Analysis of mobile source air toxics (MSATs)–Near-road VOC and carbonyl
concentrations
Sue Kimbrough*
U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management
Research Laboratory, 109 TW Alexander Dr., RTP, NC 27711
Ted Palma,
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, 109 TW Alexander Dr.,
RTP, NC 27711
Richard W. Baldauf,
U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management
Research Laboratory, 109 TW Alexander Dr., RTP, NC 27711
U.S. Environmental Protection Agency, Office of Transportation and Air Quality, 2000 Traverwood Dr.., Ann
Arbor, MI 48105
Supplemental Information
Analytical Methods and Instruments
Table S1 provides a summary of the instrumentation and measurements discussed herein. MSAT
samples were collected using U.S. EPA standard methods: (1) TO-15 and (2) TO-11A (U.S. EPA,
1999a; U.S. EPA, 1999b). Nine 1-hour integrated samples were collected on a 1-in-12 day ambient air
quality monitoring schedule (U.S. EPA, 2010). Acrolein analysis was conducted using both the U.S.
EPA TO-11A and U.S. EPA TO-15 methods.
Table S1. Summary of measurements discussed herein (Kimbrough et al., 2013).
Distance from I-15 (m)
Instrument Data
Upwind
Measurement
Parameter
Downwind
100
20
100
300
Sampling
Approach
Make/Model
Accuracy
Precision
Detection
Limit
Sample Type
and
Frequency
Thermo Scientific TEOM –
1405-DF FDMS
±0.75%
±2.0 μg/m³ (1-hour
ave), ±1.0 μg/m³
(24-hour ave)
0.1 μg/m³
Continuous
(5 minute)
FEM TEOM
Gravimetric
(oscillating
microbalance)
PM2.5 FRM
Method (filter)
FRM BGI PQ200
EPA FRM Reference Method
X
Optical – light
attenuation
Magee Scientific –
Aethalometer (AE 21)
X
sonic
anemometer
RM Young Model 81000
PM2.5, PM10,
PMCoarse Mass
X
a
X
X
X
PM2.5 Mass
X
X
X
X
Black Carbon
X
X
X
X
X
X
Wind Speed
Wind Direction
1:1 comparison
w/ EC on filters
±0.05 m/s
± 5°
Repeatability: 1 part
in 10,000
std. dev. 0.05 m/s at
12 m/s
0.1 μg/m3 w
1 min res.
Continuous
(5 minute)
0.01 m/s
± 10°
0.1°
Continuous
(5 minute)
---
Met tower height above ground level (m) -- includes shelter height: 11.8
Traffic (vehicle
counts, speed)
a
Not applicable
Data provided by Nevada DOT
radar
1-in12 day
24-hour
Not applicable
Radar (Wavetronix)
Co-located BGI PQ200 Sampler
FEM = Federal Equivalent Method; TEOM = Tapered element microbalance; FRM = Federal Reference Method.
Continuous
(15 minutes)
U.S. EPA Compendium Method TO-15 – Canisters – VOC. Collection of canister samples by the TO15 method (benzene, 1,3-butadiene) calls for the atmosphere to be sampled by the introduction of air
into a specially-prepared stainless steel canister. An Entech Model 1816 programmable multi-canister
automated sampler [Entech Instruments, Inc., Simi Valley, California (CA)] was used to regulate the
filling of the sample canisters. Evacuated SUMMA passivated 6 liter (L) canisters were filled to at a
nominal flow rate of 75 milliliter/minute (mL/min) to maintain a 1-hour sampling period for a total
sampled volume of approximately 4.5 L. Evacuated canisters received from the laboratory and ready
for sampling using TO-15 cleaning protocols were placed on the Entech sampling system by attaching
each canister’s valve to individual sampling ports. The initial pressure was measured for each canister
to insure that every canister falls within an acceptable pressure range (<0.5 psia). Any canisters above
the acceptable range were replaced with one that met the initial pressure criteria. With the canisters
attached, each port was leak checked to insure that fittings had been properly tightened. Sample labels
printed with the individual sample codes were affixed to the canister tags for sample identification.
