Cache Valley Air Quality Studies 

A Summary of Research Conducted 

(through 2006) 

prepared by 

Dr. Randy Martin 

Department of Civil & Environmental Engineering 

Utah State University 

UMC 4110 

Logan, UT 84322 

rmartin@cc.usu.edu

August 2006 
ii

EXECUTIVE SUMMARY 

 The Cache Valley airshed is in serious threat of exceeding the U.S. National Ambient 

Air Quality Standard (NAAQS) for Particulate Matter less than 2.5 μm in diameter (PM2.5). 

Although the local airshed approaches both the annual (15 μg m-3) and the 24-hr standard (65 

μg m-3), it is the 24-hr standard that is in the greatest danger of exceedance. As of June 2006, 

the regulatory allowable 98th percentile value for 2006, roughly the eighth highest value) can 

only be 33.2 μg m-3 without exceeding the NAAQS. To date, this value has been exceeded 

four times. For comparison, the target value was exceeded 6, 41, and 39 times in the years 

2003, 2004, and 2005, respectively. It should also be noted that the U.S. EPA is currently 

considering lowering the 24-hr standard to 35 μg m-3. 

 The Cache Valley PM2.5 is somewhat uniquely a wintertime problem, when low 

lying, persistent radiation and subsidence inversions set up, trapping pollutants in the Valley 

for extended periods of time, allowing photochemically-derived particulate material to 

become elevated. Chemical analysis by researchers at Utah’s Division of Air Quality and 

Air Monitoring Center, as well as Utah State University, have shown that 50-95% of the 

PM2.5 collected at the Logan site is composed of ammonium nitrate (NH4NO3). 

 In order to understand the local pollutant behavior and identify the most appropriate 

remediation scenarios, several sequential and parallel research programs have been 

conducted by Dr. Randy Martin and others at Utah State University. This document 

summarizes these efforts and attempts to coalesce these studies into a single report. 

1) PM Homogeneity

 - Statistically (95% CI), the Cache Valley is homogeneous with regard to PM2.5

concentrations during inversion episodes, although some site-to-site variation may 

exist. The areas which trended lower in concentrations were the extreme southeast 

(Hyrum) and west (Mendon) portions of the Valley. As a partial result of these 

studies, FRM regulated monitoring stations were established in Hyrum, UT, Amalga, 

UT, Prestion, ID, and Franklin, ID. 

2) Valley Ambient Ammonia

 - Based on measurements at the Logan location, the Valley’s wintertime formation of 

ammonium nitrate was found to be limited by the availability of nitrate, specifically 

nitric acid (HNO3). The ambient Logan wintertime NH3 averaged (24-hr) 9.2 μg/m3

(13.9 ppb). Furthermore, following these data, the Cache Valley was found to be 

NH3-rich by a factor of approximately two. Comparisons of wintertime ambient NH3

concentrations between the Valley’s urban area (Logan) and a rural location 

(Amalga), showed the rural area averaged ≈2.5 times the NH3 of the urban site. 

3) On-road Automobile Emissions

 - The study found that approximately 4.5% and 10.3% of the Valley’s vehicles would 

fail inspections tests for NOx and VOCs, respectively, and that these vehicles were 

responsible for 25.4% and 47.8% of the valley-wide emissions. The study also found 
iii

that the majority of the vehicles that would fail would be older than 1996. As of 2004, 

vehicle registrations from the Utah Department of Motor Vehicles showed the 

percentage of vehicles that are 1996 or newer be 49.4%, and, therefore, eligible for I 

& M testing with the simpler on-board diagnostic (OBD) method. 

4) Public & Student Phone Survey 

 - 

5) Inversion Heights (dT/dz) 

6) Indoor/Outdoor PM2.5 Concentrationss 

7) Wintertime Vertical Ozone Profile 

8) VOCs 
iv

Cache Valley on a “good” day (Feb. 25, 2002) 

Cache Valley on a “moderate” day (Feb. 23, 2002: PM2.5 ≈ 40 μg/m3

) 

Cache Valley on a “very bad” day (Feb. 16, 2004; PM2.5 = 101.6 μg/m3

), viewed from 

adjacent 6300 ft asl ridge top 
v

Installing a portable AirMetrics’ MiniVol PM2.5 sampler 

Recovering a temperature sensor form the ridge above Logan 
vi

URG ammonia and acid gas denuder system installed at the Logan site. 

Passive ammonia samplers (with and without rain cap) 
vii

Cache Valley on-road vehicle exhaust measuremnt 

On-road “Red Day’ notification signage Main Street in Logan 
viii

MiniVol samplers during indoor vs. outdoor studies 

Teflon nozzle and tubing during ozone vertical profile flight (Feb. 9, 2006: 14:57) -- also 

note visible inversion layer 
ix

ACKNOWLEDGMENTS 

The investigators would like to thank the State of Utah and Utah State University for 

partial funding under the Community/University Research Initiative (CURI) Grant program. 

Utah’s Department of Environmental Quality’s Division of Air Quality (DAQ) and Air 

Monitoring Center (AMC) are also to be gratefully thanked for funding several different 

aspects of the studies described within this document. Additional funding for personnel and 

supplies was obtained through the Utah Water Research Laboratory (UWRL). 

The authors would also like to thank Bob Dalley, Neal Olson, Dave McNeill, Brock 

LaBaron, Tyler Cruckshank, Bruce Allen, Ran McDonald, Joe Thomas, Cheryl Heying, and 

Rick Sprott for their cooperation in supplying equipment, comparative data, and expertise. 

Personnel from the Bear River Health Department were also instrumental in the research 

described herein and are also owed a great deal of thanks and appreciation. Additional 

acknowledgements go to USU students Thomas Bradley, Hosam Jamal, and Demetrio 

Cabanillas for their participation in various aspects of this project.
x

TABLE OF CONTENTS 

EXECUTIVE SUMMARY ..................................................................................................... ii 

ACKNOWLEGDEMENTS..................................................................................................viii 

OVERALL INTRODUCTION................................................................................................ 1 

VALLEY-WIDE PM10 AND PM2.5 SATUARATION (HOMOGENEITY) STUDY............ 2 

CACHE VALLEY AMBIENT AMMONIA STUDIES ....................................................... 17 

ON-ROAD VEHICLE EMISSIONS IN CACHE VALLEY (2004) .................................... 30 

VERTICAL TEMPERATURE PROFILE MEASUREMENT............................................. 51 

INDOOR/OUTDOOR PARTICULATE MATTER IN THE CACHE VALLEY................ 59 

WINTERTIME VERTICAL OZONE DISTRIBUTIONS.................................................... 67 

REFERENCES ...................................................................................................................... 78 
1

OVERALL INTRODUCTION 

The elevated wintertime levels of PM2.5 in Utah’s Cache Valley have been the 

subject of concern since measurements of the criteria pollutant began in the spring of 

2000. As shown in Table 1, the airshed has flirted with exceeding National Ambient Air 

Quality Standard, especially the 24-hr value (65 μg m-3), since the first complete 3-yr 

data set was obtained. 

Table 1. Regulatory PM2.5 values for Logan, UT (UDAQ, 2006). 

Year Annual Average 24-hr 

98th Percentile 

2001 15.6 μg m-3 71.1 μg m-3

2002 14.7 μg m-3 58.4 μg m-3 

2003 8.4 μg m-3 31.5 μg m-3 

3-yr Avg 13.0 μg m-3 54.8 μg m-3 

2004 15.3 μg m-3 101.5 μg m-3 

3-yr Avg 12.8 μg m-3 63.8 μg m-3 

2005 13.0 μg m-3 61.7 μg m-3 

3-yr Avg 12.1 μg m-3 64.9 μg m-3 

2006 Allowable ---- 33.2 μg m-3

 Compositional research conducted by Utah’s Division of Air Quality (DAQ) and 

Air Monitoring Center (AMC), as well as investigators at Utah State University, showed 

that the bulk of the fine particulate material consisted of ammonium nitrate (NH4NO3) 

(UDAQ, 2006). During “typical” winter days, it was shown that average NH4NO3

content accounted for 50-60% of the particulate material, on elevated days (> 65 μg m-3), 

the NH4NO3 fraction approached 80-95%. 

The discovery of the elevated levels of PM2.5 in the Cache Valley motivated 

several research studies to identify the dominant causes and potential areas of 

remediation. These efforts are described within this document. Specifically, this report 

summarizes research into Cache Valley’s PM10 and PM2.5 homogeneity, determination of 

ambient levels of gas-phase ammonia (NH3) and it’s role in limiting particulate 

formation, local on-road vehicle emissions, local attitudes toward potential particulate 

control scenarios, inversion heights, indoor vs. outdoor PM2.5 concentrations, research 

into ambient (rural and urban) concentrations of volatile organic compounds (VOCs), and 

continuing research of vertical ozone profiles and indoor ammonia. 

 It should be noted that these research programs include funding through Utah’s 

DAQ and AMC, but also other sources including Utah State University, The Utah Water 

Research Laboratory, and the Bear River Health Department. 
2

VALLEY-WIDE PM10 AND PM2.5 SATURATION (HOMOGENEITY) 

STUDIES 

Contributing Authors 

Dr. Randal S. Martin 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 

Grant W. Koford 

Bear River Health Department 

Logan, UT 
3

INTRODUCTION 

Among the first projects studied in cooperation with the Utah’s 

Division of Air Quality and Utah State Universities Air Quality Research 

Group within the Department of Civil and Environmental Engineering 

(CEE) and the Utah Water Research Laboratory (UWRL) was the 

examination of the potential homogeneity of PM10, and then PM2.5, 

throughout the Cache Valley. The impetus for this study began in the fall of 

2001 with comparisons of ambient PM10 and PM2.5 as measured at the 

Smithfield, UT residence of Dr. Randy Martin and those monitored by the 

DAQ at the Logan city sampling location (approximately 11 kilometers 

apart). Figures 1 and 2 show the 2002 comparisons for PM10 and PM2.5, 

respectively.

Figure 1. Comparison of Logan and Smithfield 2002 ambient PM10 concentrations. 

Figure 2. Comparison of Logan and Smithfield 2002 ambient PM2.5 concentrations. 

2002 Cache Valley PM2.5 (Act. Conditions)

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1/ 1 1/ 31 3/ 2 4/ 1 5/ 1 5/ 31 6/ 30 7/ 30 8/ 29 9/ 28 10/ 28 11/ 27 12/ 27

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Smithfield Logan (DAQ)

2002 Cache Valley PM10 (Act Conditions)

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Smithfield Logan (DAQ)
4

As is shown above, the concentrations trends and absolute values are very similar 

for both sites, including the elevated levels recorded during the wintertime inversion 

episodes. When similar data for the 2003 calendar year are included, the correlation (R2

) 

between the two sites was 0.819 and 0.923 for PM10 and PM2.5, respectively. Although 

not statistically quantifiable, visual examination of the plotted data, for both size 

fractionations, seem to show a slight positive (greater than) difference at the Smithfield 

location in the summer and a slight negative (less than) difference in the winter. This 

could be a reflection of the somewhat more rural nature of the Smithfield location. 

Cache Valley’s high, “official” wintertime PM2.5 concentrations, as measured at 

the single Logan city sampling site, the similar PM10 and PM2.5 trends observed at the 

separate Smithfield location, the abundance of secondary material, and visual 

observations suggested that the particulate pollution was likely not an isolated problem 

centered around the Logan location, but more likely homogeneous throughout the Cache 

Valley. In order to investigate this hypothesis, five portable PM10 samplers were 

deployed throughout the Valley and operated during the winter of 2002/2003. These 

samplers were further compared to the DAQ operated Logan location and a paired set of 

federal reference method (FRM) PM10 and PM2.5 samplers deployed at the Smithfield 

site. 

As will be further discussed in following sections, the preliminary study 

conducted in during the winter of 2002/2003, at the (equipment) limited number of 

available sites, showed that the Valley’s PM10 was statistically homogeneous across the 

compared locations. Although the data did suggest overall ambient particle homogeneity, 

the unexpectedly low particulate concentrations during the examined winter (refer back 

to Table 1), the variability in the relationship between PM10 and PM2.5, and the limited 

number of available samplers left it uncertain as to whether the airshed was truly 

homogeneous with respect to PM2.5, particularly at levels above the NAAQS. In order to 

more fully investigate this question, fifteen portable PM2.5 samplers were deployed 

throughout the Cache Valley and operated during the winter of 2003/2004. Also as 

before, two federal reference method (FRM) PM2.5 samplers were also deployed, 

including the Logan UDAQ regulatory and the Smithfield PM2.5 sampling sites. 

METHODOLOGY 

2002/2003 PM10 Homogeneity (Saturation) Study 

In an attempt to bracket typical wintertime conditions, the initial PM10

homogeneity study took place from October 24, 2002 through February 26, 2003, with a 

nominal sampling frequency of every six days. The samples were targeted to run for 24 

hours, midnight to midnight, on each of the sample days. In addition to the Logan city 

sampling site (UTM 430309 E, 4619926 N, zone 12), six additional sites were established 

throughout Utah’s Cache Valley. These sites were located 2.9 km ENE (USU Campus), 

3.9 km S (Evan’s Farm/Nibley), 5.5 WNW (Cache Valley Hunter Education Center), 9.5 
5

km SSW (American Heritage West Center), 10.9 km N (Smithfield), and 17.1 km NW 

(Newton) of the Logan sampling location. 

Five portable AirMetrics PM10 MiniVol samplers (Airmetrics, 2004) were 

borrowed from the Division of Air Quality of Utah’s Department of Environmental 

Quality (DEQ). These instruments were deployed at all but the Smithfield location. At 

the time of the described study, equivalent PM2.5 samplers were not available to the 

investigators. The MiniVol Samplers operate via a battery-powered pump, which draws 

air through an impactor specifically-designed to separate the larger particle fraction (>10 

μm), allowing the PM10 material to be collected on a subsequent 47 mm Teflon filter. The 

filters were equilibrated at room temperature, in an air-tight desiccator, and weighed on a 

5-place (gram-based) balance pre- and post-exposure until triplicate weights within 0.05 

mg were obtained. 

The samplers are designed to operate at an actual flowrate of 5 Lpm, with flow 

controlled via a manually set rotameter. Prior to sampling, each system was calibrated 

using a soap-bubble meter and a calibration equation was developed relating local 

temperature and pressure and the rotameter reading to the flowrate at actual conditions. 

For a given sampling run, the expected average temperature and pressure were estimated, 

the necessary rotameter setting for the required 5 Lpm (actual) was determined, and the 

flow was adjusted so that when the system’s internal alarm initiated the sampling period, 

the proper flowrate would be obtained. An on-board elapsed time counter registered the 

actual duration of any given sampling period (some runs were abbreviated due to battery 

failure), which when combined with the rotameter flowrate, was used to determine the 

sample volume. 

At the Smithfield location, a paired set of PM2.5/PM10 FRM Samplers (Andersen 

Instruments, RAAS 2.5-100) were operated by the investigators following the basic 

regulatory guidelines outlined in 40 CFR 50, Appendix L (40CFR50, 2003). The FRM 

samplers at the Logan site, the DEQ’s official Cache Valley sampling location, were 

operated by DAQ and Bear River Health Department (BRHD) personnel, who shared the 

collected data with the project investigators. 

Furthermore, the comparability, and the necessity of any potential correction 

factors, of the portable MiniVol samplers to the FRM samplers was examined via 

separate co-located sampling runs, in addition to the scheduled sampling periods. For 

this co-located investigation, the MiniVols were placed next to the Smithfield FRM 

samplers and each was operated as normal for four separate, 24-hour sampling periods. 

