June 2009 www.aecom.com Page 1 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station 

# Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station

June 18, 2009

Robert Paine, AECOM Environment 1 

### Ivar Tombach, Consultant 2

1 AECOM (d/b/a AECOM Environment), 2 Techno logy Park Drive, Westford, MA. 01886

2 753 Grada Avenue, Camariilo, CA 93010



## INTRODUCTION AND RATIONALE

Ammonia gas in the ambient atmosphere near Navajo Generating Station (NGS) and surrounding Class I areas plays an important role in the formation of visibi lity-impairing ammoniated sulfate and ammonium nitrate particles from SO 2 and NOx emissions from NGS. The amount of available ammonia (NH 3 ) governs the acidity of the sulfate aerosol and the availability of remaining NH 3 can govern the amount of ammonium nitrate (NH 4 HNO 3 ) that can be produced from the NOx. For these r easons, it is important to know the free ammonia concentration (i.e., the concentration of gaseous ammonia in the ambient atmosphere) that could interact with

the NGS emissions.

The geographic area of interest is shown in Figure 1. NGS is in the middle of the map, surrounded by 11 Class 1 areas that lie wholly or parti ally within 300 km of the plant.

To the best of our knowledge, only a few measurem ents of concentrations of ambient ammonia have been made within 200 km of NGS. There were daily measur ements provided by Dr. Jeff Collett for May 2003 in the Grand Canyon, which averaged about 0.56 ppb; these were pr ovided to the FLMs in support of the values used in the Desert Rock PSD permitting. Limited measur ements have been made by the U.S. EPA in the Four Corners area of New Mexico and Colorado, including at Mesa Verde National Park, some 260 km from NGS (Sather et al., 2008). Three-week integrated samples were taken for a year (December 2006 to December 2007) with Ogawa passive samplers. Those samples showed the annual mean ammonia concentration at Mesa Verde NP, the most rural sampling location, to be 0.2 ppb, with a standard deviation of 0.2 ppb. During the coldest months (December-February), 3-week average concentrations never exceeded 0.2 ppb.

Most of the area shown in Figure 1, especially along th e paths from NGS to the clos est Class I areas, is even more arid and less populated than the vicinity of Mesa Ve rde NP. Therefore, it is reasonable to expect that the
ammonia concentrations in the area around NGS will be similar to those measured at Mesa Verde, or perhaps even less. This expectation cannot be veri fied without measurements, however.

The background ammonia concentration is a critical input to the EPA CALPUFF model, which is used to predict visibility impacts from NGS. In the Best Av ailable Retrofit Technology (BART) analysis for NGS, EPA is proposing to utilize significantly higher ammonia background concentrations as input into the CALPUFF model than the values proposed by SRP, which ar e the same as those used in the Desert Rock PSD permitting. Since the background ammonia has a signific ant influence on the magnitude of visibility modelingAECOM Environment

June 2009 www.aecom.com Page 2 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station results, which could affect the outcome of the pendi ng EPA BART determination, SRP requested a proposal

from AECOM to measure ambient ammonia concentrations.

This memo presents a conceptual plan for such monitoring.



## SOURCES OF AMMONIA

Figure 2 shows sources of ammonia emissions that lie wi thin the area of Figure 1 or near it. The emissions shown in Figure 2 were obtained from the US EPA’s AirData web site for 2002. Although ammonia emissions from NGS are listed on the AirData web site, there are no ammonia sources at NGS. Therefore, the value in

EPA’s database for ammonia emissions has been adjusted accordingly. It is evident that there are no quantified ammonia sources along transport routes from NGS to the nearby Class I areas, which implies ammonia concentrations are likely to be ve ry low and quite uniform in that area.



## SCOPE OF MONITORING PROGRAM

Measurements at a representative regional site should give a good picture of the ambient ammonia concentrations that influence the impacts of NGS on haze in the closest and, potentially, the most impacted Class I areas, within 100 km of NGS.

The specific locations of the regional monitoring site will be selected c onsidering the following scientific and logistical factors:

(1) In most circumstances, the ammonia concent ration at the Class I area will determine the nitrate concentration (and, hence, the haz e) affecting the Class I area. However,

there are situations where the chemical reactions are slow enough that the ammonia concentration somewhat upwind of the Cla ss I area will be more representative (and the Park Service seems to desire a location that is not at the receptor end of the trajectory). Since we do not expect mu ch spatial variation in the ammonia concentrations, the exact location of the site is not critical as long as it is not near any

local ammonia source.

