DAQ-2024-011368

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Quantification of Halogen-Initiated Atmospheric Chemistry in the Wasatch Front

Applicant Information:
Principal Investigator: Dr. Demetrios Pagonis
Weber State University
Department of Chemistry and Biochemistry
Ogden, UT 84408
[e-mail]
801-626-6086

Weber State University Sponsored Projects Office:
Brooke Lindgren
3850 Dixon Parkway
Department 1027, Room 102
Ogden, UT 84408
[e-mail]
801-626-7629

Funding Requested:
From UDAQ: $30,955

Project Period:
July 1, 2024 – June 30, 2025

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Abstract
The atmospheric chemistry of the Salt Lake City airshed is distinct from other metropolitan areas
in the United States due to the region’s unique combination of industrial halogen emissions and
topography. Over 50% of the chlorine emissions in the United States occur within 50 miles of
downtown Salt Lake City.1 Efforts to model the impacts of these emissions have predicted
significant impacts on the region’s oxidation budget, ozone concentrations, and particulate matter
(PM) concentrations.2 However, these model predictions have lacked support from measurements
of halogen-initiated chemistry in the area. This study aims to quantify the extent of halogen-
initiated oxidation of volatile organic compounds in the Salt Lake City airshed. This will be
accomplished through quantitative offline GC-MS measurement of chloroacetone and alkyl
nitrates. Chloroacetone is a product of chlorine-initiated VOC oxidation. The isomer ratios of alkyl
nitrates provide further insight into which atmospheric oxidant (OH radical or Cl radical) initiated
most of the oxidation in an airmass. This project will provide UDAQ with direct measurements of
the extent to which regional halogen emissions are initiating the chemistry responsible for regional
ozone and PM.
Basis and Rationale
Ozone is a regulated pollutant, and the Northern Wasatch Front frequently exceeds the EPA
NAAQS limits. In order for UDAQ to effectively address the region’s air pollution, a detailed
understanding of the chemical processes responsible for ozone production is required.
Accordingly, “summertime ozone chemistry and sources” is one of the goals and priorities for this
funding cycle of Science for Solutions research grants.
When Utah is impacted by summertime ozone, how much of the photochemical ozone production
is initiated by halogens?
Much of our current
understanding of the extent to which
halogen emissions in Utah impact
ozone production is limited to a
single modeling study.2 This study
constrained halogen emissions
through line-of-sight measurements
of plumes from the US Magnesium
facility in Rowley, UT. These
emission rates were then added to a
chemical transport model (CAM-
chem), which predicted that the
halogen emissions were responsible
for significant (10-25%) increases in
PM and ozone concentration in the
Northern Wasatch Front (Figure 1).
These model results indicate that
halogen-initiated chemistry has the
potential to significantly impact
regional ozone and PM
Figure 1. Adapted from Womack et al. 2023. CAM-chem model
results showing the enhancement in surface ozone and particulate
matter concentrations in urban areas when halogen emissions from
US Magnesium are included in the model.
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concentrations, but there is a lack of measurements in support of this model prediction. This is
largely because halogen chemistry is complex, rapid, and non-linear.3-6
Chlorine (Cl2) and bromine (Br2) emissions photolyze rapidly during the day (τ = 6 minutes
and 0.5 minutes, respectively),7 and so one can only measure Cl2 and Br2 close to an emission
source, or at night. However, the impacts of chlorine chemistry predicted by modeling2 are
widespread. This is because the radicals produced from Cl2 photolysis go on to initiate many
generations of atmospheric oxidation through the reactions of Cl˙, ClO, ClNO2, and particle-phase
chloride. Therefore, even if one did measure all the forms of chlorine in an airmass, one would
not know how much oxidation that chlorine had initiated. Without quantifying the extent of
chlorine-initiated chemistry, one cannot validate model predictions of the impact chlorine has on
regional ozone and PM concentrations.
Therefore, the best approach to determining the impact of chlorine on regional chemistry is to
measure the products of chlorine-initiated VOC chemistry, rather than measure the chlorine itself.
This proposal leverages known oxidation mechanisms of VOCs8-10 to identify the chemical
signature of chlorine- and bromine-initiated oxidation in the Wasatch Front. The proposed
approach relies on two methods to accomplish this goal. The first is quantification of chloroacetone
and bromoacetone, first-generation oxidation products of halogen radicals with propene. The
second method quantifies the ratio of halogen-initiated VOC chemistry to OH-initiated chemistry
based on the higher yield of primary alkyl nitrates from reactions of Cl˙ with alkanes.