2003/2004 PM2.5 Homogeneity (Saturation) Study 

As before, since Cache Valley’s PM2.5 problem is generally limited to winter 

periods, the next phase of the particle saturation study took place from November 11, 

2003 through February 27, 2004, with a nominal sampling frequency of every six days. 

A significant inversion, and accompanying PM2.5 episode, took place January 7-24, 2005 

and during this period, the samplers were operated every other day. The samples were 
6

410000 420000 430000 440000

UTM Easting (NAD27)

4600000

4610000

4620000

4630000

4640000

4650000

4660000

4670000

UTM Northing (NAD27)

Preston, ID

Cornish, UT

Clarkston

Franklin, ID

Richmond

Newton

Amalga

Smithfield Ballard

Junction

Mendon

Logan

Hunter Ed USU

Evan's

ASF Farm

Wellsville Hyrum

UT-ID

Border

targeted to run for 24 hours, midnight to midnight, on each of the sample days. In 

addition to the Logan city sampling site (UTM 430309 E, 4619926 N, zone 12), sixteen 

additional sites were established throughout the Cache Valley. The additional sites were 

located in or near surrounding Utah communities of Wellsville, Hyrum, USU’s Animal 

Science Farm (ASF), USU’s Evan’s Farm, Mendon, Cache Valley Hunter Education 

Center (Hunter Ed), the Utah State University campus (USU), Ballard Junction, 

Smithfield, Amalga, Newton, Clarkston, Richmond, and Cornish. Two sites were also 

established on the Idaho side of the Cache Valley, at the towns of Franklin and Preston. 

Figure 3 shows the various sites’ location in terms of UTM (NAD27) coordinates. 

Figure 3. Relative Cache Valley sampling locations for the 20003-2004 PM2.5 saturation 

study. 

The fifteen portable AirMetrics PM10/2.5 MiniVol samplers (AirMetrics, 2004) 

were obtained from the Air monitoring Center (AMC) of Utah’s Department of 

Environmental Quality (DEQ). These instruments were deployed at all but the 

Smithfield location. The MiniVol samplers operate via a battery-powered pump, which 

draws air through an impactor specifically-designed to separate the larger particle 
7

fraction (>2.5 μm), allowing the PM10 or PM2.5 (depending on the sample head) material 

to be collected on a subsequent 47 mm Teflon filter. The filters were equilibrated at room 

temperature, in an air-tight desiccator, and weighed on a 6-place (gram-based) 

microbalance pre- and post-exposure until triplicate weights within 0.005 mg were 

obtained. 

The samplers are designed to operate at an actual flowrate of 5 Lpm, with flow 

controlled via a manually set rotameter. Prior to testing, each system was calibrated 

using a soap-bubble meter and a calibration equation was developed relating local 

temperature and pressure and the rotameter reading to the flowrate at actual conditions. 

For a given sampling run, the expected average temperature and pressure were estimated, 

the necessary rotameter setting for the required 5 Lpm (actual) was determined, and the 

flow was adjusted so that when the system’s internal alarm initiated the sampling period, 

the proper flowrate would be obtained. An on-board elapsed time counter registered the 

actual duration of any given sampling period (some runs were abbreviated due to battery 

or pump failure, programming errors, etc.) which, when combined with the calibrated 

rotameter flowrate, was used to determine the sample volume. 

At the Smithfield location, a PM2.5 FRM sampler (Andersen Instruments, RAAS 

2.5-100) was operated by the investigators following the basic regulatory guidelines 

outlined in 40 CFR 50, Appendix L (40CFR50, 2003). The PM2.5 FRM (Rupprecht and 

Patashnick) sampler at the Logan site, the DEQ’s official Cache Valley sampling 

location, was operated by DAQ and BRHD personnel, who shared the collected data with 

the project investigators. 

Once again, the comparability, and the necessity of any potential correction 

factors, of the portable MiniVol samplers to the FRM samplers was examined through 

four separate co-located test runs. For the co-located investigations, the MiniVols were 

placed adjacent to and at the same elevation as the Logan FRM sampler and operated to 

concurrent time periods. 

RESULTS AND DISCUSSION 

2002/2003 PM10 Homogeneity (Saturation) Study 

Co-location of the MiniVol samplers with the Andersen FRM PM10 sampler 

showed the portable samplers consistently reported higher PM10 concentrations for all of 

five of the individual instruments. The overall average error was found to be +27%. As 

can be seen in Figure 4, the tested MiniVols over predicted the PM10 concentrations by 

approximately 15-40%. Given the magnitude of these percentages and the relative 

tightness of their individual confidence intervals, the final data analysis calculations for 

the describe saturation study included the appropriate individual instrumentation 

correction factors. 
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Figure 4. Average percent error for the tested MiniVol samplers when compared to a colocated FRM PM10 sampler (error bars represent the 95% confidence interval). 

A total of 18 sampling days were observed for the period between October 24, 

2002 and February 26, 2003 for the PM10 homogeneity study. Out of a potential total 

sample number of 126 samples (18 sample days x 7 sample sites), 13 (10.3%) individual 

samples were not obtained due to sampler failure or operator error. Typical explanations 

included battery failure or errors in setting of the on-board timer/alarm. Typical PM10

concentrations observed, as measured at the Logan city site, varied from 4 to 34 μg m-3. 

Although some day-to-day variations were observed in the geographical location 

of PM10 maximums, on average, the Cache Valley appeared to be quite homogeneous in 

terms of relative concentrations. However, at the 95% confidence level, the site located 

to the north of the Logan city center did show slightly lower PM10 concentrations, while 

the site at the south end of Cache Valley showed slightly higher PM10 concentrations. 

Figure 5 shows the overall average site-to-site PM10 concentration variations normalized 

to the PM10 concentrations measured at the Logan (FRM) site. In other words, on any 

given day, the PM10 concentration at any particular site was divided by the PM10

concentration measured at the Logan site. This approach was used to minimize potential 

biases when averaging all of the individual sites’ data (e.g. not allowing differences on 

“low” days to be overshadowed by variations on “high” days). Although distinct trends 

can be seen in Figure 5, with inclusion of the 95% confidence intervals (error bars), the 

overall data set shows statistically homogeneous concentrations. For example, error bars 
9

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2.0

Logan Smithfield Hunter

Education

Center

Evan's Farm Newton American

Heritage

West

USU

Avg Site PM10 Normalized to Logan PM 10

for the Smithfield and American Heritage West (AHW) concentrations overlap the 

Newton PM10 concentration error bars, which, in turn, overlap all of the remaining sites. 

However, the Smithfield and AHW error bars do not overlap, so their PM10

concentrations are statistically different from each other. 

Figure 5. Average PM10 concentrations normalized to the observed Logan PM10 (error 

bars represent the 95% confidence interval). 

Figure 6 shows the average normalized concentrations in relation to the sampling 

sites geophysical location. The contours were prepared via Golden Software’s Surfer 

mapping software using a Kriging algorithm. As can be seen, on average there appears to 

be an identifiable increase in PM10 concentrations when moving from the northern end of 

Cache Valley to the southern end. 

Paired PM10 and PM2.5 samplers were only operated at the Logan and Smithfield 

locations. From these data, it was found that the PM2.5 concentrations were an average of 

67.5% ± 6.7 (±95% CI) of the PM10 concentrations. More interestingly, the Smithfield 

PM2.5 values averaged 88.4% ± 12.0 (±95% CI) of the Logan PM2.5 values, indicating no 

significant differences between PM2.5 as measured at the two sites. This is not 

unexpected as PM2.5 is a subset of the PM10 and the smaller PM2.5 particles are much 

more likely to remain suspended in the atmosphere. For example, in still air, the settling 

velocity of a 2.5 μm diameter particle is sixteen times slower than a 10 μm diameter 

particle (Cooper and Alley, 2002). 
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Smithfield

Newton

Clarkston Richmond

Logan

Mendon

Wellsville Hyrum

USU

Figure 6. Normalized PM10 concentrations measured in northern Utah’s Cache Valley, 

Oct. 2002 – Feb. 2003. 

2003/2004 PM2.5 Homogeneity (Saturation) Study 

Co-location of the MiniVol samplers with the R&P (Logan site) FRM PM2.5

sampler showed the portable samplers generally reported similar PM2.5 concentrations. 

As can be seen in Figure 7, the tested MiniVols’ measured PM2.5 concentrations differed 

from those reported by the FRM sampler by approximately –21% to +47%. The overall 

average error was found to be a remarkable –0.9%. Given the magnitude and variability 

of these percentages and the relative tightness of their individual confidence intervals, the 

final data analysis calculations for the describe saturation study included the appropriate 

individual instrumentation correction factors. 
11

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Franklin

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Hyrum

Mendon

Newton

Preston/H.E.

Richmond

USU

Wellsville

Normailzed Ratio (to Logan FRM)

Figure 7. Average percent error for the tested MiniVol samplers when compared to a colocated FRM PM2.5 sampler (error bars = 95% confidence interval). 

A total of 22 sampling days were observed for the 2003/2004 winter sampling 

period. Out of a potential total sample number of 374 samples (22 sample days x 17 

sample sites), 80 (21.4%) individual samples were not obtained due to sampler failure or 

operator error. Typical explanations included battery or pump failure, especially during 

extreme temperature events (< -10oC), or errors in setting of the on-board timer/alarm. 

PM2.5 concentrations observed during the study, as measured at the Logan city site, 

varied from 3 to 128 μg m-3. 

Similar to the 2002/2003 PM10 homogeneity study, the Cache Valley appeared to 

be relatively homogeneous in terms PM2.5 concentrations, although some day-to-day 

variations were observed in the specific location of PM2.5 maximums and minimums. 

Figure 8 shows the average site-to-site PM2.5 concentrations on good-to-moderate days 

(<65 μg m-3) normalized to the Valley-wide PM2.5 concentrations. In other words, on any 

given day, the PM2.5 concentration at any particular site was divided by the overall 

Valley-wide PM2.5 average concentration measured on that day. This approach was used 

to minimize potential biases when averaging all of the individual sites’ data (e.g. not 

allowing differences on “low” days to be overshadowed by variations on “high” days). 

This differs from the approach used for the 2002/2003 PM10 saturation study, wherein the 
12

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Cornish

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Franklin

Hunter Ed

Hyrum

Mendon

Newton

Preston

Richmond

USU

Wellsville

Smithfield

Logan

PM2.5 Normalized to Average

concentrations were normalized to the Logan site. The new approach allowed for 

calculation of confidence intervals about the Logan site as well the other locations. 

As can be seen, on the good-to-moderate days, some site-to-site variation did 

seem to exist; however, with inclusion of the 95% confidence intervals (error bars), the 

data set shows statistically homogeneous concentrations. For example, confidence 

intervals for Hyrum and Mendon overlap Evan’s Farm and Newton PM2.5 confidence 

intervals, which, in turn, overlap the confidence intervals of the remaining sites. 

However, the Smithfield and Hyrum error bars do not overlap, so their average PM2.5

concentrations on these selected days are statistically different from each other, but not 

from the data set taken as a whole. 

Figure 8. Average PM2.5 concentrations normalized to the Valley-wide average PM2.5

concentrations on days with PM2.5 <65 μg m-3 (error bars = 95% confidence interval). 

Figure 9 shows the normalized concentrations on days with PM2.5 concentrations 

<65 μg m-3 in relation to the sampling sites geophysical location. The contours were 

prepared via Golden Software’s Surfer mapping software using a Kriging curve-fitting 

algorithm. As can be seen, there appears to be an identifiable trend of increasing in PM2.5

concentrations down the center of the Cache Valley, with the highest values recorded in 

the low population areas of Wellsville, Ballard Junction and Franklin (Idaho), as was also 

shown in Figure 8. 
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UTM Northing (N

AD27)

Preston, ID

Cornish, UT

Franklin, ID

Richmond

Smithfield

Logan USU

Newton

Mendon

Hyrum

Wellsville

Figure 9. Normalized PM2.5 concentrations measured in northern Utah’s Cache Valley 

on good-to-moderate days (<65 μg m-3). 

On “unhealthy” PM2.5 days (concentrations >65 μg m-3), the data were more 

varied (larger confidence intervals), but overall more consistent in statistical 

homogeneity. As can be seen in Figure 10, only the Amalga and ASF sites, located 

essentially in the middle of the Cache Valley, were statistically different from the average 

on these high pollution days. Similarly, only the Hyrum and Preston (Idaho) sites, on the 

far south and north ends of the Valley, were statistically lower than the average. 

However, once again, taken in its entirety, the data set shows complete statistical overlap 

or PM2.5 homogeneity. It should be noted neither the Ballard Junction or Clarkston 

samplers successfully operated during any if the high concentration episodes. Also, 

during these same periods the Newton and Hunter Ed instruments only collected one and 

two samples, respectively. 
14

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Clarkston

Cornish

Evans Farm

Franklin

Hunter Ed

Hyrum

Mendon

Newton

Preston

Richmond

USU

Wellsville

Smithfield

Logan

PM2.5 Normalized to Average

Figure 10. Average PM2.5 concentrations normalized to the Valley-wide average PM2.5

concentrations on days with PM2.5 >65 μg m-3 (error bars = 95% confidence interval). 

Similar to Figure 9, Figure 11 shows the normalized concentrations on days with 

PM2.5 concentrations >65 μg m-3 in relation to the sampling sites geophysical location. 

As can be seen, there appears to be a more centralized zone of elevated PM2.5

concentrations, but that zone encompasses much of the center of the Cache Valley and its 

main population centers. The lowest average concentrations are found in the southeast 

(Hyrum) and northwest and north (Cornish, UT and Preston, ID) corners of the Cache 

Valley. 
15

410000 420000 430000 440000

UTM Easting (NAD27)

4600000

4610000

4620000

4630000

4640000

4650000

4660000

4670000

UTM Northing (NAD27)

Smithfield

Preston, ID

Franklin, ID

Cornish, UT

Richmond

Logan USU

Hyrum Wellsville

Mendon

Newton

Amalga

Figure 11. Normalized PM2.5 concentrations measured in northern Utah’s Cache Valley 

on “unhealthy” days (>65 μg m-3). 

PM10 AND PM2.5 HOMOGENEITY CONCLUSIONS 

From the 2002/2003 PM10 saturation study, although some slight areal variations 

may exist, within in a 95% confidence interval, the wintertime PM10 concentrations 

throughout northern Utah’s Cache valley appear to be homogeneous. At the Logan and 

Smithfield sampling locations, which showed a statistically significant difference in their 

PM10 concentrations, no significant differences were observed in their PM2.5

concentrations. 

 As with the previous winter’s PM10 study, some site-to-site PM2.5 variations were 

shown to exist; however, within in a 95% confidence interval, the wintertime PM2.5

concentrations throughout northern Utah’s Cache Valley appear to be homogeneous. On 

days with 24-hr PM2.5 concentrations less then the 24-hr NAAQS (65 μg m-3), the highest 

concentrations tended towards the center of the Valley, which generally tended to 
16

correspond to the lower elevations of the local topography. On “unhealthy” days or days 

in which the PM2.5 concentrations where greater than the 24-hr NAAQS, the Valley was 

once again found to be statistically homogeneous. However, during these episodes, the 

maximum concentration area was much broader and located over most of the population 

zones on the Utah side of the Cache Valley. 