(2) The site(s) will need to have electric power, have adequate security, and be reasonably accessible for servicing in all weather conditions during the study period. In this desolate study area, one location that meets these criteria is the IMPROVE monitoring site at each Class I area, but other suitable locations may also be found.

Measurements will be taken during the winter months . During other months of the year, the warm temperatures result in very little nitrate production no matter what the ammonia levels. Although ammonia concentrations are highest during the summer, the lower c oncentrations in the cold and cool months are of

interest here because the lack of available ammonia can li mit the formation of nitrat es during those critical

months.

Samples will be collected with coated annul ar diffusion denuders that are analyzed for NH 3 and related gases and particles at Colorado State Univer sity (CSU). Experience with this measurement method in Wyoming (see Attachment A) suggests that sample durations will have to be about th ree days long in order to quantify concentrations below the 0.2 ppb that is likely to occur during winter.

The study will be managed by AECOM Envi ronment with the consulting assistanc e of Dr. Ivar Tombach. Field sampling will be carried out by Air Resource Specia lists (ARS), and/or SRP personnel. Laboratory analyses will be performed under the direction of Dr. Jeff Collet t at the CSU Atmospheric Science Department, and ARS will process and report the data. (ARS and CSU performed the same roles in the ammonia monitoring inAECOM Environment

June 2009 www.aecom.com Page 3 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station Wyoming that is described in Attachment A.) AECOM and Dr. Tombach will analyze and interpret the results that are provided to reviewing agencies by SRP.



## SUMMARY OF PROJECT STEPS

1. Review Monitoring Program Concepts with EPA and the Federal Land Managers (FLMs)

Items to be addressed in a conference call or meeting include the following:

• Location of the monitoring site

• instrumentation and detection limits

• frequency and duration of sampling

• laboratory procedures

• quality assurance

• reporting of concentrations below the lower quantifiable limit (LQL)

2. Select Actual Monitoring Site

Because of their familiarity with the area, SRP and FLM personnel may be able to offer suggestions for a

location for the site that meets the criteria mentioned earlier. Final site sele ction will be carried out by representatives of SRP, AECOM, and ARS during a 3-day survey field trip. Photographic and mapping documentation for the preferred site will be pr ovided to the reviewing agencies, as noted below.

3. Develop Monitoring Protocol and QAPP

ARS, with contributions from AECOM and SRP, will produce two documents:

(1) A Monitoring Protocol that describes t he elements of the monitoring program in detail, with a description of the site and photographs.

(2) A Quality Assurance Project Plan (QAP P) that is compliant with EPA guidance.

These documents will be provided to EPA and FLMs for their comments.

4. Prepare Site, Install Equipment, and Train Site Operators

ARS will prepare the selected site for monitoring, wi th support from SRP for elec tric power connections, and will install the equipment, verify instrument performance, and calibrate the instruments. Day-to-day operation of the monitoring site will be perform ed by either ARS or SRP personnel.

5. Review Early Monitoring Results

The initial ammonia measurements will be reviewed by AECOM and Dr. Tombach to determine whether the measurements will provide the requi red information. The adequacy of the LQL for 3-day samples will be reviewed and causes for any abnormally hi gh concentrations will be identified if possible. If adjustments to the monitoring program are needed, they will be made at this time and EPA and the FM s will be advised of any changes.AECOM Environment

June 2009 www.aecom.com Page 4 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station 6. Report Monitoring Program Results

ARS will provide a report wi th validated monitoring data and documentation of reasons for data flags. Based on analysis of this data, AECOM will recommend am monia concentration values to use for CALPUFF modeling of NGS emissions.

More details on the monitoring program are provided in Attachment B, in excerpts of an ARS document.



## SCHEDULE

For formal monitoring to begin later this year, the t able below identifies tentat ive dates of key milestones.

Before 15 July 2009 Discuss the conceptual plan with EPA and the FLMs

15 July Begin site selection

15 August Finalize arrangements for selected site

15 September Begin initial monitoring to verify proper operation of the sample
collection, analysis, and data processing system.

