United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-93/019 March 1993
&EPA Project Summary
Characterization of PM-10
Emissions from Antiskid
Materials Applied To Ice and
Snow-Covered Roadways
John S. Kinsey
Several areas of the U.S. in violation
of the National Ambient Air Quality
Standard for PM-10 (participate matter
with diameters < 10 IJJTI) have conducted
studies that have Identified the resus-
pension of antiskid material applied to
paved roadways as an important source
of PM-10. The application of antiskid
materials creates a temporary but sub-
stantial increase in the amount of fine
part leu late on the road surface over
and above that which Is normally
present. Measured emission data are
lacking for all types of antiskid materi-
als; therefore, an appropriate field pro-
gram whose objective was to establish
a predictive model for PM-10 emissions
was undertaken. A source-oriented
emissions sampling procedure was
conducted on a section of US 53 just
west of Duluth, MN, during March/April
of 1992. The measured emission fac-
tors varied from 1 to 11 g/VKT (vehicle
kilometer traveled) for the three tests
conducted. The data were not sufficient,
however, to develop any specific cor-
relation between the measured emis-
sion factors and source parameters.
The only general observation made was
PM-10 emissions appear to increase
with the amount of antiskid material
applied. A comparison of measured
emission factors with those predicted
by an EPA compilation of air pollutant
emission factors (AP-42) indicated that
most of the measured factors are higher
than those that would be predicted from
silt-loading values alone. Due to the
marginal test conditions during storms,
no definitive assessment of this in-
crease can be made until additional
data are obtained.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key find-
Ings of the research project that Is fully
documented In a separate report of the
same title (see Project Report ordering
Information at back).
Introduction
Several areas of the U.S. in violation of
the National Ambient Air Quality Standard
(NAAQS) for PM-10 (airborne particles <10
u,m in diameter) have conducted studies
to determine the sources of these emis-
sions. One source of PM-10 emissions
identified in these studies is the
resuspension of antiskid material applied
to paved roadways. Antiskid materials may
consist of abrasives (e. g., sand, stone, or
cinders applied to the road surface to im-
prove traction) or deicers, which restore
pavement traction by preventing the for-
mation of ice films, weakening the ice/
pavement bond, and/or by melting ice and
snow.
The application of antiskid materials cre-
ates a temporary but substantial increase
in the amount of fine particles on the road
surface over and above that which is nor-
mally present. Prior research has estab-
lished a direct relationship between the
loading of silt-size fines (particles < 75 \im
in physical diameter) and the PM-10 emis-
sion generated by vehicular traffic. "The
empirical relationship between silt loading
and PM-10 emissions is reflected in EPA-
Printed on Recycled Paper
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recommended PM-10 emission factors for
paved urban roads.
In a recent EPA study, a literature
search, an engineering analysis, and a
laboratory testing program were performed
to provide air pollution control agencies
with information on how to identify an ap-
propriate antiskid material that is both du-
rable and effective and produces lower
PM-10 emissions. The primary objectives
of this study were to provide guidance on
methods to determine (a) the physical
properties and durability of antiskid mate-
rials selected for use on ice- and snow-
covered roadways, and (b) criteria for
defining the elements of an effective PM-
10 emission control strategy associated
with use of antiskid materials.
Although the above study provided guid-
ance for the selection of antiskid materi-
als, no direct information was developed
regarding the actual PM-10 emissions re-
lated to their use, the changes in surface
silt loading resulting from such applica-
tion, or the degree of control actually
achieved by compliance with the material
selection criteria developed in the study.
Measured emissions data are lacking for
all types of antiskid material, but deicing
chemicals have received the least amount
of attention. Therefore, an appropriate field
program was needed to establish a suit-
able method for predicting PM-10 emis-
sions from the use of antiskid materials.
This is the primary objective of the work
reported here.
Source-oriented emissions sampling
was employed in the program using Mid-
west Research Institute's (MRI's) "expo-
sure profiling" approach. The data obtained
by this technique were coupled with the
results of road surface sampling and ma-
terials application data in an attempt to
develop a method for predicting PM-10
emissions.
Site Selection
The original test site was located on
northbound US 53 at Mile Post (MP) 13.35
(or approximately Station No. 452+50).