The target molecules chloroacetone and bromoacetone are produced in the atmosphere by the
chemical mechanism shown in Figure 2. The halogen radical adds to the double bond, and in the
presence of NOx the peroxy radical rapidly reacts to give a ketone. This approach has previously
been used to constrain the extent of Cl-initiated chemistry in the Houston airshed11,12 and the
arctic.10,13 The strength of chloroacetone as an indicator of Cl-initiated chemistry is that the
halogen is retained in the product molecule. Thus, it is a molecule that is highly specific to halogen-
initiated chemistry. However, the production rate of chloroacetone is dependent on the presence
of propene, a reactive alkene that is not expected to be present in regional background air. Thus,
chloroacetone and bromoacetone are likely to be indicators of halogen chemistry that occurs after
Figure 2. The chemical scheme for chloroacetone formation from propene. An identical mechanism follows if
bromine adds to the double bond, giving bromoacetone as a product. Analogous chemistry occurs with other
alkenes, forming chloro- and bromo- ketones and aldehydes.
Figure 3. The mechanism for formation of an alkyl nitrate from the oxidation of propane. The initial hydrogen
abstraction can be done by OH or Cl radicals, and the subsequent chemistry is identical. In the mechanism
shown, the initial hydrogen abstraction occurs in the middle of the carbon chain, producing isopropyl nitrate.
If the reaction were initiated at the end of the carbon chain instead, the product would be n-propyl nitrate,
shown in Figure 4 below.
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halogens have mixed with fresher emissions from within the Salt Lake City airshed. Because of
this potential weakness in the method, we plan to also measure alkyl nitrates as detailed below.
We also propose to measure the ratios of n-propyl nitrate to isopropyl nitrate, and n-butyl
nitrate to isobutyl nitrate. These alkyl nitrates are products of propane and butane oxidation (Figure
3), and the ratio of the isomers produced depends on whether the parent alkane (propane or
butane) reacted with Cl˙ or OH˙ (Figure 4). When OH radicals react with an alkane, it is much
more favorable to abstract from a secondary carbon (-CH2-, middle of the carbon chain), and so
one produces higher yields of secondary alkyl nitrates.9 However, Cl˙ is much more capable of
reacting at a primary (-CH3, end of the chain) carbon, and so the yield of the primary alkyl nitrate
(n-propyl nitrate) is more than twice that of the secondary nitrate (isopropyl nitrate).14 These alkyl
nitrate products photolyze slowly (τ > 10 days),7 and are significantly less reactive towards OH
and Cl than the parent alkanes.14 These properties make them sufficiently long-lived and
unreactive to allow them to be used as reliable tracers of Cl-initiated chemistry.
The strength of this approach is that one expects meaningful background concentrations of
propane and butane in any airmass that also contains halogens. This enables us to quantify the ratio
of OH radical to Cl radical exposure in the airmass. In air that has seen significant Cl-initiated
oxidation, we expect to observe elevated ratios of primary:secondary alkyl nitrates. Secondly, the
yields shown above are independent of NOx concentrations in the airmass, since any reaction
pathway not involving NO will not produce an alkyl nitrate. Therefore, even if the chemistry of a
particular airmass is transitional (instead of high-NOx), the proposed analysis is still representative
of Cl radical exposure.
The most likely pitfall to be encountered in this approach is the low concentrations of the alkyl
nitrate products in some airmasses. This can be counteracted through longer sampling times and
modification of the GC-MS duty cycle. We will modify our methods as needed to bring detection
limits down. Analysis of past Tenax sorbent tube samples from the Salt Lake City airshed showed
evidence of alkyl nitrates in samples lasting one hour and without using an optimized GC-MS duty
cycle. Therefore, we are confident that the increased sampling times and improved duty cycle
proposed below will lead to sufficiently low detection limits to carry out the proposed analysis.
Technical Approach
Quantification of target VOC concentrations
The concentrations of alkyl nitrates, chloroacetone, and bromoacetone in the Salt Lake City
airshed will be determined through sorbent tube sampling and gas-chromatography mass
spectrometry (GC-MS). A combination of Carboxen and Tenax TA sorbents will be used to ensure
high sorption efficiency across the relevant volatility range.
Figure 4. Relative yields of isopropyl and n-propyl nitrates from the oxidation of propane by OH and Cl radicals.
The yield of and n-propyl nitrate is significantly higher for chlorine-initiated oxidation, allowing one to use alkyl
nitrate isomer ratios to calculate relative amounts of OH-initiated and Cl-initiated oxidation. Similar trends occur