The sampler was programmed for the scheduled sampling times and flow rates. Timers and solenoids
within the Entech sampler were activated and deactivated allowing sample collection based on the
entered sampling program. After the air samples were collected, the canister valves were closed and
the canisters prepared for shipment to the laboratory for analysis. Sample collection information such
as initial and final pressures, initial and final times, canister id number, etc. were either hand recorded
on a data collection form for subsequent entry in the electronic data form or entered directly into the
electronic data form. Chain-of-custody (COC) sheets were generated and the samples were shipped to
the laboratory for analysis using TO-15 methods. Upon receipt at the laboratory, the canister sample
label was compared against the datasheet and the COC sheet. Any discrepancies were resolved at that
time. Table S2 shows a summary of canister (TO-15) samples by type.
U.S. EPA Compendium Method TO-11A – Cartridges – Carbonyl. The U.S. EPA Compendium TO11A DNPH carbonyl method was implemented in Las Vegas for the collection and analysis of air
samples for acrolein, acetaldehyde and formaldehyde. DNPH sampling cartridges [Sigma-Aldrich, St.
Louis, Missouri (MO)] are commercially available for this method and were purchased and provided
for field sampling. Air samples for carbonyls on DNPH cartridges were collected using an ATEC 8010
automated sampler [Atmospheric Technology (Atec), Malibu, CA)]. The instrument is a
microprocessor controlled sampler that can be programmed to draw ambient air at a constant rate
through various types of sampling cartridges for designated time periods. The sampler consists of two
units (channels) each having 10 active sampling ports and one non-active port for the field blank.
DNPH samples were collected at a flow rate of 1.00 liters per minute (lpm) for a one hour time period.
Nine DNPH cartridges were attached to the ATEC’s Teflon sampling lines and labeled with the sample
collection code. A leak check of each cartridge was performed using the leak check feature of the Atec
sampler. This ensured that the cartridges were installed properly. A light blocking sleeve was installed
around each cartridge to reduce artifacts due to light sensitivity. The sampler was programmed with the
flow, start time and end time for each cartridge channel. During sampling, solenoid valves associated
with each cartridge were activated/deactivated based on the programmed sampling schedule. Upon
completion of sampling, the cartridges were removed, capped, secured for shipment, and returned via
overnight delivery to the U.S. EPA Research Triangle Park, North Carolina (NC) facility for analysis.
Sample collection information such as initial and final flow rates, initial and final times, canister id
number, etc. were either hand recorded on a data collection form for subsequent entry in the electronic
data form or entered directly into the electronic data form. COC sheets were generated and the samples
shipped to the laboratory. While awaiting shipping, samples were stored in an on-site refrigerator. A
cooler with frozen blue ice packs was used to ship the cartridges. Table S2 shows a summary of
carbonyl (TO-11a) samples by type. All laboratory procedures followed the procedures outlined in
TO-11A.
Table S2. Summary of canister (TO-15) and cartridge (TO-11A) samples collected.
Sample type
No. of
samples
% by
sample
type†
No. of total
samples with
no sample
collection
errors/
warnings
% of total
samples with no
sample collection
errors/warnings†
No. of total
samples with
sample collection
errors/
warnings
% of total
samples
with sample
collection
errors/
warnings†
TO-15–1,3-butadiene and benzene.
Field Blank
Field Control
Field Duplicate
Lab Duplicate
System Test
Sample
Total
69
69
69
108
44
1185
1544
4
4
4
7
3
77
55
56
52
89
--1019
1271
80
80
75
82
--86
14
13
17
19
--166
229
20
20
25
18
--14
TO-11A– acrolein, acetaldehyde, and formaldehyde.
Field Blank
67
5
53
4
14
21
Field Control
72
5
51
4
21
29
Field Duplicate
67
5
33
2
34
51
Lab Duplicate
2
0
0
0
2
100
System Test
20
1
--------Sample
1191
84
812
68
379
32
Total
1419
969
450
†Percentages shown are based on percent of total samples collected. Percentages may not total to 100% due to rounding.