The homogeneity of the PM10 and PM2.5 concentrations indicates that the 

particulate issue is not just a problem for the main population center, Logan, but for all of 

the communities of the Cache Valley. Therefore, the solution to the problem will have to 

involve all of the surrounding communities 
17

CACHE VALLEY AMBIENT AMMONIA STUDIES 

Contributing Authors 

Dr. Randal S. Martin 

Dongzi Zhu, M.S. Env. Eng. Candidate 

Kori D. Moore, M.S. Env. Eng. Candidate 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 

R. Neal Olson 

Utah Air Monitoring Center 

West Valley City, UT 
18

INTRODUCTION 

As was mentioned in the Overall Introduction, the nominal composition of the 

PM2.5 particles in the Cache Valley is dominated by ammonium salts, with ammonium 

nitrate accounting for 50-95% of the total particulate mass. For comparison, PM2.5 in 

most rural areas in the western United States are typically dominated by total 

carbonaceous mass and crustal materials (EPA, 2003). Urban areas in the western US, 

are typically dominated by carbonaceous material; however, nitrate salts appear to be a 

significant portion of the PM2.5 in the southern California area (EPA, 2003). Both rural 

and urban areas in the eastern US are dominated by the sulfate salts, with a strong 

contribution from carbonaceous materials (EPA, 2003). 

The dominance of secondary, ammonium-based particulate material in the Cache 

Valley suggested a likely abundance of ambient gas-phased ammonia (NH3) in the local 

atmosphere. The strong dependency of the local economy on agriculture, especially 

livestock production, further supported this supposition. The most current Utah state 

economic report indicates that Cache Count, UT had total agricultural receipts in 2004 of 

$121.6 million, with 83.2% of that attributable to livestock production (UGOPB, 2006). 

The most recent data available for Franklin County, ID (2000) show that agriculture 

accounted for total cash receipts of $66.0 million, with livestock production accounting 

for 85.6% of the county’s agricultural total (Sonoran Institute, 2006). 

In order to investigate levels of ambient, gas-phase NH3 and whether NH3 is the 

limiting factor in NH4NO3 formation, an ammonia sampling station was co-located at the 

Logan city sampling site to establish overall ambient levels of gas-phase and particulatephase NH3, as well as the levels of associated anions and cations. Subsequent to this 

investigation, an additional a program was initiated in the Fall of 2004 to monitor realtime ambient ammonia concentrations at the downtown Logan, UT (urban) location, the 

site historically used for federal compliance monitoring, and a rural site, located away 

from significant, typical “city-related” pollutant sources. To be representative of the 

area, a rural site was sought out, such that it was in the proximity of locally-typical 

expected rural ammonia sources, such as small cattle operations (“mom and pop” 

dairies), working agricultural fields, and natural and constructed wetlands. The 

secondary site chosen was near Amalga, UT. The goal of the second study was to see if 

the Logan location was representative of valley-wide NH3 concentrations or if there were 

significant differences between urban and rural locations. 

METHODOLOGY 

Ambient Gas- and Particulate-Phase Ammonia and Related Ions 

The ambient gas-phase ammonia and acid sampling system was co-located at the 

Logan city sampling site and sampled on an every sixth day schedule. A URG, Inc. 

Model 3000C Annular Denuder System (ADS) (URG, 2000) was used for collection of 

24-hour averaged gas- and particulate-phase samples. The full system operates at 10 

Lpm and consists of a sharp-cut PM2.5 cyclone, followed one or two acid gas (Na2CO3-
19

coated) denuders, followed by the NH3 gas (citric acid-coated) denuder, followed by a 2-

stage filter pack assembly. For the purpose of this study, the sampling was initiated in 

October of 2002 and continued through the end of 2003. 

The NH3 collection denuders were prepared prior to exposure by coating the inner 

surfaces with a 1% citric acid solution (1.0 g citric acid, 99 ml of methanol, 1 ml 

glycerol). For acid gas collection, 1% Na2CO3 solutions were prepared from 1.0 g 

Na2CO3, 1.0 g glycerol, 50 ml double-distilled, deionized water (DDW) and 50 ml 

methanol. Glycerol was used to make the denuder surface more adhesive and prevent 

oxidation of nitrite to nitrate by ozone. Within the ADS, air was drawn through the 

cyclone for large particle removal, then through the Na2CO3-coated denuder where acid 

gases were collected, and then through the citric acid-coated denuder where NH3 (g) was 

absorbed to the walls. The air stream was then drawn through a filter pack to collect the 

particulate matter for mass and compositional determination, followed by the nylon 

backup filter. The system was enclosed in a weatherproof box, which was kept at a lower 

limit of 7 0

C if the ambient temperature was less than 70C, or 20C above ambient 

temperature if the ambient temperature was greater than 70C. The system was connected 

to a pump with an accompanying mass flow controller and a dry gas meter. The mass 

flow controller allowed precise control of airflow through the annular denuder/cyclone 

assembly. The Gallus 2000 dry gas meter (Schlumberger, Reims Cedex, France) was 

also plumbed to the system and was calibrated before use to insure precise sample 

volumetric reading. 

After exposure, the denuder tubes were separately eluted with 10 ml (NH3) and 30 

ml (acid gases) of double-distilled, deionized water. Additionally, 10 μL of concentrated 

H2SO4 was added to the NH3 extract to acidify the sample, ensuring the collected gasphase ammonia (NH3) would remain in solution as the more soluble ionic species, 

ammonium (NH4

+

). The samples were stored in the dark at 4oC until the extract 

concentrations were quantified via ion chromatography. The Dionex IC system consisted 

of the following equipment: AS 40 Automated Sampler, CD 20 Conductivity Detector, 

GP 40 Gradient Pump, Membrane Suppressor, LC 25 Chromatography Oven, and an 

IonPac® AS4A-SC (4 mm) anion column or an IonPac® CS12A cation column, AG4ASC anion guard column or CG12A cation guard column, depending on the ionic 

species of interest. 

For anion analysis from the denuder washes, a 25-μL injection loop was used in 

the IC, while for cations analysis from the denuder washes, an 80-μL injection loop was 

used; and for filter extraction cations, a 195-μL loop was used. This was because the 

concentration of filtered extraction cations was much lower than that from denuder 

washes, and a larger loop allowed injection of more sample onto IC which allowed more 

consistent peak detection. For anions analysis, DDW filtered through a 0.2 μm filter was 

used as reagent water and 1.7 nM sodium bicarbonate and 1.8 nM sodium carbonate 

solution as the eluant. Stock standard solutions of 1000 mg/L of C1-

, NO3

-

, NO2

-

, SO4

2-

were prepared from ACS reagent grade salts (Fisher, Fair Lawn, NJ). For cations 

analysis, 0.15 M H2SO4 was used as the eluant. Stock standard solutions of 1000 mg/L 

of Na+

, K+, Mg+2, Ca+2, NH4

+

 were prepared from ACS regent grade materials. 
20

Calibration curves were prepared using 1, 5, 10 mg/L (ppm) stock standard solutions and 

were verified on each working day and after approximately 20 samples. Blank and 

continuing calibration verification standards (CCV), such as 5 ppm standard anions or 

cations solutions, were tested approximately every 10 samples. Peak identification and 

data processing were performed using Dionex PeakNet Data Chromatography software 

(Version 2.0). Ambient air concentrations were calculated from the IC analytic results 

and sampled air volume. 

Urban vs. Rural Ambient Gas-Phase Ammonia Study 

This study began in November 2004 and went through April 2005, gapping the 

typical Cache Valley PM2.5 “season”. It should be mentioned that due to equipment 

problems the Logan city NH3 system, sampling did not actually begin until Dec. 7, 2004. 

ThermoEnvironmental Instruments Model 17C Chemiluminescent Ammonia Analyzers 

were installed in climate controlled sampling trailers at the Logan site (41.7309°N, 

111.8376°W, ele. 1380 m asl) and at a newly established site near Amalga, UT, 

approximately 15.1 km northwest of the Logan site, roughly near the center of the Utah 

portion of the Cache Valley. Within 3 km of the rural site are a number of agricultural 

fields, two small dairy operations (50-100 cows each), natural wetlands and an associated 

stream system, a waste lagoon, and a small cheese factory. The rural site specific 

coordinates are as follows: 41.8584°N, 111.8943°W, ele. 1355 m asl. All UTMs given 

are in NAD27 coordinates. 

At both locations, sample air was transferred into the analyzers through glass 

sampling manifolds and Teflon® tubing. The Model 17C Analyzers operate through the 

sequential measurement of NO, NO2, and NH3 via ozone initiated chemiluminescence 

and surfaced catalyzed oxidation of the ammonia. The system first measures ambient NO 

and NO2 as describe by typical federal reference method gas-phase chemiluminescence 

(40CFR50, App. F, 2006), as such the NOx data are archived and available as well as the 

ammonia. The NH3 analyzer adds an additional 775°C stainless steel converter to 

oxidize the NH3 to NO. The 17C then measures the additional system response due to 

the newly created NO, which is then reported as ambient ammonia (TECO, 2004). 

The instruments were calibrated or zero/span checked on an at least semi-weekly 

basis using commercially-purchased ammonia and zero gas standards. The instrument 

has a reported lower detectable limit of 1 ppb, a response time of 120 seconds, and a 

linearity of ±1% at ranges up to 20,000 ppb (TECO, 2004). Similar instrument 

characteristics were also reported via a separate independent study (Cowen et al., 2004). 

Additional operational details can be found at the manufacture’s website (TECO, 2006). 

RESULTS AND DISCUSSION 

Ambient Gas- and Particulate-Phase Ammonia and Related Ions 
21

0

5

10

15

20

25

10/17/2002 12/16/2002 2/14/2003 4/15/2003 6/14/2003 8/13/2003 10/12/2003 12/11/2003

Gas-Phase NH3 (ppb)

0

5

10

15

20

25

30

35

40

45

50

Logan PM2.5 (

μg m-3)

Gas NH3 conc. Logan PM2.5

Figure 12 shows the ambient, gas-phase ammonia concentrations measured at the 

Logan site from October 2002 through December 2003. The average overall 

concentration is 9.3 ppb ± 1.2 (95% CI). The minimum NH3 concentrations were around 

2.5 ppb, which were observed in the summertime, and the maximum concentrations 

approached 25 ppb, which were observed in the wintertime. This is well above what is 

typically considered tropospheric background levels (0.05 – 0.2 ppb) and compares to 

other areas of high agricultural activity (Robarge et al., 2000; Finlayson-Pitts and Pitts, 

2000). The elevated ammonia levels are not unexpected due to the enclosed nature of the 

Valley’s airshed, especially during wintertime inversion episodes, and the common 

nature of livestock production in the local region. 

Figure 12. Ambient NH3 and PM2.5 measured in Logan, Utah. 

Based primarily on the number of livestock in the Cache Valley, the Utah DAQ 

estimates daily (wintertime) emissions on the order of 4.8 metric tons (UDAQ, 2006). It 

is well recognized that current NH3 emissions algorithms are considered highly uncertain 

(CAEAAFO, 2002; CENR, 2001; FAO, 2001); however, examination of these first order 

emissions estimates can give some insight into local atmospheric photochemical particle 

formation. The Utah DAQ has also estimated daily NOx and SOx emissions at 8.3 and 

8.5 metric tons. Based on these numbers, there is easily enough available gas-phase NH3

to neutralize the emitted SOx. However, the NOx-NH3 particle conversion is more 

accurately represented as an equilibrium reaction, and as such, complete conversion 

would not be expected. Furthermore, the resultant ammonium nitrate particle formation 
22

0

2

4

6

8

10

12

Dec/02, Jan,

Feb/03

Mar, Apr, May Jun, Jul, Aug Sep, Oct, Nov Dec/03, Jan,

Feb/04

Gas-Phase NH3 ( g/m3)

is favored during cold and humid (i.e. foggy) conditions as experienced during the Cache 

Valley’s winter months. The high ambient NH3 concentrations suggest the NH3 is in 

excess and the emission estimates of all of the noted species may need to be revised. 

The concurrent PM2.5 concentrations from the Logan site are also shown in Figure 

7 and it appears that the two parameters may be correlated. Linear regression analysis 

shows only a moderate correlation (r2

 = 0.537); however, it can be said that the higher 

PM2.5 concentrations typically occurred during periods of elevated ambient ammonia. 

Further, the regression analysis proportionality constant, the “slope” term, is very nearly 

equal to unity (1.006), suggesting that in the local area, a 1 ppb increase or decrease in 

ambient NH3 would be paralleled by a similar change in the PM2.5 concentration. This is 

not to suggest that NH3 emissions, and thereby particulate ammonium nitrate, increase in 

the winter months. More likely these increases are related to seasonal decreases in the 

atmospheric mixing volume and dilution rates. 

On a seasonal basis, the winter months (Dec., Jan., Feb.) showed the highest NH3

concentrations, averaging 13.9 ppb ± 2.99 (95% CI), which was statistically different 

from the remaining three seasons (see Figure 13). The spring (Mar., Apr, May), summer 

(Jun., Jul., Aug.) and fall (Sept., Oct., Nov.) NH3 concentrations were not significantly 

different from each other. The overall average ambient NH3 concentration for these three 

seasons was 7.7 ppb ± 0.94. 

Figure 13. Seasonal variations of Cache Valley gas-phase ammonia (error bars represent 

95% confidence intervals). 
23

-- based on all three algorithms (treated equally)

0

10

20

30

40

50

60

70

80

90

100

Winter Spring Summer Fall

Percent of Samples

%HNO3 Limited %Transitional %NH3 Limited

 In order to more fully examine whether the gas-phase NH3 is in abundance or 

deficit in relation to potential formation of particulate ammonium nitrate, three separate 

algorithms were applied to the collected ionic concentration data. The models used were 

the excess NH3 model of Blanchard et al. (2000), the particulate-to-total NO3

-

 ratio 

model also by Blanchard et al. (2000), and Gas Ratio Analysis (free NH3 to total HNO3) 

model of Ansari and Pandis (1999). The details of these models, and their accuracy 

compared to more detailed atmospheric photochemical models, are given in the 

associated references, but in brief they all attempt to model the gas- and particulate phase 

ion balance. The average results of these three individual calculations can be seen in 

Figure 14. 

Figure 14. Seasonal determination of HNO3- or NH3-limited particulate ammonium 

nitrate formation. 

As can be seen, during the critical wintertime periods, the NH4NO3 formation was 

limited by the availability of ambient nitric acid (HNO3) for approximately 90% of the 

observed samples. Although not relevant to the Cache Valley’s elevated wintertime 

PM2.5 concentrations, the two of the three remaining seasons also should NH3-rich 

(HNO3-limited) atmospheres. Examination of the specific ionic concentrations and the 

particulate ammonium salts further suggest that the wintertime gas-phase NH3 is in 

excess by as much as a factor of two (2x). More complete discussion of the above 

analysis can be found in Zhu (2005), and is presently in preparation for publication in a 

peer-reviewed journal. 
24

0

20

40

60

80

100

120

140

160

180

200

11/11/04 11/25/04 12/9/04 12/23/04 1/6/05 1/20/05 2/3/05 2/17/05 3/3/05 3/17/05 3/31/05 4/14/05 4/28/05

Date

Mixing Ratios (ppb) & Logan PM2.5 (μg/m3

)

Logan PM2.5 Amalga NH3 Logan NH3

Urban vs. Rural Ambient Gas-Phase Ammonia Study 

As shown in Figure 15, the ambient NH3, as measured at both the Logan (urban) and 

Amalga (rural) sites followed similar trends and paralleled elevated and depressed 

periods with the measured PM2.5 concentrations. The Logan ammonia concentrations 

showed a moderate linear regression correlation with the collocated PM2.5 concentrations 

with an R2 value of 0.6543. The rural (Amalga) was statistically less well correlated 

showing an R2

 value of 0.4895. However, directly comparing the ambient ammonia 

concentrations between the two sites showed a correlation coefficient of 0.8255, with a 

proportionality constant of 2.5 and an intercept of 7.6 ppb (using the Logan concentration 

as the independent variable), indicating the rural ammonia concentrations were 

approximately 21⁄2 times the average urban values. 

