United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S2-84-027 Apr. 1984
Project Summary
Extended Evaluation of Unpaved
Road Dust Suppressants in the
Iron and Steel Industry
Gregory E. Muleski, Thomas Cuscino, Jr., and Chatten Cowherd, Jr.
This study involved the measurement
of the long-term control effectiveness
of various dust suppressants used to
mitigate particulate emissions from
vehicular traffic on unpaved roads in the
iron and steel industry- Control effec-
tiveness values were determined by mea-
suring emissions, using an exposure pro-
filing technique, before and after con-
trol application. Control effectiveness
was determined for total particulate
(TP) and for three particle size (aero-
dynamic diameter) fractions: § 1Sfjm,
inhalable particulate (IP); S10/um (PMio);
and ^ 2.5 /urn, fine particulate (FP).
Parameters affecting the cost-effec-
tiveness of unpaved road dust suppres-
sants were also quantified, and the
trace element composition of uncon-
trolled unpaved road surface material
and airborne dust emissions was exam-
ined.
Three dust suppressants, used to
reduce unpaved road emissions, were
evaluated: (1) a 20% solution of Petro
Tac (an emulsified asphalt) applied at
3.2 l/m2 (0.70 gal/yd2); (2) water
applied at 2.0 l/nT (0.43 gal/yd2); and
(3) a 20% solution of Coherex® ( a
petroleum resin) applied at 3.8 l/m2
(0.83 gal/yd2) followed by a repeat
application of 4.5 l/m2 (1.0 gal/yd2) of
12% solution 44 days later. Twenty-
nine tests of controlled and uncontrolled
particulate emissions from vehicular
traffic on unpaved roads were conducted.
A decay in control effectiveness, as a
function of vehicle passes after applica-
tion, was measured for the dust suppres-
sants tested. The asphalt emulsion
showed an effective lifetime ranging
from about 50,000 vehicle passes for
control of FP emissions to over 100,000
vehicle passes for control of TP emissions.
Unlike the asphalt emulsion, the petro-
leum resin appeared to control particu-
late emissions of different size fractions
consistently throughout its lifetime of
about 7,500 vehicle passes for the first
application. Tests of the reapplication
of the petroleum resin provided strong
indication of a residual effect from the
initial application. The lifetime of the
repeat application ranged from 17,000
passes for FP to 45,000 passes for TP.
Tests of watering of unpaved roads
indicated high initial control efficiency
which decreased at a rate of approxi-
mately 8%/hr. The rate of control
efficiency decay decreased with de-
creasing particle size.
Comparison of optimal cost-effec-
tiveness values for the dust suppres-
sants evaluated and for the road condi-
tions tested indicates that the chemical
techniques can control unpaved road
PMio emissions for 5-50% of the cost of
using water. Essentially linear relation-
ships were found between downwind
airborne and surface aggregate mass
concentrations for most of the trace ele-
ments detected in the chemical analysis
of uncontrolled, unpaved road dust
emissions.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
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Introduction
Previous studies have provided strong
evidence that open dust sources (e.g.,
vehicular traffic on unpaved and paved
roads, aggregate material handling, and
wind erosion) should occupy a prime
position in control strategy development
in the iron and steel industry. This
conclusion has been based on compari-
sons between industry-wide uncontrolled
emissions from open dust sources and
typically controlled fugitive emissions
from major process sources (e.g., steel-
making furnaces, blast furnaces, coke
ovens, and sinter machines). In addition,
preliminary cost-effectiveness (dollars
expended per unit mass of reduced
paniculate emissions) analysis of promis-
ing control options for open dust sources
has indicated that control of these
sources might result in significantly
improved air quality at a lower cost
compared to the control of process
sources.
These preliminary conclusions prompted
this study to gather additional data on
control performance and costs for open
dust sources in the steel industry.
Although testing was conducted at iron
and steel plants, the control efficiencies
presented in this report apply to unpaved
roads in other industries, if the roads
have similar traffic and surface charac-
teristics.
Control efficiency for unpaved roads
can be affected by four broad categories
of variables: (a) time-related variables, (b)
control application variables, (c) vehicle
characteristics, (d) characteristics of the
surface to be treated, and (e) particle size
range being considered. The emphasis of
this effort was on (a), time-related
variables.
Because of the finite durability of all
surface-treatment control techniques,
ranging from hours (watering) to years
(paving), it is essential to relate an
efficiency value to a frequency of applica-
tion (or maintenance). For measures of
lengthy durability, the maintenance
program required to sustain control
effectiveness should be indicated. One
likely pitfall to be avoided is using field
data collected soon after control measure
application to represent the average
control efficiency over the lifetime of the
measure.
The climate, for the most part, acceler-
ates the decay of control performance
adversely through weathering. For exam-
ple, freeze/thaw cycles break up the
crust formed by binding agents; heavy
precipitation washes away water-soluble
chemical treatments like lignin sulfonates
or salts; and solar radiation dries out
watered surfaces. On the other hand,
light precipitation might improve the
efficiency of water extenders and hygro-
scopic chemicals like calcium chloride.