This particular location has good orienta-
tion with respect to the wind direction an-
ticipated for periods after storms, good
exposure to ambient winds (i.e., lack of
trees in the upwind direction), and a rela-
tively flat median for installation of the air-
sampling equipment. However, due to the
mild winter in Duluth, the original test site
could not be used. The site was selected
on the assumption that the ground would
remain frozen throughout the sampling
period, allowing equipment to be safely
placed on the median. When the ground
remained thawed, the sampling site was
moved approximately 1/4 mi (0.4 km)
northbound (i.e., to the west) to an area
near the intersection of US 53 with a
county road. This area provided a firm
surface for the sampling equipment but
had a substantial stand of trees bordering
the northern portion of the right-of-way
which did not conform to criteria estab-
lished by MRI for exposure profiling. For
this and other related reasons, only one
of the three test series was conducted
under suitable conditions with respect to
wind speed and direction. This noncom-
pliance with established criteria adversely
affected data quality as discussed below.
Overall Study Design
The source-directed field sampling con-
ducted in this study employed the expo-
sure profiling approach to quantify source
emission contributions. The exposure pro-
filing technique for particulate source test-
ing is based on the isokinetic profiling
concept used in conventional (stack) test-
ing. The passage of airborne pollutant im-
mediately downwind of the source is
measured directly by means of simulta-
neous multipoint sampling over the effec-
tive cross section of the dust source plume.
This technique uses a mass flux mea-
surement scheme similar to EPA Method
5 stack testing rather than requiring indi-
rect emission rate calculation through the
application of a generalized atmospheric
dispersion model.
Air Sampling Equipment
For measurement of particulate emis-
sions from the test road, a vertical net-
work of samplers (Table 1) was positioned
5 m downwind and 10 m upwind from the
edge of the pavement. Four downwind
vertical sampling arrays (D1 through D4)
and two vertical upwind arrays were used.
Three of the downwind arrays (D1, D3,
and D4) and one upwind array (U2) made
use of high-volume (hi-vol) air samplers
equipped with constant-flow electronic con-
trollers and cyclone pre-separators. The
remaining two arrays (D2 and U1) used
hi-vols equipped with Wedding PM-10 in-
lets and critical orifice flow controllers.
Testing Procedures
Prior to actual sample collection, a num-
ber of decisions were made as to the
potential for acceptable source-testing con-
ditions. These decisions were based on
forecast information obtained either from
the local U.S. Weather Service office and/
or from the Roadway Weather Information
System (RWIS) located at the site. If con-
ditions were considered acceptable, the
sampling equipment was prepared for test-
ing. Pretest preparations included calibra-
tion of the various air sampling instruments
and insertion of filters. All sampling activi-
ties followed quality control (QC) proce-
dures approved by EPA prior to testing.
The particulate samples were collected
on Type AH grade glass fiber filters. The
filters were analyzed gravimetrically at a
constant temperature and humidity in a
Table 1. Sampler Deployment
Sampler array ID
-j-j~
U1
U2
D1, D3, D4
D4
D4
D2
' Certain downwind sat
No. of
instruments
1
2
4
2
1
1
mnlinn Ofininmont muM nnt K
Measurement
height(s) (m)
—3
1.5,3
1, 3, 5, 7
1,5
3
2.5
Type of sampler
or instrument
Hi-vol +
Wedding inlet
Hi-vol + Cyclone
Hi-vol + Cyclone
Warm wire
anemometer
Wind vane
Hi-vol +
Wedding inlet
Parameter(s)
measured
PM-10, Pb
PM-10
PM-10, Na+,CI
(Selected arrays
only)
Wind velocity
Wind direction
PM-10, Pb
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special laboratory. Selected filters were
also extracted and chemically analyzed
by an independent laboratory to deter-
mine the concentration of chloride (Cr),
sodium (Na*), or lead (Pb) in the particu-
late sample collected. Appropriate quality
assurance/quality control (QA/QC) proce-
dures were used throughout all sample
analyses.
Ancillary Sampling and
Analysis
The types of ancillary samples and in-
formation collected in the program fall into
two broad categories: antiskid materials
and roadway surface samples, and source
activity levels. Each is described below.
In conjunction with the emissions tests,
samples were taken of the antiskid mate-
rial (abrasive/rock salt mix and straight
rock salt) applied to the road and the dust
remaining on the surface after it dried.
These samples were needed not only to
evaluate the performance of existing emis-
sion models but also to develop improved
models for antiskid materials. Antiskid
samples were analyzed for silt and mois-
ture content as well as a number of key
physical and chemical properties thought
to be important in the generation of silt
loading (e. g., mass of material < 75 u,m in
physical diameter) on the road surface.
Road surface samples were analyzed for
silt content using established MRI proce-
dures.