Figure 15. Logan and Amalga ambient NH3 (24-hr avg) compared to Logan PM2.5 (24-

hr avg). 

As can also be derived from Figure 15, the Logan site recorded a maximum 24-hr 

average value 74 ppb and a minimum value of <1 ppb, with a period daily average value 

of 19 ppb. This average value is remarkably consistent with that reported by Martin and 

Zhu (2004), 14 ppb, for the Logan location over the previous two winters using the 

previously described separate, denuder tube technique. The Amalga location showed 

much higher concentrations, with maximum, minimum, and average values of 200 ppb, 1 

ppb, and 58 ppb, respectively. It is of interest to note that at the Amalga location, 1-hr 

average values >200 ppb were not unusual, particularly during strong inversion events 

and the maximum 1-hr NH3 concentration observed was 373 ppb. 
25

0

10

20

30

40

50

60

70

80

90

100

 Nov 04 Dec 04 Jan 05 Feb 05 Mar 05 Apr 05

Ammonia Concentration (ppb)

Amalga NH3 Logan NH3

At the 95% confidence interval, the monthly ambient ammonia averages at the 

rural (Amalga) site were statistically higher than the concentrations observed at the urban 

(Logan) location (see Figure 16). This difference is believed to be due to the relative 

abundance of NH3 sources near the rural location, and the increased likelihood of local 

photochemistry due to the increased presence of possible reactants at the urban site (NOx, 

VOC, etc.) due to increased nearby pollutant sources (especially automobile traffic). As 

with Figure 15, Figure 16 also shows the highest NH3 concentrations occurred in January 

and February, when persistent inversions where present and high PM2.5 concentrations 

were observed. 

Figure 16. Monthly ambient ammonia averages for Logan (urban) and Amalga (rural), 

UT. 

As can be seen in Figures 17 and 18, both the Logan and Amlaga NH3 displayed 

noticeable diurnal patterns, with maximums typically occurring the morning hours (6 am 

to 10 am MST) and the minimum usually in the mid-afternoon to early evening (2 pm to 

6 pm MST). The hour-to-hour diurnal difference appeared stronger, particularly at the 

rural location, when the ambient concentrations were at their highest in February and 

March. 
26

Average Amalga Diurnal NH3

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14 16 18 20 22 24

Time of Day (MST)

NH3 (ppb)

Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 "Apr-05"

Figure 17. Logan (urban) diurnal ambient ammonia behavior. 

Figure 18. Amalga (rural) diurnal ambient ammonia behavior. 

Average Logan Diurnal NH3

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18 20 22 24

Time of Day (MST)

NH3 (ppb)

 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05
27

Wind Direction in Degrees vs Avg NH3

0

20

40

60

80

100

120

0

45

90

135

180

225

270

315

Nov-04 Dec-04 Jan-05 Feb-04 Mar-05 Apr-05

The abundance of ambient NH3 at the rural location suggested that the site may be 

significantly impacted by an adjacent ammonia source. However, examination of 

observed NH3 concentrations as a function of wind direction showed that the ammonia 

sources in the rural location seemed ubiquitous and the concentrations were consistent 

from most wind directions (see Figure 19). Furthermore, the data, averaged for wind 

direction, show complete statistical overlap (at the 95% confidence interval) within any 

given month. It should be mentioned; however, that during February and March, the 

average observed concentrations from the east and southeast, respectively, were 

statistically higher than some, but not all, of the other wind directions. While the 

previously mentioned cheese factory is approximately 1.4 km to the south-southeast, the 

land to east is mostly pasture land, agricultural fields, and natural wetlands/river areas. 

The dominant wind directions during the study period were north or northeast and south, 

southwest, or west, roughly following the topographical confines of the valley. 

Figure 19. Amalga (rural) NH3 concentrations as a function of wind direction. 
28

AMBIENT AMMONIA CONCLUSIONS 

Concentrations of ambient gas-phase ammonia reached values as high as 25 ppb 

during winter inversions, but averaged closer to 14 ppb. The gas-phase NH3

concentrations in the two observed winter periods (2002/2003 and 2003/2004) were 

almost same, suggesting consistent pollutant wintertime emission rates and similar 

inversion-dominated pollutant trapping. Spring, summer, and fall NH3 concentrations 

were significantly lower, averaging just over one half of the wintertime levels. The data 

showed only a moderate relationship between ambient NH3 and PM2.5 (R2

 = 0.537), but 

the overall trend suggested a one-to-one rate of change between the two parameters. 

Applying an excess ammonia model, a particulate-to total-NO3

-

 model and gasratio model, showed that all the of results indicated the Cache Valley’s wintertime 

atmosphere was ammonia-rich or HNO3-limited in reference of secondary NH4NO3

aerosol formation (using the Logan site as the refence location). Since Cache Valley’s 

atmosphere has been proved to be ammonia rich, or HNO3-limited through the herein 

described study, reduction on HNO3 will produces a greater, more immediate, reduction 

of aerosol NH4NO3 than will an equivalent reduction of NH3. Programs to be 

implemented could include vehicle inspection and maintenance (I&M) programs, 

increased public transit programs, car pooling, and other programs to reduce vehicle 

miles traveled. 

 The monthly average ambient ammonia concentrations at the urban varied from 

5-31 ppb, with the highest values occurring in February and March, the same time 

periods when maximum PM2.5 concentrations were observed. The highest daily average 

observed was 74 ppb and the test period (five month) average was 19 ppb. These values 

compare well to previous investigators reported values for the Logan area (Martin and 

Zhu, 2004; Mangelson et al., 1997) and are generally much higher than those reported for 

other urban areas, with the exception on Phoenix, AZ (Watson et al., 1994) and 

Riverside, CA (Yoong, 1981). The listed two urban areas reported ambient NH3

concentrations on the same order as the Logan site. 

The nearby rural (Amalga) site showed monthly average ammonia concentrations 

of 20 to 87 ppb, with the highest values occurring during the same months as those at the 

urban site. The overall correlation (R2

) between the two sites was 0.8255, with a derived 

relationship between locations as shown in Equation 1: 

 [NH3]Rural = 2.51 * [NH3]Urban + 7.58 (Equation 1) 

where all concentrations are in parts per billion (ppb). 

 The highest daily average observed at the rural was 200 ppb and the test period 

(six month) average was 58 ppb. The maximum 1-hr NH3 concentration observed for the 

rural location was 373 ppb. These values are well above those reported for nonagricultural, rural areas (Watson et al. 1994; Pryor et al. 2001; Thoni et al. 2003), but are 
29

in line with rural sites collocated around strong agricultural production facilities (Mopunt 

et al., 2002; McCulloch et al., 1998). 

Comparison of hourly ambient NH3 concentrations with hourly averaged wind 

directions showed near complete statistical homogeneity, although there were a few 

direction-to-direction differences during the months of February and March. The 

independent nature of the ammonia concentrations in relation to the wind vectors 

suggests that the rural NH3 sources are well-dispersed throughout the Cache Valley and it 

is likely the no single source (no one point, area, etc. source) dominates the local NH3

emissions budget. It would seem more likely the high rural ammonia concentrations are 

due to a multitude of valley-wide sources. 

Additionally, as shown in Equation 1, the rural ammonia levels are on the average 

2.5x greater than the urban levels. As also mentioned above, as measured at the Logan 

site alone, was in ammonia excess by a factor of approximately two in regard to the 

photochemical formation of particulate ammonium nitrate. If indeed the Amalga location 

is representative of the other rural areas of the Cache Valley, the local atmosphere may be 

more ammonia-rich than previously assumed. This would, in turn, mean that the worth 

of potential NH3 reduction scenarios would have to be very carefully examined. 
30

ON-ROAD VEHICLE EMISSIONS IN CACHE VALLEY (2004)

Contributing Authors 

Dr. Randal S. Martin 

Mark Greenwood, B.S. Env. Eng. student 

Lisa Kent, B.S. Env. Eng. student 

Kori D. Moore, B.S. Env. Eng. student 

Clint Rogers, B.S. Env. Eng. student 

Angela Squires, B.S. Env. Eng. student 

Lisa Kent, B.S. Env. Eng. student 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 
31

INTRODUCTION 

Research described within the ammonia section of this document showed that the 

local Cache Valley ambient air is ammonia-rich during the winter months, meaning that 

the limiting compound is the nitric acid (HNO3) that combines with the gaseous ammonia 

(NH3) to form NH4NO3. Nitric acid is photchemically formed in the atmosphere from 

precursor oxides of nitrogen (NOx) compounds through a series of photochemical 

reactions involving other reactants such as ozone (O3), hydroxyl radicals (OH), reactive 

volatile organic compounds (VOCs), and available solar radiation (insolation). The main 

source of NOx and VOCs in Cache Valley is the transportation sector with over 80,000 

vehicles registered in Cache County, UT and Franklin County, ID. The Cache County 

Assessor lists approximately 67,000 motor vehicles, half of which are 1995 or older, as 

being registered within the county (Cache County, 2004). Franklin County, ID, as of 

2004, had 12,900 total registered motor vehicles of similar age structure (IDT, 2006). 

A potentially effective way to control NOx and VOC emissions is to control the 

emissions from automobiles, and this is typically accomplished through the 

implementation of an Inspection and Maintenance (I & M) Program that tests emissions 

on an annual or bi-annual basis. Vehicles that do not pass the test must be fixed before 

being allowed to register. This option for controlling pollutant emissions is currently 

being considered by Cache County, but information was lacking on what expected 

emissions of the current vehicle fleet and what fraction of the fleet may be expected to 

fail or pass an I & M Program. As such, a series of on-road emission tests were 

performed in May 2004 in and around Logan, UT. 

METHODOLOGY 

The vehicle emission testing was done using an MD-LaserTech RSD (remote 

sensing device) borrowed from Utah County. Additionally, a trained operator, Todd 

Rittle, from the Utah County Department of Health was on hand to operate and calibrate 

all of the test equipment. In brief, the system shot infrared and ultraviolet laser beams 

across a roadway, reflected of a polished mirror and returned to the transceiver, where 

wavelength-specific energy absorption was recorded. The concentrations of NOx, VOCs, 

CO, and CO2 within the vehicle plume were the instrumental correlated with the laser 

attenuation. Additional information recorded included vehicle speed, acceleration, and 

license plate data (the latter recorded via a time-marked photograph. It should also be 

noted that a beam height of approximately 14” was selected, knowing this be height was 

a choice between measurement of typical car or typical pickup exhaust heights. The 14” 

was more typical of the passenger automobile. 

The testing occurred at various roadside sites along high traffic areas throughout 

Cache Valley during the period of May 13-20, 2004. A relative map of the tested 

locations can be seen in Figure 20. Finally, the slope of the road at each site was 

subsequently measured by USU undergraduate Environmental Engineering students 

using standard surveying techniques and used to calculate a comparison parameter known 

as vehicle specific power (VSP). 
32

Figure 20. Locations of May 2004 Cache Valley on-road vehicle emissions study. 

RESULTS AND DISCUSSION 

The number of (valid) vehicles surveyed for exhaust emissions at all sites within 

Cache Valley was 12,464 at an average speed of 34.4 mph. The vehicles were separated 

into bins by vehicle year beginning with the year 1980 and continuing at five year 

increments until the last bin of 1996 and older. Figure 21 displays how the sample set of 

surveyed vehicles sorted by vehicle year compares with the total number of registered 

vehicles in the county also sorted by vehicle year. The two curves in this figure are very 

similar suggesting that the sampled data is a good descriptor of the general vehicle 

population. 

Figure 22 shows the percentage of the total bin population represented in the 

sampling set. The majority of registered cars in Cache County have a vehicle year of 

1990 or greater, and this division can be seen in Figure 22 as the 1990-95 and older than 

1996 bins had the greatest percentage of total cars sampled. 
33

Total and Sampled Vehicles

0

5000

10000

15000

20000

25000

30000

35000

40000

< 1980 1980-1984 1985-1989 1990-1995 ≥ 1996

Model Year

Number of Vehicles

0

500

1000

1500

2000

2500

3000

3500

4000

Total Vehicle Fleet Sampled Vehicles

% Sampled in each age group

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

< 1980 1980-1984 1985-1989 1990-1995 ≥ 1996

Figure 21. Vehicles surveyed with compared to total Cache County registered vehicles. 

Figure 22. Surveyed vehicles grouped by vehicle year. 

The data of exhaust emissions obtained from the surveyed cars were analyzed to 

see the percentage of cars in each vehicle year classification that would exceed the 

emission limits for carbon monoxide (CO), hydrocarbons (VOCs), and oxides of nitrogen 

(NOx). Carbon dioxide (CO2) was also monitored, but it is not reported here as it is not a 

presently regulated automobile emission pollutant. Each pollutant was evaluated 
34

<

1980

1980-

1984

1985-

1989

1990-

1995

≥

1996

Fail

0.0%

5.0%

10.0%

15.0%

Percent of 

Vehicles

Vehicle Year

Percent of Failing Vehicles for Vehicle Year for 

NOx

individually, which means that a single vehicle could potentially fail emissions testing 

based on one, two, or all three emission limits. 

Figure 23 shows the percentage of vehicles by vehicle year that would fail an 

oxides of nitrogen emissions test, based on a concentration limit 1776 ppm. As seen in 

the figure, all of the age classes are below a 15% failure rate. This means that a low 

number of cars are failing for NOx, which is the pollutant of concern for PM2.5 formation. 

The percentage of vehicles that failed on the basis of NOx is small compared to the results 

for CO and HC. Overall, 4.5% of the measured vehicles would presumably fail an 

inspection test, accounting for 25.4% of the total automobile NOx emissions. The 

average tailpipe NOx concentration measured was 396 ± 11 ppm. 

Figure 23. Percent of vehicles by vehicle year exceeding NOx emission limits.

The older cars and newer cars result in a smaller percentage of failures than 

vehicles with a vehicle year of 1980 to 1989. It can be seen from Figure 24 that once 

again the average NOx concentration for failing vehicles is not heavily dependent on 

vehicle year. 
35

0

500

1000

1500

2000

2500

3000

ppm

< 1980 1980-

1984

1985-

1989

1990-

1995

≥ 1996

Vehicle Year

Average NOx for Sampled Vehicles

Passing Vehicle Emissions Failing Vehicle Emissions

< 1980 1980-

1984

1985-

1989

1990-

1995

≥ 1996

Fail

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

Percent of 

Vehicles

Vehicle Year

Percent of Failing Vehicles for Vehicle Year for HC

Figure 24. Average passing vehicle emissions versus average non-passing vehicle emissions 

for NOx.

The data trends for hydrocarbons (VOCs) as shown in Figure 25 are similar to 

those of NOx. Older vehicle year bins have a high percentage of emission failures, while 

newer vehicles have a smaller percentage of failures. The percent of failing vehicles for 

hydrocarbons is based on a failing limit of 225 ppm. The average tailpipe VOC 

concentration measured was 99.6 ± 14.2 ppm. Overall, 10.3% of the measured vehicles 

would presumably fail an inspection test, accounting for 47.8% of the total automobile 

NOx emissions. 

Figure 25. Percent of vehicles by vehicle year exceeding VOC (HC) emission limits.
36

0

100

200

300

400

500

600

700

800

ppm

< 1980 1980-

1984

1985-

1989

1990-

1995

≥ 1996

Vehicle Year

Average Hydrocarbons for Sampled Vehicles

Passing Vehicle Emissions Failing Vehicle Emissions

From Figure 26, it can be seen that the failing vehicles emit on average 6 times 

more hydrocarbons than those that pass. Once again, the vehicle year does not have a big 

impact on the hydrocarbon concentration being emitted by the failing vehicles. 

Figure 26. Average passing vehicle emissions versus average non-passing vehicle emissions 

for VOC (HC).