Winter 2009 Begin formal monitoring.

sometime after winter 2010 End monitoring.AECOM Environment

June 2009 www.aecom.com Page 5 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station Figure 1: Class I Areas in the Vicinity of the Navajo Generating Station (NGS)AECOM Environment

June 2009 www.aecom.com Page 6 of 6 Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station Figure 2: Ammonia Sources in the Vicinity of the Navajo Generating Station (NGS)

# Attachment A

Air Resource Specialists Inc. Ammonia Monitoring Program

in Wyoming

# NH 3 

# Monitoring in the Upper Green River Basin, Wyoming

Extended Abstract #70

John V. Molenar 1



### H. James Sewell 2


### Jeffrey Collett 3



### Cassie Archuleta 1


### Mark Tigges 1



### Florian M. Schwandner 3


### Suresh Raja 3

1 

### Air Resource Specialists, Inc., 1901 Sharp Po int Drive, Suite E, Fort Collins, CO

80525

2 

### Shell Exploration & Production Company, 4582 S. Ulster Street Parkway, Suite 500, Denver, CO 80237

3 

### Department of Atmospheric Science, Co lorado State University, Fort Collins,

CO 80523-1371

Principal Contact: John V. Molenar, Vice Presiden t, Air Resource Specialists, Inc., 1901 Sharp Point Drive, Suite E, Ft. Collins, CO 80525, phone: 970-484-7941, Fax: 970- 484-3423, email: jmolenar@air-resource.com



## INTRODUCTION
A long term ammonia air monitoring study was initiated in December, 2006 at Boulder, Wyoming, by Shell Exploration & Production Company. The monitoring site is located in the Upper Green River Basin of west ern Wyoming southwest of the Bridger Wilderness, a Class I area with an IM PROVE monitoring site. This region is experiencing rapid development of natural ga s resources with possi ble consequences of air quality and visibili ty impacts in the Bridger Wilderness. Only very limited short-term

ammonia measurements were previously available for th is region. Thus, the primary objective of this study is to characteri ze the local airborne nitrogen budget and, specifically, ammonia concentrations and concen trations of related ga ses and particles in the basin for at least one year. Gaseous and particulate samples were collected twice per week (integrated 3-day and 4-day samp les) beginning December 15, 2006 and will continue through May, 2008. Samples were coll ected using coated annular denuders and stacked filters in a University Research Gl assworks (URG) sampler. The Colorado State University Atmospheric Science Department provided laboratory-pre pared sample media and laboratory analysis for gas and part icle concentrations. Standard operating procedures, technical instruc tions, and a QAPP for instrume nt installation, operation and maintenance, field sampling, filter handling, a nd laboratory analyses were developed and submitted to Wyoming Department of Envir onmental Quality – Air Quality Division.

## MONITORING AND LABO RATORY PROCEDURES
Table 1 lists the instrumentation used and pa rameters monitored for the Boulder station ammonia study. Scheduled denuder and filter ch anges were performed twice per week, providing three- to four-day integrated sa mples for the duration of the study period.

Ammonia concentrations and the concentratio ns of related gases and particles were measured using coated annular denuders and stacked filters in a University Research Glassworks (URG) sampler. The Colorado State University Atmospheric Science Department provided laboratory-prepared samp le media and laboratory analysis for gas and particle concentrations. The two-channe l sampler operated con tinuously, the air flow being controlled by a programmable pump w ith a mass flow sensor, and subsequent volumetric gas flow meters. The sampling me thod requires that metered air is drawn through a PM 2.5 

### size selective cyclone inlet, then th rough a series of annular denuders and

filters. The denuders are coated with an acid- based substrate to collect ammonia gas. A second denuder is coated with NaCl to collect gaseous nitric acid. A subsequent stack of two filters is utilized to collect particles. A nylon filter collects pa rticles, and a second, acid-coated filter collects any ammonia vol atilized from collected, semi-volatile ammonium nitrate particles. The nylon filter retains any nitric acid volatilized from particulate ammonium nitrate. Following fi eld exposure, the denuders, filters, and field data logs are sent to the CSU lab for chemi cal extraction and analysis. Total sampler air

volume from the data sheet is then us ed to calculate c oncentrations.

Table 1: Instrumentation and Monitored Parameters Boulder, Wyoming Air Quality

Station

Component Instrumentation Height Frequency Parameters

GASEOUS URG denuders 1.5m 3-day and 4- day integrated samples Ammonia, NH 3 

### Nitric Acid,

HNO 3



### PARTICULATE URG stacked filters 1.5m 3-day and 4- day integrated samples Ammonium,

NH 4 +


### Nitrate, NO 3 - 

### Sulfate, SO 4 2-



## RESULTS
Figure 1 shows a timeline of gaseous and pa rticulate concentrations from December, 2006 – January, 2008. Figure 2 plots the monthl y mean, standard deviation, minimum,

and maximum NH 3 

### concentrations. NH 3 

### concentrations are below 1 ppbv for most of the monitoring period, peaking in A ugust, 2007 at 1.55 ppbv. Elevated NH 3 

### concentrations

here coincide with warmer summer months. A shift in ammonium nitrate equilibrium toward the gas phase might be responsible for some of this increase, although an increase in total reduced nitrogen (ammonium + am monia) during the summer suggests that changes in emissions and or transport patter ns are likely also im portant contributors.