Source extent and activity data were
collected with a variety of tools. For ex-
ample, in addition to visual observation
and note taking, pneumatic traffic counters
were used to determine source activity on
US 53. A radar gun was used to deter-
mine the average speed of vehicles pass-
ing the sampler array.
In conjunction with the program, de-
tailed information was collected indepen-
dently by the Minnesota Department of
Transportation (MNDOT) on the condition
of the weather and pavement during the
course of the storm, the types and amounts
of antiskid materials applied to the test
road, and a general indication of the re-
sidual deicing chemical on the road sur-
face at various times. These data were
used to augment the information obtained
on source activity mentioned above. Addi-
tional surface sampling was conducted
between storms to develop a silt-loading
"history" during data analysis.
Calculation Procedure
To calculate emission rates from the
measured PM-10 concentrations (mass/
volume), a conservation of mass approach
was used. The passage of airborne par-
ticulate (i.e., the quantity of emissions per
unit of source activity) was obtained by
spatial integration of distributed measure-
ments of exposure (mass/area) over the
effective cross section of the plume. Ex-
posure is the point value of the flux (mass/
area-time) of airborne paniculate integrated
over the time of measurement, or equiva-
lent ly, the net paniculate mass passing
through a unit area normal to the mean
wind direction during the test. To be con-
sistent with the NAAQS, all concentra-
tions and flow rates were expressed in
standard conditions (25°C and 101 kPa or
77°F and 29.92 in. Hg).
Field Sampling Program
Source Description and Activity
The test site used in the experimental
program was located on northbound US
53 on the outskirts of metropolitan Duluth,
MN. US 53 is an unlimited-access, four-
lane, high-speed roadway carrying com-
muter traffic to and from Duluth at an
approximate volume of 5,000 vehicles/day.
Data collected during field sampling
showed that most traffic was two-axle,
light-duty vehicles traveling between 88
and 97 km/h (55 and 60 mph). Normal
surface loadings, determined both visually
and by sampling, were generally very low,
with silt loadings in the range of 0.2 g/m2.
Exposure profiling was performed after
two minor storms that occurred on April
10, and on April 21 and 22, 1992. One
test series was conducted on April 11,
with additional testing on April 23 and 26.
During the April 10 storm, approximately
4 to 6 in. (10 to 15 cm) of wet snow fell on
US 53 in 24 h. Four applications of an
abrasive/salt mixture were made to the
northbound lanes over a period of ap-
proximately 10 h totaling 395 kg/lane-km
(1,400 Ib/lane-mi). During the second
storm, a combination of wet snow and
freezing rain fell during approximately a
36-h period. In this case, only one appli-
cation of 197 kg/lane-km (700 Ib/lane-mi)
was made to each lane especially for test
purposes.
As determined in previous research, the
application rates used by MNDOT are far
below those of most other transportation
agencies. Also, much of the material ap-
plied was either cast off by the snow plow
during clearing operations or eliminated
by melted precipitation. The material that
remained on the surface was quickly lost
to the atmosphere by the action of pass-
ing vehicles. Thus, surface loadings were
generally low, with higher loadings ob-
served in the passing (left) lane, com-
pared to the driving (right) lane.
Exposure Profiling Results
The results of the three PM-10 expo-
sure-profiling tests are shown in Table 2.
These results were calculated using the
outcome of the gravimetric analyses per-
formed to obtain the measured (i.e., blank-
corrected) PM-10 concentration at each
sampling location. Net (i.e., upwind-cor-
rected) PM-10 concentrations were then
determined at each vertical sampling
height by subtracting estimates from a
straight line fit of the measured upwind
concentrations. (Note that net concentra-
tions were calculated only for arrays with
adequate information for integration pur-
poses.) Using these net concentrations,
the PM-10 exposure was calculated for
each measurement location and exposure
integration performed using a two-step pro-
cess. Finally, PM-10 emission factors were
calculated from the data.
Results of Chemical Analyses
As mentioned above, selected filters (in-
cluding blanks) were submitted for chemi-
cal analysis for either Pb or Na* and Cr
content. The concentration of paniculate
Pb was determined both upwind and down-
wind of the road during Tests AY-4 and
AY-5, using samples collected by the two
Wedding PM-10 instruments. (Similar
analyses could not be performed for Test
AY-3 due to a downwind sample invali-
dated by generator problems.) In the case
of Na* and Cr, filter sets from one down-
wind profiler array for each of the three
tests were submitted for chemical analy-
sis. The purpose of these analyses was to
determine the relative contribution of rock
salt to the total PM-10 emissions from the
roadway.