Although, not relevant to Cache Valley’s PM2.5 problem, nor a CO problem, it is 

interesting to examine the vehicle fleets CO emissions with respect to the number of 

“high” emitters. Overall, the average CO concentration was 0.61 ± 0.05% (at the 95% 

confidence interval). Figure 27 shows the percentage of vehicles sampled per vehicle 

year classification that would fail emissions test based on carbon monoxide with a limit 

of 1.14% CO. In total, 11.4% of the observed vehicle fleet would fail such an emissions 

test and these vehicles were responsible for 45.9% of the total measured CO. From 

Figure 27 it can also be seen that the highest percent of vehicles that would fail according 

to year are those that are older than 1985. It also shows that less than 10% of the vehicles 

that are newer than 1995 would fail an emissions test for CO. 
37

< 1980 1980-

1984

1985-

1989

1990-

1995

≥ 1996

Fail

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

Percent of 

Vehicles

Vehicle Year

Percent of Failing Vehicles for Vehicle Year for CO

0

0.5

1

1.5

2

2.5

3

3.5

4

% CO

< 1980 1980-

1984

1985-

1989

1990-

1995

≥ 1996

Vehicle Year

Average CO for Sampled Vehicles

Passing Vehicle Emissions Failing Vehicle Emissions

Figure 27. Percent of vehicles by vehicle year exceeding CO emission limits.

From Figure 28, it can be seen that the failing vehicles appear to emit on average 

of five to seven times more CO by percentage of total exhaust than the passing vehicles. 

It is important to note that the average CO concentration for the failing vehicles does not 

vary greatly with vehicle year. The 1996 and newer cars that would fail an emissions test 

are also significant emitters like the older cars. 

Figure 28. Average passing vehicle emissions versus average non-passing vehicle emissions for CO. 
38

0

500

1000

1500

2000

2500

3000

3500

4000

Number of 

Vehicles

< 1980 1980-1984 1985-1989 1990-1995 ≥ 1996

Model Year

Projected Number of Failing Vehicles per pollutant

CO

HC

NOx

The percent of vehicles that would fail per age class for each pollutant was 

projected onto the Cache Valley fleet numbers and is shown in Figure 29. The greatest 

number of cars projected to fail emissions testing would do so because of CO emission 

violations, except in the vehicle year bin of 1980 and older, where more cars would fail 

due to VOC (HC) emission violations. The greatest number of potentially failed 

emissions tests would come from the vehicle bins 1985 through 1989 and 1990-1995. 

The percentages and totals of failing cars can not be summed because some of the 

vehicles would be counted more than once due to failing two or more emission tests. 

Figure 29. Projection of Cache County vehicles expected to fail emissions test based on CO, VOC 

(HC), and NOx emission limits. 

 It is of interest to compare the average emission concentrations of the target 

pollutants from Cache Valley to a similar study conducted in Utah County during 2003. 

These results are shown in Figure 30. As can be seen, the average automobile emission 

concentrations for NOx, VOCs (HC), and CO were all lower for the Cache County data 

set, even though an automobile I & M program is currently in place Utah County, but not 

Cache County. It should be noted from figure 30; however, that only the NOx emission 

concentrations showed a statistically significant difference (at the 95% confidence level). 

At this point, no explanation can be given for this apparent discrepancy. However, 

possible explanations could include differences in vehicle fleet structure, the possible 

inclusion of larger engine (pickup, SUV) vehicles in the Utah County study, or perhaps 

different test conditions (season, relative site locations, vehicle operating conditions). 
39

0

100

200

300

400

500

600

NOx (ppm)

PPM

Cache Utah

0

20

40

60

80

100

120

HC (ppm)

PPM

Cache Utah

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

CO (%)

%

Cache Utah

Figure 30. Average on-road vehicle emission concentration for Cache and Utah 

Counties. 

The data that was obtained for the Cache Valley has been compared to similar 

data collected in Virginia in 2003. In order to compare the Cache Valley data to Virginia 

the vehicle specific power was calculated for each vehicle that was sampled. The 

pollutant concentration was then compared to the vehicle specific power to allow a 

common term in comparing pollutant concentrations. Virginia has an existing vehicle 

inspection and maintenance program, so by comparing the average pollutant 

concentrations per vehicle specific power one can obtain an approximation of the 

reductions in emitted pollutant concentrations from the vehicles. 

 Other researchers have suggested that a parameter referred to as vehicle specific 

power (VSP) may be a relevant way to relate vehicle emissions to engine operating 

conditions. VSP is defined as the vehicle’s estimated engine power divided by the mass 

of the vehicle and is typically given in units of kilowatts per metric ton (kW/t). In 

practice, VSP can be found as using empirical relationship given by Klausmeier and 

McClintock (2003) as: 

VSP = 4.364*sin(Grade in deg/57.3)*Speed + 0.22*Speed*Acceleration + 0.0657*Speed 

+ 0.000027*Speed3

Klausmeier and McClintock (2003) reported for a Virginia study that NOx emissions 

increase with VSP until a maximum occurred somewhere between 15 and 30 kW/t, 

depending on the age of the vehicles, with the older age vehicles reaching higher 

maximum NOx emissions at lower VSP values. The Virginia hydrocarbon (VOCs) 

emission did not show as dramatic of variances with VSP; however, some decreasing 
40

VOC emissions with increasing VSP were observed particularly for older (pre 1985) age 

class vehicles 

Figure 31 shows the oxides of nitrogen emissions concentrations as compared to 

vehicle specific power for the different age classes observed in the Cache Valley study. 

The Cache Valley NOx concentrations are generally greater (≈2x) for the given range of 

VSP than the Virginia data reported by Klausmeier and McClintock (2003), where a 

vehicle I & M program is in place. This may indicate that a vehicle I & M program 

would be beneficial in reducing the amount of NOx emitted into the Cache Valley 

atmosphere by vehicles, but may also be caused by differences in vehicle fleet (although 

comparison to VSP and vehicle age should normalize that out. 

NOx vs VSP

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

-100 -80 -60 -40 -20 0 20 40 60 80 100

VSP kW/t

NOx ppm

< 1980

1980-1984

1985-1989

1990-1995

≥ 1996

Figure 31. Cache Valley vehicle specific power compared to NOx emission 

concentrations. 

Figure 32 shows the hydrocarbon (VOC) emission concentrations as compared to 

vehicle specific power for the different vehicle age classes measured during the Cache 

Valley study. Comparing the data in Figure 32 to the previously mentioned Virginia 

data, it can be shown that the Cache Valley VOC concentrations are generally 

comparable to the Virginia hydrocarbon concentrations and both data sets show relatively 

little variation of VOC concentrations with VSP. This suggests that VOCs are not a 

strong function of the engines’ workload, but rather a function of the engines’ operating 

functions. an I/M program would not be very beneficial in hydrocarbon reduction. 
41

HC vs VSP

0

100

200

300

400

500

600

700

800

900

-100 -80 -60 -40 -20 0 20 40 60 80 100

VSP kW/t

HC ppm

< 1980

1980-1984

1985-1989

1990-1995

≥ 1996

Figure 32. Cache Valley vehicle specific power compared to VOC emission 

concentrations. 

ON-ROAD VEHICLE EMISSIONS STUDY CONCLUSIONS 

From the information on registered vehicles that was obtained from the Utah 

Department of Motor Vehicles, the percentage of vehicles that are 1996 or newer was 

determined to be 49.4%. This means that approximately half of the registered cars in 

Cache Valley would be eligible for I & M testing with the OBD method. 

The results of this study have also found that the majority of vehicles that would 

fail a vehicle inspection and maintenance test would do so for hydrocarbons (VOCs) and 

carbon monoxide (CO), although the latter is not presently of concern in the Cache 

Valley, and that the majority of the vehicles that would fail would be older than 1996. 

The study indicated that approximately 4.5% and 10.3% of the Valley’s vehicles would 

fail inspections tests for NOx and VOCs, respectively, and that these vehicles were 

responsible for 25.4% and 47.8% of the valley-wide emissions. The study has also 

shown that the average pollutant concentration for failing vehicles does not vary greatly 

with vehicle year. The 1996 and newer vehicles that would fail an emissions test are 

significant pollutant contributors just like their older counterparts. 

The comparison of the Cache Valley data to a similar study conducted in Virginia 

in an area with an I & M program suggests that the NOx emission concentrations may be 

lowered with a local inspection program (based on the relationships between NOx

emissions and engine workload). A similar comparison with VOCs suggest an I & M 

program may not improve VOC emission rates.
42

CACHE VALLEY AIR QUALITY PHONE SURVEY 

Contributing Authors 

Dr. Randal S. Martin 

Mark Greenwood, B.S. Env. Eng. student 

Lisa Kent, B.S. Env. Eng. student 

Kori D. Moore, B.S. Env. Eng. student 

Clint Rogers, B.S. Env. Eng. student 

Angela Squires, B.S. Env. Eng. student 

Lisa Kent, B.S. Env. Eng. student 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 
43

INTRODUCTION 

A random public phone survey was conducted in order to understand the feelings 

of the general public concerning the air quality and potential remediation scenarios within 

Cache Valley. The survey was conducted in the Fall of 2004 by undergraduate 

Environmental Engineering students. The students randomly selected names and 

numbers from the the Cache County phone directory and called the residents until a total 

of 100 hundred response were obtained. As a separate, comparative exercise, a similar 

survey was given to the students Fall 2004 class of USU’s CEE 3610 (Environmental 

Management). 

THE PHONE SURVEY 

 The citizen phone survey began with explanation of what the survey was for and 

queried the respondent as to if they would like to participate. If they agreed they were 

asked the following ten questions: 

1) How severe is Cache Valley’s air pollution problem (not a problem, small problem, 

medium problem, large problem, severe problem)? 

2) Would you support a vehicle emission and inspection program (yes or no)? 

3) How much would you be willing to pay for an I & M program (county should pay, 

$10-$20, $20-$30, or $30-$40)? 

4) Do you think all of your cars would pass such a test (would pass, some would pass, 

would not pass)? 

5) How many vehicle and licensed drivers are in your household? 

6) What are you willing to do to reduce vehicle miles traveled (nothing, car pool, public 

transit, alternative transportation, trip consolidation, stay home) -- you may pick more 

than one? 

7) What is your home’s primary source of heating? 

8) Are there any additional sources of heating in your home? If so, what are they? 

9) Do you comply with Cache Valley’s current “No-Burn” days (not applicable, never 

comply, mostly comply, always comply)? 

10) Have you experienced a respiratory illness during Cache Valley’s elevated pollution 

episodes (yes or no)?

The student survey questions asked for the number and year of cars, what county 

each car is registered in, and what could be considered a “reasonable” price for emission 
44

Cache Valley Air Pollution Problem

17%

15%

27%

19%

22%

Not a Problem

Small 

Problem

Medium Problem

Large 

Problem

Severe Problem

inspections. The results from this survey may be more biased since all students have a 

somewhat similar background and “stage-of-life” status. 

THE SURVEY RESULTS 

The Residents Phone Survey 

The phone survey showed Cache Valley’s opinion and desires for solving the air 

quality problem. Figure 33 shows a fairly even spread of opinions concerning the 

severity of the problem. The combination of severe problem and large problem account 

up to 41% of the population compared to 32 % that believe there is no problem or a small 

problem. 

Figure 33. Q1: How severe is Cache Valley’s air pollution problem? 

Figures 33 and 34 illustrate the publics acceptance of an I & M program in Cache 

Valley and how much they would be willing to pay for it. Seventy four percent (74%) of 

the residents surveyed would support an I & M program and 54% would pay $10-$20, 

while 19% would pay $20-30$. It should be noticed that the percentage of people that 

would not support an I & M program (26%) is close to the percent of people who would 

prefer that the county tfund such a program (23%). This would likely indicate that those 

who would not support an I & M program, would prefer the county to pay for it. Figure 

35 shows that most of the surveyed residents (82%) believed all of their vehicles would 

pass and I & M test, while only 2% believed there vehicles would fail. 

Question 5 (How many vehicle and licensed drivers are in your household?) 

resulted in a ratio of 1.10 cars per licensed driver. 

 
45

Support for a Vehicle Emisions Program

74%

26%

Would Support

Would not Support

Public Acceptance of Cost

54%

19%

4%

23%

$10-$20 $20-$30

$40-$30

County Should 

Pay

Percentage of Cars In Household That Would Pass IM

82%

2%

16%

Would Pass

Would Not Pass

Some Would Pass

Figure 33. Q2: Would you support a vehicle emissions program? 

Figure 34. Q3: How much would you be willing to pay? 

Figure 35. Q4: Do you think all of your cars would pass? 
46

Percentage of People Willing to Reduce Vehicle Miles 

Traveled (VMT) through...

45%

36%

54%

40%

5%

66%

0%

20%

40%

60%

80%

Car Pool

Public Trans.

Alternate

Trans.

Trip

Consolidation

Stay Home 

None

The public’s acceptance of alternative ways to reduce Vehicle Miles Traveled 

(VMTs) was fairly evenly distributed between the presented options with only 5% of 

surveyed participants not willing to reduceVMTs (see Figure 36). This gives the County 

another option for increasing air quality in the valley by promoting items such as public 

and alternative transportation, and car pooling 

Figure 36. Q6: What are you willing to do to reduce VMTs? 

Figures 37, 38 and 39 illustrate the public’s means of heating their homes and 

compliance with county policies. Most all homes are primarily heated with a gas furnace 

(94%), while very few have a secondary source (total of 40%). Of the secondary sources, 

however, 27% were coal or wood burning stoves, the only heating source presenting a 

potential air quality problem. Of the all the people surveyed, 30% mostly complied with 

no burn policies, 11% always complied (59% were not applicable). 

The final question asked if they had ever encountered any respiratory problems 

caused by the air quality in the valley and 11% of the people said they had (see Figure 

40). 
47

Primary Home Heating Utility

94%

6%

Furnace

Other

Figure 37. Q7: What is your home’s primary source of heat?

Secondary Home Heating Utility

13%

60%

27%

Wood or Coal 

Burning Fire Place

No Extra Source Other

Figure 38. Q8: Are there any additional sources of heating in your home? 

Compliance With No Burn Days

0%

59%

30%

11% Not Applicable

Always 

Comply

Mostly 

Complies

Never 

Comply

 Figure 39. Q9: Do you comply with “no Burn” days? 
48

Number of Vehicles per Student

0

1%

1

2 49%

41%

3

6%

4

3%

Experienced an Air Pollutant Illness in Cache 

Valley

11%

89%

Yes

No

Figure 40: Q10: Have you ever experienced a respiratory illness during Cache Valley’s 

elevated pollution episodes? 

The Student Survey

The CEE 3610 Environmental Management class was surveyed with 79 students 

in attendance. The responses to the survey questions are shown in Figures 41 through 44. 

The average number of cars per student was calculated at 1.59, with one student 

responding that he/she did not own a car. 

 

Figure 41. Number of vehicles per student (% of 79 students surveyed). 
49

 

Figure 42. Student vehicles by age bin. 

Vehicle Registration Location

65% 13%

22% Cache County

Counties with I/M

Programs

Counties without

I/M Programs

 

Figure 43. Student vehicle registration location. 

Vehicles by Year

< 1980

5%

1980 - 1984

3%

1985 - 1989

13%

1990 - 1995

33%

≥ 1996

46%
50

Reasonable Price Responses

74%

16%

0%

10%

$10 - 20

$20 - 30

$30 - 40

County pays

 

Figure 44. Student responses to reasonable I & M costs 

The student survey results varied from public phone surveys in responses to cost 

for an I & M program. Seventy four percent (74%) of students agreed to pay $10-$20 for 

a program would be reasonable, while the public percentage was 54% (refer to Figure 34 

and 44). This could possibly be due to the average student income is significantly lower 

than the public average. 

