln at 

CPC’s Mojave Plant in California, a control efficiency of 35 percent for applying SNCR to Kiln 

4 is considered to be more appropriate. 

x EPA’s estimate of the annualized cost for applying SNCR to Kiln 4 of $1,089,566 is too low. 

Based on more accurate estimates of the annual cost for ammonia reagent, a more 

reasonable annualized cost estimate is $1,348,084. The resulting cost effectiveness, based 

on a 35 percent NOx control efficiency, is $1,850 per ton of NOx removed, which is 

approximately 78 percent higher than EPA’s estimate of $1,041 per ton of NOx removed. 

x The highest modeled visibility benefits at a Class I area from applying SNCR to Kiln 4 with an 

assumed NOx control efficiency of 35 percent (along with other corrections to the model 

inputs) is 0.15 dv with a monthly varying NH3 background concentration and 0.18 dv with a 

constant 1 ppb NH3 background concentration. These visibility improvements are 

substantially less than the maximum improvement of 0.24 dv indicated by EPA’s modeling 

and too low to be detected by the available technology for particulate monitors (much less 

than 0.3 dv) and less than 18 percent of the perceptible levels that can be visually detected (1 

dv). 

Furthermore, in its RP analysis for Springerville Units 1 and 2 in the proposed FIP, EPA 

concluded that “While the cost per ton for SNCR may be reasonable, the projected visibility 

benefits are relatively small (0.18 dv at the most affected area)” and did not propose 

additional controls on these units. Consistent with this conclusion, it would not be reasonable 

to propose the application of SNCR to Kiln 4 at the Rillito Cement Plant based on the similar 

small benefit.