The average control efficiency, C(T),
is given by
T
C(T)=J_5- c(t)dt
T o
where: C(T)=Average control efficiency
during period ending T days
after application (percent)
c(t)=lnstantaneous control effi-
ciency at t days after appli-
cation (percent)
T=Time period over which
average control efficiency
is desired (days)
The overall objective of this study was
to provide data that document the mass of
paniculate emissions (in several size
ranges) generated by vehicular traffic on
controlled unpaved roads in the iron and
steel industry Most of the data were to
provide control efficiencies for common
road dust suppressants over the lifetime
of each control measure. Thus, the long-
term control efficiency decay function
associated with each dust suppressant
applied to unpaved roads formed the
primary goal of this study. For emphasis,
the chemical control measures were
applied following the manufacturer's
recommendations for dilution ratio and
application intensity; as such, data
presented in this report are directly
applicable only to the dilution ratios and
application intensities tested.
Secondary objectives of this study were:
(a) calculating the cost-effectiveness of
measures designed to reduce unpaved
road dust emissions; (b) comparing the
emission factors obtained with simulta-
neously operated 6-m and 10-m profiling
towers; and (c) determining the trace
element composition of particulate
emissions from unpaved roads in the iron
and steel industry.
Summary and Conclusions
The purpose of this study was to
measure the long term control efficiency
(effectiveness) of various dust suppres-
sants used in the iron and steel industry
to mitigate particulate emissions from
vehicular traffic on unpaved roads.
Control efficiency values were determined
not only for total paniculate (TP), but also
for particles less than 15 //m in aerody-
namic diameter (inhalable particulate, IP),
less than 10/um in aerodynamic diameter
(PMio), and less than 2.5 pm in aerody-
namic diameter (fine particulate, FP). In
addition to control efficiency determina-
tion, parameters affecting the cost-
effectiveness of unpaved road dust
suppressants were quantified, and the
trace element composition of uncontrolled
unpaved road surface material and
airborne dust emissions was examined.
Vehicular traffic on unpaved roads was
the sole concern of this study because
this source was estimated to contribute
56% of the open source suspended
particulate emissions in the iron and
steel industry.
The exposure profiling method devel-
oped by MRI was the technique utilized to
measure uncontrolled and controlled
emission factors for vehicular traffic on
unpaved roads. Exposure profiling of
roadway emissions involves direct iso-
kinetic measurement of the total passage
of open dust emissions approximately 5
m downwind of the edge of the road by
means of simultaneous sampling at four
points distributed vertically over the
effective height of the dust plume.
Downwind particle size distributions
were measured at the 1.5 and 4.5 m
heights using cyclone precollectors
followed by parallel-slot cascade irrTpac-
tors. Upwind size distributions were also
determined using a cyclone/impactor
combination.
Twenty-nine tests of controlled and
uncontrolled particulate emissions from
vehicular traffic on unpaved roads were
conducted. Six of these provided uncon-
trolled baseline emissions data necessary
to determine control efficiency and cost-
effectiveness.
Three dust suppressants used to
reduce unpaved road emissions were
evaluated.
1. A 20% solution of Petro Tac (an
emulsified asphalt) applied at an
intensity of 3.2 l/m2 (0.70 gal/yd2).
2. Water applied at an intensity of 2.0
l/m2 (0.43 gal/yd2).
3. A 20% solution of Coherex® (a
petroleum resin) applied at an
intensity of 3.8 l/m2 (0.83 gal/yd2),
followed by a repeat application of
4.5 l/m2 (1.0 gal/yd2) of 12%
solution 44 days later.
The results in this report are directly
applicable only to these dilution ratios
and application intensities. The chemical
dust suppressants were applied in
quantities recommended by the manufac-
turers. These quantities were, in general,
much higher than those currently used at
iron and steel plants.
Table 1 presents estimated lifetimes
and source/control parameters for the
dust suppressants evaluated. The lifetimes
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Table 1 . Control Efficiency Decay
Dust suppressant
Asphalt Emulsion
(initial application)
3.2 l/m of 20% solution
in water
Petroleum Resin
(initial application)
3.8 l/m at 20% solution
in water
Petroleum Resin
(reapplication)
4 5 l/m2 of 12% solution
in water
Water
1.9 l/m2
Rates
Mean
vehicle
weight
(Mg)
27
34
39
44
Mean Particle
No. of size
wheels range
9.2 TP
IP
FP
6.2 TP
IP
FP'
6.0 TP
IP
PMio
FP
6.0 TP
IP
PMio
FP
Estimated
lifetime
(vehicle
passes)
125.000
77,000
91,000
53.000
7,100
7,100
7,700
7,700
45,000
26,000
23,000
17,000
480
530
560
620
given are applicable only to situations
with the same source/control param-
eters. (Lifetime is the time at which a
sufficient number of vehicle passes have
caused the control efficiency to decay to
zero.)