in the formation of isobutyl and n-butyl nitrates, which will also be quantified by this study.
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This approach follows the methodology of past studies that quantified Cl˙ and Br˙
concentrations in Houston and the arctic.8,11-13 This method is expected to achieve detection limits
in the part per trillion range for all target VOCs. This will be accomplished through a combination
of long sample collection times (2-24 hr) and selected ion monitoring in the GC-MS method. The
longer sampling times will collect greater quantities of chloroacetone and bromoacetone on the
sorbent tubes, and selected ion monitoring will increase the efficiency with which the characteristic
ions of these compounds are detected.
The GC-MS signals of all target compounds will be quantified using standards. Chloroacetone
is commercially available and inexpensive ($0.41 per gram). Bromoacetone is readily synthesized
from aqueous bromine and acetone. This technique is so straightforward that it has historically
been used as a classroom demonstration.15 Reaction yields are high and will be quantified using
nuclear magnetic resonance spectroscopy (NMR). Weber State University’s 90 MHz Anasazi
NMR is capable of making this measurement. Alkyl nitrates will be synthesized from primary and
secondary alcohols.16 Preliminary synthesis at Weber State have been successful.
Field sampling alongside Utah Summer Oxidant Study
Sorbent tube sampling will be conducted throughout the duration of the 2024 Utah Summer
Oxidant Study (USOS), July 14th-August 12th. We intend to carry out continuous fixed-point
sampling at the Rose Park field site, taking two samples each day. Overnight samples will be
collected from 9:00 PM until 6:00 AM, and daylight samples will run from 6:00 AM until 9:00
PM each day. A solenoid valve system and microcontroller will allow for unattended sample
switching. Samples will be retrieved daily and returned to Weber State for analysis.
We plan to supplement this continuous record with intermittent samples at additional sites.
These will be chosen responsively throughout USOS based on the flight and drive plans of the
NOAA Twin Otter and NOAA mobile laboratory. On days without planned research flights or
drives, candidate sites for intermittent sampling include Viewmont High School, Antelope Island,
Lee Creek Natural Area, Stansbury Island, and Timpie Springs Waterfowl Management Area
(Figure X). These sites are publicly accessible and cover much of the Northern Wasatch Front
ozone nonattainment area, including the areas near Rowley, UT which Governor Cox has
requested to add to the non-attainment area.17 All sampling equipment to be used at these sites is
portable, battery-powered, and leaves no impact on the sampling site.
Supplemental Winter Measurements
In the winter of 2024-2025 we will return to Rose Park for additional intermittent sampling
during periods of increased PM pollution, to assess the impact of halogen chemistry on winter air
quality. These measurements are responsive to the RFP under the topic of Meteorology-Chemistry
Coupling, which calls for investigations of chemical mechanisms that impact winter air quality.
Similar to the intermittent summer sampling, these winter measurements can be supported by
battery power and do not require infrastructure support from UDAQ.
Parameter Measurement
Chloroacetone, bromoacetone,
C3 and C4 alkyl nitrates
Carboxen sorbent tube,
offline GC-MS
Ozone 2B Tech 205 Ozone Monitor
Meteorological conditions Wind speed, direction,
pressure, temperature
Table 1. Proposed measurements for intermittent sampling sites.
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Expected Outcomes and Outputs
The outputs of this study are measurements of the extent of chlorine and bromine-initiated
chemistry in the Salt Lake City airshed. The integrated estimates of Cl˙ and Br˙ exposure during
USOS and winter 2024-2025 can be used to evaluate CAMx model output in UDAQ’s future
efforts modeling air quality in the region. The carbon bond 6 mechanism (cb6r5h) utilized by
UDAQ in CAMx tracks alkyl nitrate production, halogen radicals, OH radicals, and select VOCs.
These model parameters can be directly related to the outputs of this study, which quantify the
extent to which OH and Cl are initiating VOC oxidation. The inclusion of halogens in the carbon
bond 6 mechanism by Ramboll is not yet publicly available, and future revisions of this mechanism
are likely. This work provides the molecular measurements that are essential for constraining and
validating UDAQ’s future mechanism development. The combined approach of continuous
measurement at a single site (Rose Park) and intermittent sampling in other areas (Figure 5)
ensures that the outputs of this study help DAQ constrain both the spatial and temporal variability
in the impacts of halogen emissions on air quality in the region.
Deliverables
The deliverables of this study to DAQ are summarized in the table below. All data will be
summarized in quarterly and final reports, and will also be provided to UDAQ directly.