As shown by the experimental data, the
analyte mass found on most of the filters
does not exceed the blank values for any
of the three species. Of the few filters
which show a net increase in analyte mass
over the blank value, the quantity deter-
mined is generally so slight as to be negli-
gible. Therefore, for the purpose of this
study, it was assumed that the contribu-
tion of both Pb and NaCI to the total PM-
10 emissions from the road was not
significant and thus could be ignored. For
this reason, no specific emission factors
were developed for either Pb or NaCI in
the current program.
Results of Ancillary Sampling
and Analysis
Samples of both the abrasive/rock salt
mixture and straight rock salt were col-
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Table 2. Results of Emission Factor Calculations'
Run
No.
AY-3
AY -4
AY-5
Array
No.
""" f*> J"""
D-1
D-4
D-1
D-4
Sampler
height
(m)
1
3
5
7
1
3
5
7
1
3
5
7
1
3
5
7
NetPM-10
concentration
(\ig/std m3)"
26.9
14.5
-
0
79.8
28.8
0
0
31.2
19.6
1 .11
0
20.4
7.8
4.5
3.3
Wind
speed
(m/s)
as
(5.4)
6.1
(6.7)
3.9
(5.7)
6.6
(7.3)
0.58
(1.0)
1.2
(1.4)
1.4
(1.7)
1.9
(2.1)
NetPM-10
exposure
(lig/cm>)
109
83.2
(41.6)
0
338
178
0
0
6.84
7.41
0.50
0
37.7
17.5
11.3
9.14
Integrated No. of
exposure vehicle
(m-\ig/cm*) c passes
459 1,175
1,038 983
31.8 220
149 650
PM-10
emission
factor
(gWKT)
3.91
10.6
1.44
2.29
1 Parentheses denote inter/extrapolated values. ~~~ — — —
, w^, ~, ™u OUWM «m,u,ai ow ** u»w trm» uo mssn measured oownwina ana upwina concentrations. Upvrind data inter/extrapol
"" °'^^^ fmm0to1m ^9*. with Simpson's rule used for integration be^een
lected from the MNDOT storage piles and/
or spreader trucks. These samples were
then analyzed for moisture and silt con-
tent as well as various key material prop-
erties.
Using the data obtained for the abra-
sive/salt mixture, a comparison was made
of properties with EPA material selection
criteria. This comparison showed that the
abrasive/salt mixture used by MNDOT did
not meet three out of the four key param-
eters thought to be important for high ma-
terial durability. For this reason, the
abrasive/salt mixture analyzed in the cur-
rent program was classified as being of
questionable quality, based on the results
of previous testing.
Road surface sampling was also per-
formed throughout the period that field
testing was attempted in Duluth, MN.
Samples were collected and analyzed to
determine silt loading using accepted pro-
cedures. Surface samples were collected
from both the driving (right) and passing
(left) lane on the northbound and
southbound sides of the median near the
air sampling site with the majority of the
sampling performed on the northbound
lanes.
Using the silt loading data. PM-10 emis-
sion factor estimates were calculated for
the various samples using the AP-42 pre-
dictive model. Emission factors were pre-
dicted for both northbound (abrasive/salt
mixture) and southbound (rock salt only)
lanes in terms of grams per vehicle kilo-
meter traveled (g/VKT).
As shown in Table 3, predicted emis-
sion factors, based on silt-loading data,
were generally low, ranging from less than
1 to a maximum of 4 g/VKT. The highest
emission factors (resulting from the high-
est silt loadings) are for samples collected
from the northbound lanes (abrasive/salt
mixture) after a fairly major storm on Feb-
ruary 24, 1992. (Note that this storm oc-
curred priono field testing. After that time,
the predicted emissions generally drop to
< 1 g/VKT until the next storm in early
April. This decrease in loading would be
expected due to the effects of traffic, which
tends to reestablish a silt-loading "equilib-
rium" on the road surface after external
influences (e.g., the application of antiskid
material) have been eliminated. As also
found, the estimated emission factors are
of the same approximate magnitude as
the test results provided in Table 2 This
lends some additional credibility to the
data obtained by exposure profiling in the
current study.
Discussion of Results
As shown by the above test results, the
measured emission factors varied from 1
to 11 g/VKT for the three tests conducted.
The data were not sufficient, however, to
develop any specific correlation between
the measured emission factors and source
parameters such as quantity of antiskid
material applied, time since application,
and silt loading. The only general obser-
vation that can be made from the data is
that the PM-10 emissions appear to in-
crease with the amount of antiskid mate-
rial applied during the two storms tested
(i.e., the emission factors for Test AY-3
are higher than for Tests AY-4 and AY-5).