The asphalt emulsion was tested over a
period of about 4 months and nearly
50,000 vehicle passes. Although TP
emissions showed the lowest initial
control efficiency, the control efficiency
values associated with particulate emis-
sions in the smaller size ranges showed a
much greater rate of decay than that for
TP. For example, initial FP control
efficiency was substantially greater than
that of TP, but the FP control efficiency
decay rate was much greater, so that FP
emissions nearly matched the uncon-
trolled state at a time when TP emissions
were still controlled at the 50% level.
The tests of watering of unpaved roads
indicated high initial control efficiency,
which decreased at a rate of approximately
8% per hour. The rate of control efficiency
decay was found to decrease with
decreasing particle size.
The tests of an initial application of a
petroleum resin product did not indicate
significant variation in the control
efficiency decay rate as a function of
particle size range. During each test in
the 41 day period after application, the
measured control efficiency increased
with decreasing particle size. Unlike the
asphalt emulsion, the petroleum resin
appeared to control particulate emissions
of different size fractions consistently
throughout its lifetime. In other words,
the decay rate for the initial application of
the petroleum resin was nearly identical
regardless of the particle size.
The tests of the reapplication of the
petroleum resin provided strong indication
of a residual effect from the initial
application. Figure 1 compares the PMio
control efficiency decay functions for
those associated with the initial and
repeat applications. The rate of decay for
the repeat application was found to be
roughly one order of magnitude less than
that associalecl with the initial application.
Comparisonflnhe surface aggregate size
distribution before and after chemical
retreatment suggests that the bonding
characteristics of the reapplication are
enhanced by a residual effect of the initial
treatment.
Comparison of optimal cost-effective-
ness values for the dust suppressants
evaluated indicates that the chemical
techniques are capable of controlling
unpaved road PMio emissions for 5-50%
of the cost of using water. However, note
that direct comparisons between sup-
pressants are difficult at best, even when
tests are conducted at the same site,
because of changes in vehicle character-
istics, traffic rate, etc. Comparisons
between suppressants evaluated at
different sites are even more formidable
because there are additional uncontrol-
lable variations in road structure and
surface characteristics. Consequently,
there are situations where watering, for
example, may be more cost-effective than
chemical dust suppressants.
Essentially linear relationships were
found between downwind airborne and
surface aggregate mass concentrations
700
90
as
80
70
2 60
50
40
I I
Road originally
treated with 3.8
L/m2 of 20%
solution
i
i
Road retreated
with 4.5 L/m2
of 12% solution
Average vehicle
Weight = 36 Mg
Average No.
of Wheels = 6.1
l
0 1500 3000 4500 6000 7500
Vehicle Passes After Original Application
L
_L
JL
J
0 20 40 60 80
Time After Original Application, days
Figure 1. Comparison of the control per-
formance for PM^o of initial and
repeat applications of a petrole-
um resin illustrating the residual
effect.
for most of the trace elements detected in
the chemical analysis of uncontrolled,
unpaved road dust emissions. Because of
these relationships, it appears possible to
economically estimate airborne elemental
mass concentrations by examining the
corresponding concentrations in the
surface material. However, more data are
required to substantiate this approach.
In a comparison designed to accentuate
the variation between measurement-
based emission factors using 10m and 6
m profiling towers, the percent difference
was 10-17%. Because the small differ-
ences found in this worst-case compari-
son are within the experimental accuracy
of the profiling method, the difficulties in
erecting and operating a 10 m tower at a 5
m distance from the edge of the road are
not justified.
Additional work in the area of open dust
control evaluation would be helpful. To
truly optimize the cost-effectiveness of a
control program designed to meet a
minimally acceptable level of average
control, a range of application intensities
and dilution ratios should be examined.
Ideally, enough data should be collected
to support a mathematical relationship
between average control efficiency and
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application parameters. The values of
application parameters tested should
span the ranges commonly employed in
the iron and steel industry for the most
prevalent dust suppressants. To provide
optimization of control performance for a
given dust suppressant, each control
efficiency decay function should be based
on a minimum of three application
intensities.
Identifying readily quantifiable source
parameters, which can be used as
measures of control effectiveness, would
reduce the expense of the field investiga-
tions required to characterize dust sup-
pressant performance in the iron and
steel industry. This would permit tracking
control performance without labor-
intensive source testing.
Another way to reduce the amount of
costly field tests would be developing and
implementing a laboratory screening
procedure, perhaps involving wind tunnel
exposure of representative samples of
aggregate materials. In addition to wind
forces, the tests could involve simulating
the forces of vehicle tire/road surface
contact. Control performance could be
measured as resistance to loss of
exposed surface materials. Ideally, if a
program adopted for the laboratory
simulation produced the same effective-
ness ranking for the typical chemicals as
that determined by field tests of these
chemicals, it would establish the useful-
ness of the laboratory-based ranking for
application to field conditions.
Gregory E. Muleski, Thomas Cuscino. Jr.. and Chatten Cowherd, Jr., are with
Midwest Research Institute, Kansas City, MO 64110.
Robert C. McCrillis is the EPA Project Officer (see below).
The complete report, entitled "Extended Evaluation of Unpaved Road Dust Sup-
pressants in the Iron and Steel Industry," (Order No. PB 84-154 350; Cost:
$16.00, 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:
Industrial Environmental 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
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