Data Product Location(s) Timeframe(s)
Chloroacetone concentration (ppt)
Rose Park and
intermittent sampling
sites (Fig. 5)
Continuous measurements July 14th-
August 12th (Rose Park)
Bromoacetone concentration (ppt)
n-propyl nitrate concentration (ppt)
Isopropyl nitrate concentration (ppt)
n-butyl nitrate concentration (ppt)
Figure 5. Proposed sites for intermittent sampling to supplement the continuous Rose Park data. These sites align
with HYSPLIT modeling of typical transport of US Magnesium emissions in the summertime previously used by
UDAQ. 17
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Isobutyl nitrate concentration (ppt) Intermittent sampling July 14th-
August 12th
Intermittent sampling Dec 2024-
February 2025 (Rose Park)
Cl exposure (molec cm-3 s)
OH exposure (molec cm-3 s)
OH:Cl exposure ratio
Ozone concentration (ppb) Intermittent sampling
sites (Fig. 5)
July 14th-August 12th
Intermittent sampling Dec 2024-
February 2025 (Rose Park)

Schedule
July
Aug
Sept
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
June
Field measurements, GC-MS analysis
Standard synthesis, GC-MS quantification
Results presented at 2025 Science for
Solutions conference

Final data and report to UDAQ

Field data for this project will be collected in two parts of the year. The first field intensive
aligns with the USOS study in July and August 2024. Additional measurements will be made
during PM2.5 air pollution episodes in winter 2024/2025. The months between these field
intensives will be dedicated to finalizing quantification of GC-MS data from the summer. Project
results will be presented at the 2025 Science for Solutions Air Quality conference and final data
and the final project report will be delivered to UDAQ by June 2025.
Budget

Task 1
Field Sampling and
GC-MS analysis
Task 2
Standard synthesis and
GC-MS quantification Total
PERSONNEL
Two Research Assistants at $20/hr for
500 hr $4,000 $6,000 $10,000
Dr. Pagonis at $8,162/mo for 1 month $3,265 $4,897 $8,162
FRINGE BENEFITS
at 8.5% (Student) $340 $510 $850
at 22% (Faculty) $719 $1077 $1,796
SUPPLIES
Reagents and standards $0 $2373 $2373
Carboxen sorbent and sorbent tubes $1,276 $0 $1,276
Sampling equipment $2175 $0 $2175
Consumables $100 $400 $500
TRAVEL $3,753 $0 $3,753
DATA MANAGEMENT $70 $0 $70
TOTAL DIRECT COSTS $15,698 $15,257 $30,955
TOTAL INDIRECT COSTS $0 $0 $0
TOTAL PROJECT COST $30,955
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Indirect costs
Weber State University agrees to waive its standard indirect cost rate of 35% for this project.
Supplies
Cost of chemical reagents and standards was determined based on January 2024 prices at
Millipore Sigma. These reagents allow for preparation of all standards needed to quantify the target
molecules listed above as deliverable to UDAQ. Cost is summarized in the table below.