Background Corrections, measurement and analytical issues. The study did not provide any usable
carbonyl data for Station 3 (300 m downwind site). The instrument at Station 3 experienced problems
throughout the duration of the study. Thus, all carbonyl data collected at Station 3 were considered
invalid. Background corrections were not performed on the formaldehyde data since the field blank
values were below the method detection limit. Background corrections were performed on the
acetaldehyde and acrolein data.
Properly stored DNPH cartridges may be used over several weeks or months. For this year-long study,
DNPH cartridges were purchased multiple times to ensure use within 3 months. Typically, field blanks
were drawn from the same batch as the sample cartridges, although there were cases when field blanks
were drawn from different batches than those used for sampling. Thus, there were two cases: 1) field
blanks drawn from the same batch as field samples; and 2) no field blanks drawn from the same batch
as field samples. For case 1, the median value by batch by pollutant of the reported field blank values
was used as the background correction. For case 2, an overall median value by pollutant for the entire
set of reported field blank values was used for the background correction. If corrected values were
calculated as negatives or below the method detection limit, then the corrected values were replaced
with the method detection limit value; otherwise the corrected value is the actual calculated value.
NO2 Interferences
The interference of NO2 in this context would be the suppression of the formation of a stable derivative
with the DNPH reagent. The implication of this would be less formaldehyde would be extracted and
measured by the laboratory analysis (HPLC). Several studies have investigated NO2 interferences
when utilizing the DNPH sampling method (Karst et al., 1993; Komazaki et al., 1998; Tang et al.,
2004). Karst et al. (1993) reported NO2 interferences, while Komazaki et al. (1998) and Tang et al.
(2004) did not report NO2 interferences.
Formaldehyde concentrations were compared with NO2 concentrations by hour of the day for
downwind conditions for Station 1 (Figure S1c). While there were times during the day (midnight - 6
am) when formaldehyde concentrations were low compared to NO2 concentrations, this may be due to
lower traffic volumes occurring at these hours of the day as opposed to NO2 interferences. Figure S1a,
S1b and S1c shows diurnal traffic volume, formaldehyde, and the formaldehyde/NO2 ratio. The
implication of a low formaldehyde-to-NO2 ratio relative to formaldehyde is that interferences from
NO2 do not appear to be present. Thus, based on the measurement data collected, no obvious
interferences from NO2 were observed.
Figure S1. (a) Diurnal traffic volume. (b) Formaldehyde, and formaldehyde/NO2 ratio. (c) Formaldehyde and
NO2. – Station 1. (Each error bar is constructed using 1 standard deviation from the mean.)
MSAT Emissions, Traffic Data and Vehicle Fleet Mix
Nationally, the estimated 2008 National Emissions Inventory (NEI) contribution of highway vehicle
emissions to 1,3-butadiene, benzene, acrolein acetaldehyde and formaldehyde to the total
anthropogenic emissions for each species is shown in Table S3. The highway vehicle contribution to
the national emissions total for 1,3-butadiene, benzene, acrolein, acetaldehyde and formaldehyde is
24%, 33%, 6%, 4%, and 4% respectively (U.S. EPA, 2008). The contribution to the national total
emissions from on-road gasoline vehicles for 1,3-butadiene, benzene, acrolein acetaldehyde and
formaldehyde is 23%, 32%, 3%, 3%, and 2%, respectively (U.S. EPA, 2008). The contribution to the
national total emissions from on-road diesel vehicles ranges from 1% to 3% for each of the relevant
species.