### Figure 1: Timeline of measured concentrations.

0.0 0.5 1.0 1.5 2.012/1512/2212/291/51/121/191/262/22/92/162/233/23/93/163/233/304/64/134/204/275/45/115/185/256/16/86/156/226/297/67/137/207/278/38/108/178/248/319/79/149/219/2810/510/1210/1910/2611/211/911/1611/2311/3012/712/1412/2112/281/41/111/18

date 2006-2008 NH3 (g) NH4 + (p)

HNO3 (g) NO3 - (p)

SO4 2- (p)g m-3ion / uconcentrat



### Figure 2: 2007 monthly and annual NH 3 

### concentration data

Three events stand out: high particulate NO 3 - 

### in January, 2007; high particulate NO 3 - 

### in December, 2007 – January, 2008; and high particulate SO 4 -2 

### in May, 2007. The winter

nitrate events are interesti ng as all reduced nitrogen is present as particle phase

ammonium while considerable nitric acid rema ins in the gas phase. Sufficient increases in ammonia emissions during this period could have substantially increased PM 2.5 

### concentrations by further a mmonium nitrate formation.

Figure 3 displays a timeline of the gas/partic le partitioning of the measured species for the same time period. Particulate sulfate (r ed) dominates throughout most of the year. Reduced nitrogen (green bars) shows an increased partitioning into the gas phase

### (ammonium to ammonia). Increased particulate n itrate in late winter is consistent with thermodynamic expectations: ammonium n itrate formation is favored at lower temperatures and higher relative humidities.

Figure 3: Timeline of gas-particle part itioning. Concentrations in μ g/m 3 

### , top bar stack for particles, botto m bar stack for gases.

gas-particle partitioning

-2 -1 0 1 2 312/1512/291/121/262/92/233/93/234/64/205/45/186/16/156/297/137/278/108/249/79/2110/510/1911/211/1611/3012/1412/281/111/25 start dateconcentration / ug m-3 NH4 + (p) NO3 - (p) SO4 2- (p) NH3 (g) HNO3 (g)

PM

GAS



## RESIDENCE TIME ANALYSIS
Ammonia weighted back traject ories were used to identify the geographic source areas most likely to contribute to the highest measur ed ammonia days. Back trajectory analyses use interpolated measured or modeled meteor ological fields to estimate the most likely central path over geographical ar eas that provided air to a rece ptor at a given time. The method essentially follows a parcel of air back ward in hourly steps for a specified length of time. Back trajectories account for the impact of wind direction and wind speed on delivery of emissions to the receptor, but do not account for chemical transformation, dispersion and deposition of emissions.

Trajectories were generated using the Hybrid-Single Partic le Lagrangian Integrated Trajectory (HYSPLIT) model developed by the National Oceanic and Atmospheric Administration’s (NOAA) Air Resources Labo ratory (ARL). Detailed information regarding the trajectory m odel and these data sets can be found on NOAA’s Web site ( http://www.arl.noaa.gov/ready/hysplit4.html ).

Three back trajectories we re generated per day, includ ing end times of 0400, 1200 and 2000 MST and end heights of 100 m. Each hour ly point along a 72-hour back trajectory paths was weighted with measured ammonia concentration correspond ing to the end date of each trajectory. The ammonia values a ssociated with each hourly point were then summed and normalized into 1/4 degree horizontal grid cells of latitude and longitude.

Figure 4 presents a map of the ammonia weight ed residence time for 2007. One path of

influence follows the Snake River from Idaho to the Columbia River. This is a significant

### agriculture region. Another di stinct path is from the South-Southwest along I-15 to Nevada then along the Colorado River. In addi tion to the major urban areas of Salt Lake City and Las Vegas, this pathway includes the agriculture regions of Star Valley north of Salt Lake City, the Wasatch front in Utah, and the Colorado River Basin.