The number of vehicles used per student (not vehicles per licensed driver) can be 

evaluated in that, the majority of students (49%) used only one car and the next largest 

category being two cars. This can be explained by the percentage of married and single 

students in USU’s engineering program. It can likely be assumed that the percentage of 

students with two cars are married (vehicles/ driver = 1) and the single students have only 

one vehicle. The age of vehicle distribution between students and the general public are 

almost identical 

SURVEY CONCLUSIONS 

Based on the above survey, the Cache County residents believe a significant air 

quality problem exists in the Cache Valley (68%) and are in support of a vehicle 

inspection and maintenance programs (54%). Furthermore, they would be willing to pay 

$10-20 for this service (74%). The public is also willing to take other measures to cut 

down on vehicle miles traveled in order to cut down on vehicle pollution. These 

measures include trip consolidation (66%), alternate transportation (54%), and car 

pooling (45%). 
51

VERTICAL TEMPERATURE PROFILE MEASUREMENT 

Contributing Authors 

Dr. Randal S. Martin 

Kori D. Moore, B.S. Env. Eng. student 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 
52

INTRODUCTION

 In order to better understand the inversions that occur in Cache Valley, small 

HOBO® H1 temperature sensors/data loggers were deployed beginning in the spring of 

2003 at selected elevations along an east-west transect from the valley floor up a steep 

mountainside to a point above the expected inversion heights. Through the use of the 

data loggers, the establishment, growth, and duration of inversions within Cache Valley 

were monitored over the period of one year. Data analysis shows the presence of lowlevel radiation inversions with diurnal and seasonal variations in the shape, steepness, and 

longevity of the vertical temperature profile. Comparison with measured PM2.5 values 

has shown a strong correlation between the duration of a temperature inversion and the 

ambient PM2.5 concentration. 

Background

 Cache Valley is part of the transition between the basin and range topography of 

Nevada and Utah and the mountainous topography of the Rocky Mountains. It has a total 

area of about 300 square miles. Cache Valley is bounded on the west, south, and east 

sides by mountains and by hills on the north. The valley floor has an average elevation of 

4500’ asl, and the surrounding mountains reach a height of 9900’ asl. The surrounding 

topography essentially creates a protected pocket or bowl of Cache Valley. 

 In a normal vertical temperature profile of the atmosphere just above the earth’s 

surface, temperature decreases with increasing altitude. In such conditions, turbulence 

and wind can readily mix a given pollutant throughout the vertical profile. A temperature 

inversion, on the other hand, is a positive change in temperature with increasing altitude, 

or can be defined as a layer of lighter, warmer air on top of a layer of more dense, colder 

air. The warm air essentially places a cap on the lower air, trapping below the colder air 

and any pollutants therein. If the inversion persists, the concentration of pollutants in the 

trapped layer of colder air increases as more pollutants are added (Masters, 1998). 

An example of an inversion is shown in Figure 45, obtained by driving up a 

canyon adjacent (east) to Cache Valley. There is a strong temperature inversion at about 

5000’ asl for both sampling periods. Two important things to note are that the sampling 

dates occur during the winter and that they are two years apart, suggesting the 5000’ asl 

mark is a common inversion depth. In Cache Valley, winter-time temperature inversions 

occur due to the reflection of the sun’s energy by the snow, which allows the air above to 

warm up faster than the snow covered ground, thus creating a positive change in 

temperature with increasing altitude at a point above groundlevel. High pressure cells 

create extended periods of clear skies, and these clear skies combine with snow cover 

(high albedo) to produce strong temperature inversions over Cache Valley that can last 

for several days (see Figure 46). The surrounding topography contains the colder air 

trapped below, much like air trapped in a closed jar. Pollutants released within the valley 

become concentrated, often causing a haze. A low pressure front is required to break a 

persistent inversion, and the precipitation that sometimes follows clears the air of most of 

the particulate matter. 
53

Cache Valley Vertical Temperature Profile

4500

5000

5500

6000

-12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0

Temperature (C)

Elevation (ft asl)

1/24/2002 1/12/2004

Figure 45. Temperature profile of Cache Valley obtained by driving up 

an adjacent canyon.

METHODOLOGY 

 Typical measurements of temperature inversion heights, persistence, and growth 

are achieved through the periodic release of radiosondes or the use of a tethersonde 

(Arya, 1999). A radiosonde consists of a small, light-weight radio transmitter connected 

to temperature, pressure, and humidity sensors that are all attached to a helium-filled 

balloon. The balloon is released, and, as it ascends into the atmosphere, the radio 

Figure 46. Cache Valley inversion as seen from an adjacent mountainside (ele. 

6300’ asl). The city of Logan, UT is faintly seen in the center. 
54

transmitter sends the measured data back to a receiver connected to a computer which 

interprets the data and stores it. A tethersonde differs from a radiosonde in that the 

balloon is attached to the ground via a tether. Sensor/transmitter systems may be 

dispersed along the tethering line, and may be used for longer periods of time than with a 

radiosonde. These methods provide very time-limited data, are time intensive, and 

require costly equipment. Other methods of obtaining inversion measurements include 

the use of acoustic and thermal adsorption techniques, which provide more time resolved 

data, but require complex and expensive equipment and can be time-intensive. 

There are currently several commercially available temperature sensors/data 

loggers that have been developed for both scientific and commercial uses (Whiteman et 

al., 2000). One such data logger, the HOBO® H1 (Figure 47) developed by Onset 

Computer of Bourne, MA, is a small, inexpensive unit 

consisting of a circuit board in a plastic case; waterproof 

cases are available for protection from water and sunlight. 

A similar product of Onset Computer, the HOBO® H8 

Pro was found to be effective and accurate for 

meteorological applications by Whiteman et al. (2000). 

These systems require minimal attention and have a userfriendly software program. The HOBO® H1 data loggers 

were used to measure temperature inversion 

characteristics in Cache Valley. 

Nine HOBO® H1 temperature sensor/data loggers were utilized to record ambient 

temperatures at separate locations and elevations. The sensors/data loggers were first 

calibrated to one another through the use of four co-located sampling periods. Derived 

calibration equations were used to adjust each respective data set. Since the data 

collected were only compared to one another to obtain relative temperature differences 

and not to obtain the actual temperature, it was not necessary to calibrate the sensors/data 

loggers with a Hg-thermometer. The sensors measured the temperature on a continuous 

basis, and the hourly average temperature was stored as a data point. The data were 

collected every six to eight weeks. The temperature sensors within the protective case 

were placed 2-3 meters above ground and in open areas to minimize terrestrial heating 

and ensure ventilation, respectively. The elevation of each sensor was based upon site 

accessibility and vertical spacing, and the final elevations are as follows: 4562’, 4646’, 

4865’, 5024’, 5338’, 5513’, 5735’, 6287’, and 6576’. 

RESULTS

 

The HOBO® H1 temperature sensors/data loggers obtained reliable data that were 

used to determine the characteristics of temperature inversions in Cache Valley. As a 

whole, they adequately measured the actual ambient temperature when compared with 

available, nearby meteorological stations. 

Figure 47. HOBO® H1 

temperature sensor/data 

logger and protective case.
55

March 7-31, 2003 Hourly Avg Temp Profiles

4500

5000

5500

6000

6500

7000

0 2 4 6 8 10 12 14 16

Temperature (C)

Elevation (ft asl)

3:00 AM 6:00 AM 9:00 AM Noon

3:00 PM 6:00 PM 9:00 PM Midnight

Figure 48. Average vertical temperature profile of Cache Valley for 

March 7-31, 2003. 

The use of vertical temperature profiles averaged over a period of weeks or a 

month provides a good indication of the existence and characteristics of inversions, as 

can be seen by the average values for March 2003 in Figure 48. At 6:00 AM, just before 

the sun rises, there is a strong temperature inversion between about 4500’ and 5400’, but 

above that the temperature profile looks normal, except a possible existence of an upper 

level inversion at 6300’. After the sun rises, the valley floor begins to warm up, and by 

9:00 AM the inversion is almost gone. As the day progresses, the valley increases in 

temperature and at about 3:00 PM the temperature profile almost mirrors the dry 

adiabatic lapse rate shown by the black dotted line. As the sun sets, the valley cools at a 

much faster rate than the air mass above, causing a temperature inversion to begin 

forming again before midnight. The cooling continues through the night as the diurnal 

evolution of the temperature profile comes to an end, completing the daily cycle. Also, 

note the broad range of temperature values over the entire profile. Similar results were 

produced through the analysis of data for spring, summer, and fall months. 

On the other hand, if the averaged temperatures for the first half of January 2004 

are examined, it is apparent that the temperature inversion doesn’t form and break up 

each day, rather it is more diurnally consistent (Figure 49). Only during the warmest 

times of the day is the inversion seemingly affected by the surface warming. The range 

of temperatures throughout the vertical profile is also much smaller than that of March 

2003, especially at higher elevations. This would suggest that winter months have more 

persistent inversions, as the first of January 2004 demonstrates. 
56

The data collected from the HOBO® sensors also proved very useful in examining 

the day to day changes in the temperature inversion. This day to day change can be seen 

for the month of January 2004 in Figure 50, with red representing warm temperatures, 

getting brighter as the temperatures grow warmer, and blue representing cold 

temperatures, growing brighter as the temperature decreases. It should be noted that the 

value of 2 is the first number on the x-axis, but it really represents midnight between 

January 1st and 2nd; there is not a day 32, instead it is midnight of the 31st. Early in 

January, data from the lowest sensor were not available, causing the blue patch on the 

bottom until the 18th. 

From Figure 50, it can be seen that during the first couple of days of January 

2004, it was fairly warm and no inversion was observed, or the cold air was above the 

warm air. However, the air temperatures dropped over several days and on about the 6th

a temperature inversion began to appear, with warmer air above cooler air. As time 

progressed, the temperature difference between the air masses above and below 

increased, causing the temperature inversion to strengthen and become deeper. Just after 

the middle of the month, a couple of weak low pressure cells passed through the region, 

decreasing the temperature difference, but not completely breaking up the Cache Valley 

inversion. The inversion began building after each frontal system on the 18th and the 

23rd. At the end of the month, a strong low pressure cell, with an accompanying snow 

storm, moved in to break up the inversion and provide some relief from the 20-day 

capping lid sitting over Cache Valley. The temperature profile returned to normal with 

cooler air above and warmer air below. 

Figure 49. Vertical temperature profile over 

Cache Valley for January 1-17, 2004. 

Avg Temp Profile for January 1-17, 2004

4500

5000

5500

6000

6500

7000

-16.0 -14.0 -12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0

Temperature (C)

Elevation (ft asl)

3:00 AM 6:00 AM 9:00 AM Noon

3:00 PM 6:00 PM 9:00 PM Midnight
57

Figure 50. Temperature contour map of the air above Cache Valley with respect to 

elevation and time for the month of January 2004. 

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

January 2004

4600

4800

5000

5200

5400

5600

5800

6000

6200

6400

6600

Elevation (ft asl)

 

 The temperature contour map clearly shows the growth and persistence of the 

inversion layer. To examine the affects of an inversion on the pollution concentration, 

the PM2.5 concentrations for the month of January 2004 were overlaid on the temperature 

contour map in Figure 51. The solid yellow line represents the ambient PM2.5

concentration as measured at the Logan city sampling location and the dotted green line 

represents the National Ambient Air Quality Standard (65 μg/m3

). The concentration of 

ambient PM2.5 began fairly low, but as the temperature inversion started and 

strengthened, the concentration reached values double the national standard. 

Concentrations dropped when the inversion layer begins to break up due to the two weak 

low pressure systems, but continued to increase after each system passed. It was not until 

the strong low pressure system passed through at the end of the month that the PM2.5

concentrations dropped below the NAAQS. 
58

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

January 2004

4600

4800

5000

5200

5400

5600

5800

6000

6200

6400

6600

Elevation (ft asl)

65 μg/m3

Figure 51. January 2004 temperature contour map with PM2.5 concentration (yellow) and 

National Ambient Air Quality Standard (green). 

CONCLUSIONS

The HOBO® H1 temperature sensors/data loggers were able to distinguish 

differences in the Cache Valley vertical temperature profile, including the evolution of 

temperature inversions. Despite being ground-based, the sensors/data loggers were 

sensitive and accurate enough to produce reliable data. Through data analysis, it was 

been found that diurnally fluctuating inversions dominate the vertical temperature profile 

for all but the colder months of winter, such as December, January, and February. The 

sensors/data loggers proved extremely useful in understanding the evolution of persistent 

inversions that occur in Cache Valley, as well as clearly demonstrating their effects on 

ambient PM2.5 concentrations. This understanding will allow for better prediction of high 

pollution events and, therefore, aid in current and future pollution prevention efforts. 
59

INDOOR/OUTDOOR PARTICULATE MATTER IN THE CACHE 

VALLEY 

Contributing Authors 

Dr. Randal S. Martin 

Kori D. Moore, B.S. Env. Eng. Student 

Vishal Doshi, M.S. Env. Eng. Candidate 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 
60

INTRODUCTION

The health concern for PM2.5 is because the particles are small enough to be 

breathed into the deep lung tissue and become deposited. Larger particles are filtered out 

in the nose and throat. The affects of the deposited particles depend on particle 

composition, dose, and the current health status of the individual. Daily (24-hr) averaged 

PM2.5 levels as high as 133 and 138 μg/m3 in the Cache Valley have been recorded 

during prolonged wintertime temperature inversions. Such high levels are strictly a 

winter-time problem for Cache Valley, as can be seen in Figure 52. During the spring, 

summer, and fall, the average is around 10 μg/m3

. As previously discussed in earlier 

sections, chemical analysis of the PM2.5 in Cache Valley has shown that it is dominated 

by ammonium salts, which contribute 60-90% of the total particle mass, and that 

ammonium nitrate (NH4NO3) is the largest fraction by mass (Martin and Zhu, 2004; 

UDAQ, 2006). Ammonium salts are secondary pollutants as they form in the atmosphere 

through photochemical reactions, such as is generalized in the following: 

 NH3 (g) + HNO3 (g) ÅÆ NH4NO3 (s) (Equation 1) 

As this is an equilibrium reaction, temperature greatly affects the formation, or 

dissociation, of ammonium nitrate, causing a difference in Keq values of greater than two 

orders of magnitude between 0 and 20oC. Solid particles are favored at cold temperatures 

and gases are favored at warm temperatures (Seinfeld and Pandis, 1998). 

0

20

40

60

80

100

120

140

1/1 1/31 3/1 3/31 4/30 5/30 6/29 7/29 8/28 9/27 10/27 11/26 12/26

μg/m3

2001 2002 2003 2004

Annual Average PM2.5 Standard

24-Hr PM2.5 Standard

Figure 52. Cache Valley PM2.5 concentrations as recorded for 2001-2004. 
61

The average adult begins to feel the health affects of PM2.5 at 65 μg/m3

, but those 

with compromised immune systems such as children, the elderly, and the ill may have 

noticeable affects at 40 μg/m3

. The Bear River Health Department (BRHD), in 

conjunction with the Utah Department of Air Quality (DAQ), has developed a public 

notice system to alert citizens of Cache Valley of the current air quality during winter 

months using the following color scale: “green” – good air quality, continue activities as 

normal; “yellow” – poor air quality, reduce vehicle mileage and those with compromised 

immune systems are recommended to remain indoors; “red” – bad air quality, reduce 

vehicle mileage and everyone is recommended to remain indoors. The PM2.5

concentrations that divide green and yellow and yellow and red are 40 and 65 μg/m3

, 

respectively. The BRHD also suggests that school children remain inside during recess 

and lunch time on red days. However, the quality of the indoor air, with respect to PM2.5, 

in comparison to the ambient air quality in the area schools was unknown. Therefore, it 

was also unknown if it was actually better to keep the children inside on high pollution 

days. This study was designed to determine the indoor air quality and answer the 

question as to whether it is best to keep the children inside or not. 