The 2008 National Emissions Inventory for Clark County, NV which includes the Las Vegas urban
area contribution of highway vehicle emissions of 1,3-butadiene, benzene, acrolein acetaldehyde and
formaldehyde to the total anthropogenic emissions for each species is 42%, 52%, 22%, 1%, and 2%
respectively (Supplemental Information, Table S3) (U.S. EPA, 2008). The contribution to the Clark
County total emissions from on-road gasoline vehicles for 1,3-butadiene, benzene, acrolein
acetaldehyde and formaldehyde is 40%, 52%, 13%, 1%, and 2%, respectively (U.S. EPA, 2008). The
contribution to the Clark County total emissions from on-road diesel for each of these species is less
than 10%. Most of the on-road gasoline vehicles are light duty passenger cars or trucks [< 8,500 lbs
gross vehicle weight rating (GVWR)]. The contribution from on-road heavy-duty gasoline vehicles
(8,501 – 10,000 lbs GVWR) was < 2%. Clark County’s emission contribution by on-road light duty
gasoline vehicles for 1,3-butadiene, benzene, acrolein acetaldehyde and formaldehyde is approximately
39%, 50%, 13%, 1%, and 1%, respectively.
Based on traffic count information received from the Nevada Regional Transporation Commission
(RTC), the annual average daily traffic (AADT) for the I-15 site was approximately 161, 500 (midDecember, 2008 – mid-December, 2009). The AADT during this study period differs from previously
reported AADT (200,000) from Nevada Department of Transportation’s 2007 Annual Traffic Report
(Nevada DOT, 2008). The decrease in ADDT was likely due to an economic recession that occurred
during the study period. The observed fleet mix, based on Nevada RTC data, was 95 % light-duty
vehicles and 5 % heavy-duty vehicles. The vehicle classification estimate is based on vehicle fleet mix
data from an on-road mobile source emissions inventory prepared for Clark County, Nevada which
includes the Las Vegas, NV urban area (Environ International Corp., 2007). The light-duty vehicle
classification includes passenger cars, light-trucks (< 8,500 pounds (lbs) GVWR) and motorcycles.
The heavy-duty truck classification includes heavy-duty single-unit trucks and articulated trucks >
8,501 lbs GVWR, and heavy-duty buses (including school buses and transit buses).
Las Vegas Traffic
Commuter traffic typically exhibits a bi-modal distribution due to home-to-work and work-to-home
commute patterns. However, Las Vegas traffic data exhibited a tri-modal traffic distribution believed
to be the result of several characteristics unique to the area: 1) atypical commuter city; 2) recreation
destination for many travelers; 3) shift changes in Las Vegas are later or earlier in the day depending on
the employer; 4) study site is along an interstate that carries both inter- and intra- state traffic; and 5) I15 is a North American Free Trade (NAFTA) corridor (Figure S2).
Figure S2. Average hourly traffic volume and speed for I-15 site. (Bottom of box plot represents the 25th
percentile; top of box plot represents the 75th percentile; median is the solid line in each box; mean is the dotted
line in each box; whiskers above and below represent 90th and 10th percentiles, respectively; points outside
whiskers represent outliers -- JMP Version 10.0).
Table S3 Clark County (Las Vegas, Nevada) MSAT emissions (U.S. EPA, 2008).
2008 National Emissions Inventory
Nation (U.S.)
Pollutant
Total
(tons/year)
1,3-Butadiene
Benzene
Acrolein
Acetaldehyde
Formaldehyde
52,971
260,602
43,243
777,171
1,230,840
On-Road
(tons/year)
On-Road
% of total
12,543
85,872
2,799
31,017
47,711
24
33
6
4
4
On-Road
Gasoline
(tons/year)
11,931
83,746
1,309
21,737
27,159
On-Road Gasoline
% of Total
On-Road Diesel
(tons/year)
On-Road Diesel
% of Total
23
32
3
3
2
612
2,126
1,491
9,280
20,561
1
1
3
1
2
40
52
13
1
2
1
2
2
8
19
1
<1
9
<1
<1
Clark County
1,3-Butadiene
Benzene
Acrolein
Acetaldehyde
Formaldehyde
77
721
23
3,792
5,310
32
377
5
56
89
42
52
22
1
2
31
375
3
47
70
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