Figure 4: NH 3 

### weighted residence time analysis for 2007.



## SUMMARY
A 15 month study in the Upper Green River Basin of Wyoming m easuring ammonia and nitric acid gasses and ammoni um, nitrate, and sulfate par ticles has been completed. The results of the study show that in the Upper Green River Basin of Wyoming 2007 ammonia concentrations are (1) quite variable throughout the year, (2 ) are below or near detectable limits from December through late February, (3) peak in August at 1.55 ppbv, and (4) have a yearly mean value of 0.24 ppbv. NH 3 

### weighted Residence time analysis

indicates that much of the NH 3 

### present is transported into the region from agriculture and

urban areas to the West and Southwest.

# Attachment B

Air Resource Specialists Inc. Proposed Work Scope for Ammonia and Related Gas Sampling in the Vicinity of the Navajo Generating Station

### AECOM Environment

June 2009 www.aecom.com Page 2 of 3 A ttachment B to Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station 

# Proposed ARS Work Scope for Ammonia and Related Gas Sampling in the Vicinity of the Navajo Generating Station

June 18, 2009

Overall Objective

The program’s overall objective will be to determine the background concentrations of ammonia and related gases and aerosols in northern Arizona and southern Utah for use in air quality models related to proposed actions anticipated by the Navajo Generating Station. This would be accomplished by establishing a regional monitoring site in remote areas between the Navajo Generating Station and nearby Class I areas. Due to the homogeneity of the area, we anticipate that monitoring at one site should be sufficient, and further discussions in this regard can be held with the Federal Land Managers.

Scope of Work and Assumptions

1. Equipment Procurement: ARS proposes to purcha se and configure URG 3000C dual-channel annular denuder and stacked filter samplers and support syst ems, including environmental enclosures, mounts, sample shipping cases, air temperature and barometric pressure sensors, and all other supporting components. It is assumed that the system will operate on 120 VAC line power.

2. Site Selection: ARS will join AECOM and Salt Rive r Project (SRP) representatives to plan for and select a monitoring site. It is anticipated that the siting will be complete by late Summer 2009.

3. Site Preparation and Installation: It is assumed that SRP will arrange for and perform any necessary power installations and directly pay for utility service throughout the project. ARS will travel to the site; install, calibrate, and verify instrument performance; and train the site operators. It is anticipated that installation will occur in late Summer/early Fall 2009.

4. Quality Assurance Project Plan (QAPP): A detailed QAPP of the monitoring project, compliant with EPA guidance, will be prepared by ARS in cooperat ion with AECOM. The QAPP will be distributed to appropriate state agencies and federal land managers for their review, comment, and ultimate approval.

5. Program Operation

• Duration: Winter 2009-2010 (exact duration to be discussed with EPA and FLMs)

• Sampling Strategy: It is necessary to achieve 0.15 ppb or better resolution on all samples. Ideally 24-hour samples will be taken on the EPA national 3-day schedule to allow direct comparison with other monitoring programs (i.e., IMPROVE); however , to achieve the required resolution, it may be necessary to increase the sample duration to 48 or 72 hours (centered in the EPA 3-day schedule). The final sampling strategy will be determined prior to program initia tion. Regardless of the final strategy, the program scope assumes one (1) samp le every three (3) days at each site(s).

• Laboratory Analysis: Colorado State University (D r. Jeff Collett) will prepare, ship, and receive all sample media and perform the laboratory analysis to yield the per sample concentration of NH 3, HNO 3 , NH 4 +, NO 3 -, and SO 4 --. This phase also includes all laboratory QA and field QA (i.e., lab standards, field blanks, shipping blanks, etc.), as well as all expendable media and shipping costs to
and from the site.

• Calibration, Maintenanc e, and Site Operator Support: ARS w ill perform quarterly calibrations and maintenance of the site. A repair and replacemen t parts contingency is included in this phase. CSU will travel to the site once to perform onsite quality assurance verifi cation tests. ARS will

### AECOM Environment

June 2009 www.aecom.com Page 3 of 3 A ttachment B to Conceptual Plan for Ammonia Monitoring in the Vicinity of the Navajo Generating Station provide on-demand telephone site operator support throughout the project to address sample change issues, perform QA checks and diagnostics, and perform minor repairs.

• Site Operators: A site operator will c hange sample media every three (3) days.

• Data Reporting: All laboratory results will be qu ality assured and verified. Monthly spot reports and quarterly data reports will be prepared and delivered and will include operational timelines, analyte concentration tables and plots, quality assura nce issues (i.e., blanks concentrations and corrections, detectable limits, et c.) and other narratives and products that will quantify the overall accuracy of the program. The reports will be acco mpanied by digital files of all tabular and graphic products.