Past research on indoor air quality versus outdoor air quality has shown that 

indoor PM2.5 is usually less than outside, ambient levels. Sawant et al. (2004) found that 

indoor:outdoor ratios of PM2.5 concentrations in schools in Mira Loma, CA during the 

fall of 2001 and winter of 2001-2002 averaged 38%. Chemical analysis further showed 

that the highest portion of PM2.5 was organic carbon and that the indoor:outdoor ratio of 

nitrate was the smallest of all the chemical species (Sawant et al., 2004). El-Abssawy 

(2003) confirmed that indoor particle concentrations were dependent on outdoor particle 

concentrations, indoor activities, and on particle size. 

Based on these past studies and owing to the dominance of ammonium nitrate in 

the local PM2.5, it was expected that local PM2.5 concentrations would be lower indoor as 

compared to outdoor. Therefore, a study was initiated to examine any such differences. 

METHODOLOGY 

Three elementary schools and one high school in Cache Valley were chosen as 

sampling sites. Filter-based sampling was conducted using 0.45 μm Teflon filters with 

AirMetrics MiniVol impaction samplers. Paired samplers were placed both inside and 

outside of each school, as seen in Figure 53, and operated at simultaneous times to obtain 

comparable data. Sample times were during school hours, Monday through Friday from 

8:00 AM to 4:00 PM local time and were collected over two to four day periods. Table 2 

lists the school name, the location of both samplers, and the sampling dates. The UDAQ 

sampling site is located one block from Logan High School. The filters were analyzed 

for mass by comparing average pre-weights and post-weights. Anion chromatography 

was performed on solutions of the collected particles for nitrate (NO3

-

), sulfate (SO4

-

), 

nitrite (NO2

-

), and chloride (Cl-). 
62

Airmetrics MiniVolTM Portable Air Sampler

Figure 53. PM2.5 samplers at Greenville Elementary a) in the library and b) on the roof. 

School Sample Dates Sampler Location 

Greenville Inside Library 

Elementary 

Jan. 24, 2005 – 

Feb. 18, 2005 Outside Roof 

Summit Inside Library 

Elementary 

Jan. 11, 2005 – 

Feb. 11, 2005 Outside Roof 

Sunrise Inside Library 

Elementary 

Jan. 11, 2005 – 

Feb. 8, 2005 Outside Roof 

Inside Classroom Logan High 

School 

Feb. 9, 2005 – 

Feb. 25, 2005 Outside UDAQ Sampling 

Site 

Table 2. Sampling locations and dates by school. 

RESULTS AND DISCUSSION 

 The results of the mass concentration analysis from both the indoor and 

outdoor samplers for each school are shown in Figure 54. The linear fit and R2

 value for 

each data set are also shown. Examination of the data show that while outdoor PM2.5
63

Figure 54. Indoor air quality versus outdoor air quality for all four schools. 

Indoor vs. Outdoor PM2.5 Concentrations

y = 0.1557x + 11.286

R2

 = 0.5088

y = 0.0765x + 6.2655

R2

 = 0.2436

y = 0.1403x + 5.7243

R2

 = 0.9724

y = 0.0427x + 10.286

R2

 = 0.0856

0

5

10

15

20

25

0 10 20 30 40 50 60 70

Ambient PM2.5 (μg/m3)

Indoor PM2.5 (μg/m3

) Summit Sunrise Greenville

Logan H.S. Linear (Summit) Linear (Sunrise)

Linear (Greenville) Linear (Logan H.S.)

levels nearly reached the 24-hr NAAQS of 65 μg/m3, the indoor concentration at each of 

the four schools was well below the 40 μg/m3

 at which sensitive populations are 

suspected to be affected. In the data for Logan High School, one apparent outlying value 

caused a low R2

 value, but the data are otherwise well grouped. Without the outlier, an 

R2

 value of 0.5747 would be produced. The low slope values in the linear fit equations 

suggest that the indoor PM2.5 is slightly affected by the outside concentration, but that 

most of the PM2.5 is apparently removed. 

The average measured ambient and indoor PM2.5 concentrations are shown in 

Figure 55, along with the ratio of the indoor levels to the outdoor levels as a percent. The 

error bars show the 95% confidence intervals for each average value. The average 

outdoor concentrations for each school were not found to be statistically different from 

one another. The high variability seen in the outdoor values is expected due to changes 

in ambient temperatures and in the vertical mixing ability of the ground-level air mass 

caused by vertical temperature inversions, and by deposition of the particles during 

precipitation events. The indoor PM2.5 concentrations are fairly constant as demonstrated 

by the low variability. Sunrise Elementary, Greenville Elementary, and Logan High 

School indoor averages were statistically the same, but Summit Elementary had a 
64

Concentration and Ratio Averages

0

10

20

30

40

50

60

70

80

90

Ambient Indoor I:O Ratio

Conc. ( g/m3) or I:O Ratio (%)

Summit Sunrise Greenville Logan HS

Figure 55. Average PM2.5 levels and indoor:outdoor ratio by school. 

statistically significant higher average concentration than the other three. Summit 

Elementary also had the highest average indoor:outdoor concentration ratio at 61.2%. 

This, however, was not statistically different than the average for both Greenville 

Elementary and Logan High School. The average indoor:outdoor concentration ratio for 

Sunrise Elementary was not statistically different than the averages for Greenville 

Elementary and Logan High School, but was significantly different from the average of 

Summit Elementary. 

It is believed that the mechanism used by the heating system in each school may 

affect the indoor PM2.5 concentrations. Greenville Elementary, Sunrise Elementary, and 

Logan High School heat the buildings by passing air through a heater and blowing the 

heated air throughout the building (central heating). Summit Elementary uses steam 

heaters to heat the air in some of the rooms, producing less air circulation than the other 

schools. Circulation of the heated air provides a more uniform air temperature and mixes 

suspended particles more uniformly as well. As mentioned earlier, air temperature 

greatly affects the formation and volatilization of ammonium nitrate. The difference in 

heating mechanisms between Summit Elementary and the other three schools would have 

an affect on the total particle mass due to the volatilization of ammonium nitrate. 

The chemical analyses of the particles collected on the filters through anion 

chromatography confirmed that nitrate dominates the outdoor particle composition 

(Figure 56). It also revealed that the average concentration of NO3

-

 in the indoor air of 
65

Figure 56. Anion concentrations in indoor and outdoor PM2.5. 

Average Anion Concentration and Indoor:Outdoor Ratio

0

1

2

3

4

5

6

7

8

9

Chloride Nitrate Sulfate

Concentration (μg/m3) or Ratio

Indoor Outdoor I:O Ratio

the three elementary schools was six times less than the outdoor concentrations, 

producing an average indoor:outdoor nitrate concentration ration of 17%. The indoor and 

outdoor nitrite (NO2

-

) levels were below the method detection limit. The particulate 

concentration of Cl-

 was twice as high indoors as outdoors, which could be due to sources 

within the building. The SO4

-

 concentrations were much closer than either the NO3

-

 or 

the Cl- with an average indoor:outdoor ratio of 85%. Cation chromatography was not 

performed because the complimentary cation for SO4

-

 and NO3

-

 is believed to be 

ammonium (NH4

+

). The differences in the indoor:outdoor particle composition ratios 

between elementary schools is found in Figure 57. Due to the dominance of ammonium 

nitrate in the particle mass, only the NO3

-

 anion indoor:outdoor ratio was examined. The 

error bars represent the 95% confidence interval. The average indoor:outdoor NO3

-

 ratios 

are not statistically different with the small number of data points collected, but there 

appears to be an higher concentration trend in data collected at Summit Elementary, the 

school that uses steam heaters to heat the building. More data collection at all sites is 

required to more completely quantify any difference in NO3

-

 levels. 
66

Figure 57. Average nitrate indoor:outdoor ratios for the Elementary 

Schools

Average Nitrate Indoor:Outdoor Ratio for 

Elementary Schools

Summit Sunrise Greenville

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Ratio

CONCLUSIONS

 Winter-time PM2.5 concentrations above the national standard in Cache Valley 

have led area schools to keep children inside during recess and lunch time on “red” days 

as suggested by the Bear River Health Department. Indoor PM2.5 concentrations versus 

ambient PM2.5 were studied in four area schools and chemically analyzed in order to 

quantify indoor concentrations and particulate composition. 

The average measured indoor PM2.5 concentrations at the four schools was 12.5 

μg/m3, well below the 40 μg/m3 level at which children start to be affected, even when 

ambient concentrations approach and exceed the national standard of 65 μg/m3

. Anion 

analysis of the collected particles confirmed that ammonium nitrate is the dominant 

chemical species in ambient PM2.5, but the indoor NO3

-

 concentrations are on average 

17% of the outdoor concentrations. This difference in NO3

-

 concentrations is likely due 

to ammonium nitrate volatilization as the temperature increases from ambient 

temperature to room temperature. The indoor PM2.5 levels were, therefore, found “safe” 

in all four schools at the ambient concentrations measured. Keeping the children inside 

during high pollution days was in their best interest and protected them from exposure to 

unhealthy levels of particulate matter. 
67

WINTERTIME VERTICAL OZONE DISTRIBUTIONS 

Contributing Authors 

Dr. Randal S. Martin 

Crystal Viator, B.S. Env. Eng. Student 

Dept. of Civil & Environmental Engineering 

Utah State University 

Logan, UT 
68

INTRODUCTION 

Research discussed in previous sections showed that the main contributor to the 

PM2.5 in the Cache Valley was photochemically derived ammonium-nitrate (NH4NO3). 

Along with the precursor compounds of ammonia (NH3) and oxides of nitrogen (NOx), 

the formation of ammonium-nitrate is fueled by ozone and sunlight. Although 

considerably more reactions are involved, Equations 1-4 show the basic NH4NO3

formation mechanisms. 

 O3 + sunlight → O1D + O2 (Eq 1) 

 O1

D + H2O → 2OH (Eq 2) 

 OH + NO2 → HNO3 (Eq 3) 

 HNO3 + NH3 → NH4NO3 (Eq 4) 

As shown above ozone (O3) reacts with available incoming solar radiation (insolation) of 

about 310 nm, or less, to form O singlet D (O1

D), an excited oxygen atom, as well as 

diatomic oxygen (O2). The O1D then reacts with water vapor to form two hydroxyl 

radicals. Hydroxyl radicals are highly reactive and readily combine with any available 

nitrogen dioxide (NO2), produced from car emissions and other combustion sources, to 

give nitric acid (HNO3), which when combined with gas-phase ammonia forms NH4NO3. 

Furthermore, ozone is known to accelerate the oxidation of hydrocarbons and other 

pollutants in quantities as low as 20 ppb which can complicate and accelerate the above 

reactions (Woods Hole, 2006). 

 Ozone is also the product of a complex series of reactions strongly dependent on 

available sunlight (≤420 nm) as summarized in Equation 5: 

NO2 + NMHCs + sunlight → O3 + products (Eq 5)

where NMHCs represents non-methane hydrocarbons. Typically these reactions are 

expected to be dominant in the summertime when there is plenty of available sunlight. 

However, Cache Valley’s global location (41.8°N) and frequent wintertime clouds, 

storms, and fog episodes, were not thought to allow enough insolation to produce enough 

ozone or to adequately drive Equations 1 and 5. 

 Uncertainty in the local wintertime ozone levels led investigators (Dr. Martin) to 

establish an ozone monitoring site in downtown Logan, situated in the heart of Cache 

Valley, from February to April of 2004. Previously, ozone had only been monitored in 

Logan for regulatory purposes by the Utah Division of Air Quality (UDAQ) during the 

summer months; however, since the brief study of Martin, the UDAQ has established 

year-round ozone monitoring at the specified location. As shown in Figure 58, 

wintertime ozone concentrations peaked as high as 70 ppb, with average peak values 
69

0

10

20

30

40

50

60

70

80

1/30 2/4 2/9 2/14 2/19 2/24 2/29 3/5 3/10 3/15 3/20 3/25 3/30 4/4 4/9 4/14 4/19 4/24 4/29

Ozone (ppb)

Ozone Daily O3 Avg

around 45-55 ppb. The overall daily averages were on the order of 25-35 ppb. These 

unexpectedly high wintertime ozone values indicate sufficient oxidation potential to 

initiate the previously discussed reaction pathways toward ammonium nitrate formation 

(Refer to Equations 1-5). 

The source of the observed high concentrations of O3 was still uncertain, 

particularly in regards to the lack of available insolation. However, somewhat in support 

of these high wintertime values Lefohn et al. (2001) reported finding hourly average 

ozone concentrations greater than or equal to 50 and 60 ppb during photochemically 

quiescent months in the winter and spring at several rural sites across southern Canada, 

the northern United States (Wyoming), and northern Europe. 

Figure 58. Logan O3 February-April 2004. 

 For the Cache Valley situation, it was speculated that free tropospheric ozone 

could be the source of the elevated ground level ozone, assuming the possibility or 

likelihood of sufficient downward mixing. As such, an experiment was designed to 

measure the local wintertime vertical ozone profile. If elevated concentrations were 

observed above the ground level or the inversion heights, the upper level ozone may be 

the source for the unexpectedly high concentrations recorded at the Logan station. 

METHODOLOGY 

In order to measure the vertical ozone concentrations a small airplane was 

outfitted with an ozone monitor, a temperature monitor, a GPS system, and two flights 

were conducted. The first flight was in the mid-afternoon of February 9, 2006 (13:41-

15:32). The second flight was in the early morning, just after sunrise, on February 11, 

2006 (7:02-8:59). A four meter Teflon tube with an outer diameter of 1⁄4” was attached to 
70

the wing strut of a Cessna 182 airplane. The tube ran to the inside of the plane and was 

attached to a ThermoEnvironmental Model 49C UV Photometric O3 Analyzer. Before 

the initial flight, the ozone monitor was calibrated using a ThermoEnvironmental Model 

49C Primary Standard O3 Calibrator. The data were averaged over one minute intervals 

and corrected for system sampling and instrument response time lags (approximately one 

minute). A HOBO temperature sensor was attached to the opposite strut and 

programmed for 15 second averaging periods. A Garmin Etrex Vista handheld GPS was 

used to track aircraft position and altitude. The flights were on a north-south transect 

along the length of the valley at above sea level elevations of around 1460 m, 1600 m, 

1950 m, and 2770 m, or above the valley floor elevations of approximately 90 m, 300 m, 

600 m, 1400 m. A sample flight path (February 9) can be seen in Figure 59. The flight 

path for the second profile (February 11) was similar. 

Flight Path (2/9/06)

1300

1500

1700

1900

2100

2300

2500

2700

2900

3100

4590 4600 4610 4620 4630 4640 4650 4660 4670

UTM(N); km

Elevation (m asl)

Figure 59. Flight path for February 9, 2006. 

RESULTS 

During the first flight ground level ozone concnetrations measured just before 

takeoff and after landing, were found to average approximately 35 ppb. At the UDAQ 

Logan station, approximately 5.6 km from the airport location, during the same time 

period ground level ozone was measured to be approximately 34-48 ppb (UDAQ, 2006). 