Quantity Millipore Sigma SKU Cost
1-propanol 500 mL 402893-500ML $ 74.00
2-propanol 500 mL 190764-500ML $ 76.80
1-butanol 500 mL 360465-500ML $ 78.90
2-butanol 1 L B85919-1L $ 76.00
Chloroacetone 100 g 167479-100G $ 40.60
Acetone 500 mL 179124-500ML $ 68.20
Bromine 100 g 277576-100G $ 118.00
Nitric acid 100 mL 438073-100ML $ 55.70
Sulfuric acid 100 mL 258105-100ML $ 55.00
Solvents 12 L 439193-4L, 34851-4L,
34858-4L $ 1,035.00
Deuterated NMR solvent 50 g 175943-50G $ 220.00
Alkane standards 5 mL 04070-5ML $ 259.00
Estimated Shipping (10%) $ 220.00
Total $ 2,373

Carboxen sorbent ($655, SKU 10471) and a set of 25 sorbent tubes ($621, SKU 2046625) to
cover the sustained sampling during USOS is budgeted at $1276.

The cost of necessary sampling equipment is tabulated below. Prices of tubing and orifices are
based on January 2024 prices at McMaster Carr, and fitting costs are from January 2024 prices at
Swagelok. All other costs are based on January 2024 rates on Amazon, and include the discounted
rates negotiated by the University.

Quantity Cost
PFA tubing 100 feet $ 445.00
Critical orifices 20 $ 360.00
Fittings 50 fittings, average $16 each $ 800.00
Valves, pumps Manifolds for 7 sorbent tubes $ 250.00
Arduino microcontrollers 4 $ 80.00
12 V, 10 Ah lithium batteries 6 $ 240.00
Total $ 2,175.00

We also include $500 to cover the costs of consumables, including gloves, glassware, wire,
GC sample vials, syringes, and other supplies needed to complete the tasks above.
Travel needs
Travel to and from sampling sites is budgeted at Weber State’s standard mileage rate of $0.655
per mile. The budget assumes daily trips from Weber State to Rose Park (60 miles round trip) for
the duration of USOS. The budget also supports additional mileage for reaching the intermittent
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sampling sites on 15 summer days (up to 150 miles round trip) and travel to Rose Park for 10
winter days.

Mileage Cost
Daily USOS sampling, Rose Park 48 days × 60 miles = 2,880 miles $1,886
Intermittent sampling, summer 15 days × 150 miles = 2,250 miles $1,474
Intermittent sampling, winter 10 days × 60 miles = 600 miles $393
Total 5730 miles $3,753

Data management
The budget above includes $70 to support continuous, redundant backup of all data produced
by this project. All data will be backed up a minimum of three times, through a combination of
physical backups on-site at Weber State and cloud-based storage. The cost of cloud storage is
contributed in-kind by Weber State, and the $70 budget item covers the cost of hard drives for
backing up data. Final data will be provided to UDAQ in ICARTT format for public posting, and
the requirement for 10-year availability can be further supported by publicly archiving study data
through Zenodo.
Personnel Roles and Responsibilities
The Principal Investigator, Dr. Demetrios Pagonis, will be responsible for managing all aspects
of the project. He will purchase all necessary materials, assemble the sampling equipment, hire
and train two research students, participate in field sampling, assist in analyzing GC-MS data, and
provide technical guidance in the synthesis of standards. He will also be responsible for all
intermediate and final reports to UDAQ under this award.
Research Assistants: Two undergraduate research students, who will be hired in 2024, will be
responsible for collecting field samples at Rose Park and the intermittent sites, running sorbent
tubes on the GC-MS, and synthesizing & analyzing chemical standards. The timeline of award
notification included in the RFP (decisions released May 3, 2024) provides sufficient time for
research assistants to be fully hired and ready to begin on July 1, 2024.
Dr. Pagonis has previously deployed a wide variety of aerosol- and gas-phase instrumentation
in ground-based and airborne field settings. This includes two years of experience with sampling
air toxics and semi-volatile organic compounds using the same methodology as this project. He
has mentored numerous undergraduate researchers, training several to collect and analyze sorbent
tubes with the GC-MS to be used in this project. If funded, these students will be encouraged to
apply for the student positions above. Dr. Pagonis also has experience participating in and
analyzing data from multi-platform field studies. His most recent publication18 combines data from
eleven airborne, mobile lab, and ground studies of wildfire smoke. That study successfully
accounts for much of the discrepancy in wildfire smoke measurements between airborne
measurements and those at ground level. Thus, Dr. Pagonis has the necessary experience to
interpret the results of this study in the broader context of the USOS dataset.

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