(Also note that Test AY-5 had the most
acceptable wind conditions of the three
tests conducted and thus represents the
most reliable emission factor determined
in the study.) Otherwise, the results do
not seem to follow a consistent relation-
ship. A major cause for the lack of asso-
ciation was the marginal test conditions
discussed above.
A comparison of the measured emis-
sion factors (Table 2) with those predicted
by the current AP-42 equation (Table 3)
also yields some interesting results. With
only a relatively few exceptions, most of
the measured factors are higher than those
which would be predicted from silt-loading
values alone In the case of the test (i.e.,
northbound) lanes themselves, the mea-
sured factors either equal or exceed the
lane average emissions predicted by the
AP-42 equation, except for the February
26 samples that were collected after a
fairly major storm. This suggests that the
application of antiskid material results in a
short-term increase in PM-10 emissions
from the roadway in an amount greater
than that which would be predicted by silt
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Table 3. Predicted PM- 10 Emission Factors for Measured Surface Silt Loadings •
Date
2/26
2X8
3/2
3/11
3/19
4/1
4/22
4/24
Lane sampled
NB— Driving
NB— Passing
SB — Driving
SB— Passing
NB— Driving
NB— Passing
SB— Driving
SB— Passing
NB— Driving
NB— Passing
SB— Driving
SB — Passing
NB— Driving
NB— Passing
SB— Driving
SB— Passing
NB— Driving
NB— Driving *
NB— Passing"
NB— Driving "
NB— Passing *
NB— Driving
NB — Passing
SB-Driving and Passing
Road surface silt
loading (g/nf)
1.04
0.501
0.529
0.271
0.341
0.0262
0.445
0.295
0.0701
0.0661
0.0382
0.122
0.200
0.164
0.208
0.354
0.0431
0.0788
0.156
0.0618
0.544
0.150
0.133
0.0526
Predicted
PM-10 emission
factor (g/VKT)
4.10
2.28
2.38
1.39
1.68
0.215
2.08
1.50
0.473
0.452
0.291
0.738
1.10
0.935
1.13
1.73
0.321
0.520
0.900
0.428
2.44
0.870
0.790
0.376
• PM- 10 emission factors predicted using the AP-42 predictive equations and silt-loadings obtained in
the program.
" Loadings measured after application of antiskid material.
loading alone. Although no definitive as-
sessment of this increase can be made
based on available data, the PM-10 emis-
sions could be almost a factor of 3 higher
(i.e., 11 vs. 4 g/VKT) than would be pre-
dicted from the silt loading. This propor-
tional increase in emissions is considerably
higher than the precision factor of ap-
proximately 2 for the current AP-42 pre-
dictive equation and thus worthy of further
study. Therefore, a more explicit evalua-
tion would help determine the extent of
the emissions increase due to the appli-
cation of antiskid material to paved road-
ways.
Conclusions
The following conclusions were reached
as a result of the current study:
1. Because the measurements con-
ducted were performed under diffi-
cult environmental conditions that
did not meet all of the applicable
QC criteria for exposure profiling,
data quality was adversely affected.
2. Although the emission factors de-
termined in the program ranged
from 1 to 1 1 g/VKT for the three
tests conducted, these values
should be used with extreme cau-
tion due to the lack of suitable test
conditions during sample collection
and resulting poor data quality.
3. The contribution of both particulate
Pb and NaCI to the total PM-10
emissions from the road did not
appear to be significant based on
the limited chemical analyses per-
formed during the program.
4. The dry silt loadings determined on
US 53 tended to (a) be relatively
low and (b) drop off rapidly after a
storm, which is typical of high-speed
roadways. The amount of silt avail-
able for resuspension was also
found to be very low due to the
minimal application of antiskid ma-
terial during the experimental pro-
gram.
5. Emission factors determined in the
program were generally higher than
those predicted by the current AP-
42 equation, based on road sur-
face silt loading. The magnitude of
this increase could not be defini-
tively determined from available
data, but it may be almost a factor
of 3.
•U.S. Government Printing Office: 1993 — 750-071/60218
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J. S. Kinsey is with Midwest Research Institute, Kansas City, MO 64110-2299.
Charles C. Masseris the EPA Project Officer (see below).
The complete report, entitled "Characterization ofPM-10 Emissions from Antiskid
Materials Applied To Ice and Snow-Covered Roadways," (Order No. PB93-
150209; Cost: $19.50; subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
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