The ozone concentrations along the flight path are shown in Figure 59. The different 

elevation transects above the valley floor are shown in different colors (see legend on 

Figure 59). For most of the elevations flown, ozone concentrations were moderately 

consistent varying between 40-50 ppb. However, at the lower two transects, 90 m and 

300 m above ground level, the ozone concentrations displayed a noticeable decrease 

when flying over the mid-to-south end of the valley, the most densely populated area of 

the valley. Additionally, it should be noted that there was a 1.4 – 1.9 m/s wind blowing 

out of the Northwest. The investigators theorize that the reason the “Logan Dip,” as it 

was referred to, was not seen at the third and fourth transects (600 m – 1400 m) is 

because these final two transects were above the inversion height. Figure 60 shows a 
71

photograph taken from an elevation of approximately 1900 m (asl) clearly showing the 

inversion layer. 

Ozone Concentrations Along the Flight Path (2/9/06)

25

30

35

40

45

50

55

60

4590 4600 4610 4620 4630 4640 4650 4660 4670

UTM(N); km

Ozone (ppb)

90 meters 300 meters 600 meters 1400 meters 

Figure 59. Ozone concentrations along February 9, 2006 flight path (elevation transects 

are above ground level). 

Figure 60. Photograph of inversion above Cache Valley, Utah taken 2/9/06 at 1900 m 

(asl). 

The valley-wide average vertical ozone profile from the same day is shown in 

Figure 61. The ozone concentrations were low at ground level and rose to values 

approaching 50 ppb, then began to decrease at above sea level elevations of around 2000 

m. The 95% confidence intervals have a higher degree of variability at lower elevations. 

This coincides with the variability owing to the “Logan Dip” seen in Figure 59. 
72

However, above the inversion layer the 95% confidence intervals are small because the 

ozone was essentially the same horizontally (north-to-south) through the measured 

troposphere. 

Cache Valley Vertical Ozone Profile-Flight 2/9/06

1300

1500

1700

1900

2100

2300

2500

2700

2900

3100

10 20 30 40 50 60 70

Ozone (ppb) and Temp (F)

Elevation (m asl)

Temperature Ozone Avg O3 Avg Temp

Figure 61. Vertical temperature and ozone profile February 9 flight (error bars represent 

the 95% confidence interval). 

 Also shown in Figure 61 is the vertical temperature profile for the February 9th

flight. As described by Cooper and Alley (2002), an inversion is when temperature 

increases with altitude as opposed to the typical case of temperature decreasing vertically. 

A very pronounced inversion can be seen clearly delineated at approximately 650 m 

above ground level (2000 m asl). Most of the locally emitted reactive pollutants remain 

trapped under the inversion layer and are more concentrated at the south end of the valley 

due to population density and wind direction. This is also evidenced by the “Logan Dip” 

in Figure 59. 

The second flight in the early morning of February 11, 2006 found that ground 

level ozone was between 16-31 ppb. UDAQ reported that on that morning the Logan 

station ground level ozone was measured to be approximately 19-33 ppb (UDAQ, 2006). 

The ozone concentrations along the flight path are shown in Figure 62. As with the 

previous flight (Figure 59) the different elevation transects above the valley floor are 

shown in different colors (Figure 62). On the morning of the 11th, ozone concentrations 

were more consistent in regards to north-south variability and generally increased with 

elevation. 
73

Ozone Concentratons Along the Flight Path (2/11/06)

10

20

30

40

50

60

70

4590.000 4600.000 4610.000 4620.000 4630.000 4640.000 4650.000 4660.000 4670.000

UTM(N); km

Ozone (ppb)

90 meters 400 meters 600 meters 1400 meters 

Figure 62. Ozone concentrations along February 11, 2006 flight path (elevation transects 

are above ground level). 

Figure 63 shows the vertical temperature and ozone profiles for the February 11th flight. 

As elevation increased, there was a gradual increase in ozone up to approximately the 

same background concentration as observed on the February 9th afternoon flight. Once 

again the observed ground level ozone showed the highest degree of variability, which is 

likely due to different concentrations observed between the start (take-off) and ending 

(landing) of the flight period. 

Cache Valley Vertical Ozone Profile-Flight 2/11/06 

1300

1500

1700

1900

2100

2300

2500

2700

2900

0 10 20 30 40 50 60 70

Ozone (ppb) and Temp (F)

Elevation (m asl)

Temperature Ozone Avg O3 Avg Temp

Figure 63. Vertical temperature and ozone profile February 9 flight. 

This flight started before sunrise, at which point ground level ozone had had 

sufficient time overnight to titrate out by reacting with hydrocarbons and oxides of 

nitrogen. Upon landing the sun had risen and ozone formation chemistry had already 
74

begun (more insolation). The temperature profile (Figure 63) showed that there was a 

moderate, continuous inversion from ground level to the highest elevation. 

CONCLUSIONS 

Upon analysis of the data it was concluded that the wintertime high levels of 

ozone in Utah’s Cache Valley could indeed be a result of downward mixing from ozone 

aloft. The upper-level available ozone is likely being utilized at ground level, as well as 

produced, through the previously mentioned photochemical reactions to form particulatephase ammonium nitrate. 

Figure 64 directly compares the ozone concentrations from both flights. The 

ground level ozone was low in the morning hours compared to the afternoon flight due to 

reactions previously discussed. 

Ozone Cocentrations

1000

1500

2000

2500

3000

0 10 20 30 40 50 60 70

Ozone (ppb)

Elevation (m asl)

Feb 9 Afternoon Feb 11 Morning Ave O3 2/9/06 Ave O3 2/11/06

Figure 64. Ozone Concentration-both flights.

In the afternoon, a very pronounced dip in ozone concentrations over Logan served as 

evidence that the ozone is reacting with pollutants within the inversion boundary. The 

ozone concentrations were similar (45-55 ppb) above the inversion and generally 

increased with elevation. Although this study gives strong indication that free 

tropospheric ozone may supply sufficient concentrations to initiate photochemical 

reactions in Northern Utah’s Cache Valley, it is recommended that additional vertical 

ozone profiles be measured to determine if these results are typical throughout the winter 

period. Airplane transects are expensive and time consuming. It is suggested that other 

methods, such as radio sondes or tether sondes, be used for further analysis. 
75
76

Cache Valley Major Carbonyls (Winter 2005)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

"Bad" Air Averages

Formal (A) Formal (L) Acetal (A) Acetal(L) Aceton (A) Aceton (L)

 VOCs

Cache Valley Major Carbonyls (Winter 2005)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

"Good" Air Averages

Ambient (ppb)

Formal (A) Formal (L) Acetal (A) Acetal(L) Aceton (A) Aceton (L)
77

1 10 100 1000 10000

Gas-Phase NH3 (ppb)

Grocery Store

General Store

Restaurant

USU CEE Dept

Grade School

BRHD (gov)

Beutler Home

Martin Home

Dupont Home

KDM Apt

JTP Home

NEW RESEARCH 

Indoor NH3, 

Valley-wide NH3 

Jan. 20-25, 2006 

415000.00 425000.00

UTM (NAD27); m

4610000

4615000

4620000

4625000

4630000

4635000

4640000

4645000

4650000

4655000

4660000

UTM (NAD27); m

Logan

Franklin, ID

Preston, ID

Mendon

Cronish, UT

Newton

Smithfield

Wellsville

Trenton

Cutler

Reservoir
78

REFERENCES 

40CFR50, Title 40 Code of Federal Regulations, Part 50, Appendix L (2003), Reference 

Method for Determination of Fine Particulate Matter as PM2.5 in the Atmosphere, 

www.access.gpo.gov/nara/cfr/waisidx_03/40cfrv2_03.html, accessed December 2003. 

40CFR50, App. F (2006), Title 40 Code of Federal Regulations Part 50, National Primary 

and Secondary Ambient Air Quality Standards, Appendix F, Measurement Principle and 

Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere, 

accessed at washingtonwatchdog.org/documents/cfr/title40/part50.html. 

AirMetrics (2004), MiniVol Portable Air Sampler Operators Manual, 

www.airmetrics.com/products/minivol/index.html, accessed January 2004. 

Ansari A.S.and S.N. Pandis (1999), Prediction of multicomponent inorganic atmospheric 

aerosol behavior, Atmos. Environ., 33:745-757 

Arya, S. Pal (1999), Air Pollution Meteorology and Dispersion, Oxford University Press, 

Inc.: New York City, NY. 310. 

Blanchard, C.L., P.M. Roth, S.J. Tanenbaum, S.D. Ziman, and J.H. Seinfeld (2000), The 

Use of ambient measurement to identify which precursor species limit aerosol nitrate 

formation, J. Air Waste Manage. Assoc., 50:2073-2084. 

Cache County (2004), Utah, Assessor’s Office, Motor Vehicle Registration, personal 

communication. 

CAEAAFO (2002), The Scientific Basis for Estimating Emissions from Animal Feeding 

Operations, Interim Report, Committee on Air Emissions from Animal Feeding 

Operations, Division of Earth and Life Sciences, National Research Council, National 

Academy Press. 

CENR (2001), Atmospheric Ammonia: Sources and Fate, A Review of Ongoing Federal 

Research and Future Needs, Committee on the Environment and Natural Resources, air 

Quality Research Subcommittee, NOAA Aeronomy Laboratory, Boulder, CO, June 2000. 

Cooper, D.C. and F.C. Alley (2002), Air Pollution Control: A Design Approach, 

Waveland Press, Inc., Prospect Heights, Ill., U.S. 

Cowen, K., A.L. Sumner, A. Dindal, K. Riggs, Z. Willenberg, J. Hatfield, R. Pfieffer, and 

K. Scoggin (2004), Thermo Electron Corporation Model 17C Ammonia Analyzer, 

Environmental Technology Verification Report, ETV Advanced Monitoring Systems 

Center, Battelle, Columbus, OH, July 2004. 
79

El-Abssawy, A.A. (2003), Indoor-outdoor relationship of suspended particulate matter 

and its chemical composition at different sizes, Intern.l J. of Environ. and Pollut., 19: 

615-634. 

EPA (2003), Air Trends: Particulate Matter, www.epa.gov/airtrends/pm.html, accessed 

Feb. 2003. 

FAO (2001), Global Estimates of Gaseous Emissions of NH3, NO, and N20 from 

Agricultural Land, International Fertilizer Industry Association, Food and Agricultural 

Organization of the United Nations, Rome, 2001, ISBN 92-5-104698-1. 

Finlyason-Pitts, B.J. and J.N. Pitts, Jr. (2000), Chemistry of the Upper and Lower 

Atmosphere: Theory, Experiments, and Applications, Academic Press, San Diego, CA, 

pp 583. 

IDT, Idaho Transportation Department (2006), Idaho Vehicle Count and Registration 

Revenue: Calendar Year 2004, itd.idaho.gov/econ/VehicleRegistration/REG04.htm

(accessed Jan. 2006). 

Klausmeier, R and P. McClintock (2003), Virginia Remote Sensing Device Study - Final 

Report, ESP, Tucson, AZ. 

Lefohn A.S., Oltmans S.J. , Dann T. , and Singh H.B. (2001), Present-day variability of 

background ozone in the lower troposphere. J. Geophys. Res., 106 (D9):9945-9958. 

Mangelson, N.F., L. Lewis, J.M. Joseph, W. Cui, J. Machir, D.J. Eatough, L.B. Rees, T. 

Wilkerson, and D.T. Jensen, (1997), The contribution of sulfate and nitrate to 

atmospheric fine particles during winter inversion fogs in Cache Valley, Utah. J. Air 

Waste Manag. Assoc., 47:167-175. 

Martin, R.S. and D. Zhu (2004), Gas- and Particulate-Phase Ammonia in Northern Utah’s 

Cache Valley, No.72, presented at the Joint Regional Meeting of the Northwest and 

Rocky Mountain Sections of the American Chemical Society, Logan, UT, June 6-9, 

2004. 

Masters, Gilbert M. (1998), Introduction to Environmental Engineering and Science, 

Second Edition, Prentice-Hall, Inc.: Upper Saddle River, NJ: 651. 

McCulloch, R.B., G.S. Few, G.C. Murray, and V.P. Aneja, (1998), Analysis of ammonia, 

ammonium aerosols, and acid gases in the atmosphere at a commercial hog farm in 

eastern North Carolina, USA, Environ. Pollut., 102:263-268. 

Mount, G.H., B. Rumburg, J. Havig, B. Lamb, H. Westberg, D. Yonge, K. Johnson, and 

R. Kincaid (2002.), The measurement of atmospheric ammonia at a dairy using 

differential optical absorption spectroscopy in the mid-ultraviolet, Atmos. Environ. 

36:1799-1810. 
80

Pryor, S.C., R.J. Barthelmie, L.L. Sorensen, and B. Jenson (2001), Ammonia 

concentrations and fluxes over a forest in the midwest USA, Atmos. Environ., 35:5645-

5656. 

Robarge, W., J. Walker, G. Murray, and W. Cure (2000), Ambient Concentrations of 

Ammonia in Eastern North Carolina, presented at the EPA Great Waters Program 

Workshop: Airsheds and Watersheds: The Significance of Ammonia to Coastal & 

Estuarine Areas, Nov. 15-16, 2000, Dewey Beach, Delaware. 

Sawant, A.A., K. Na, X. Zhu, K. Cocker, S. Butt, C. Song, D.R. Cocker III (2004), 

Characterization of PM2.5 and selected compounds at multiple indoor and outdoor sites in 

Mira Loma, California, Atmos. Environ., 38: 6269-6278. 

Seinfeld, J.H. and S.N. Pandis (1998), Atmospheric Chemistry and Physics: From Air

Pollution to Climate Change, John Wiley & Sons, Inc. New York, New York, 1326. 

Sonoran Insitute (2006), Population, Employment, Earnings, and Personal Income 

Trends: Franklin County, Idaho, Sonoran Institute, Bozeman, MT, 

www.sonoran.org/programs/data/IDFranklin.pdf (accessed Jan. 2006). 

TECO (2004), ThermoEnvironmental Instruments, Model 17C Chemiluminescent 

Ammonia Analyzer, Operations Manual. 

TECO (2006), ThermoEnvironmental Instruments, website, 

thermo.com/com/CDA/Category/All_Sub_Child_Category/0,2211,15,00.html, accessed 

April 2006. 

Thoni, L., E. Seitler, A. Blatter, and A. Neftel (2003), A passive sampling method to 

determine ammonia in ambient air, J. Environ. Monit., 5(1), 96-99. 

UGOPB (2006), Utah’s 2006 Economic Report to the Governor, Governor’s Office of 

Planning and Budget, www.governor.state.ut.us/dea/ERG/ERG2003/ERG2003.pdf 

(accessed Jan. 2006). 

URG (2000), Model 3000C/3000CA Operation Manual, URG, Chapel Hill, NC. 

Utah Division of Air Quality (2006), personal communication. 

Watson, J.G., J.C. Chow, F.W. Lurmann, and S.P. Musarra (1994), Ammonium nitrate, 

nitrate acid, and ammonium equilibrium in wintertime Phoenix, Arizona, J. Air Waste 

Manag, Assoc., 44:405-412. 

Whiteman, C. D., J. M. Hubbe, and W. J. Shaw (2000), Evaluation of an inexpensive 

temperature datalogger for meteorological applications, Journal of Atmospheric and 

Oceanic Technology. 17: 77-81. 
81

Woods Hole Oceanographic Institution (2006), Ozone Measurements in the Marine 

Boundary Layer from Ocean Buoys, 

http://www.whoi.edu/MCG/facilities/hintsa_ozone/background.html, accessed May 2006. 

Yoong, M. (1981), Measurement of ambient ammonia concentrations in Southern 

California, Final Report, prepared for the California Air Resources Board, Contract A7-

188-30, Rockwell Internationl, Newberry Park, CA. 

Zhu, Dongzi (2005), Analysis of Wintertime Gas- and Particulate-Phase Ammonia in 

Assocation with PM2.5 Formation in Cache Valley, M.S. Thesis, Utah State University, 

Logan, UT, June 2005.