United States National Risk Management

Environmental Protection Research Laboratory

Agency Cincinnati, OH 45268

EPA Project Summary

Research and Development EPA/600/SR-95/119 February 1996

Several areas of the country in violation of the National Ambient Air Quality

Standard for PM-10 have conducted

studies identifying the resuspension of

antiskid materials from urban paved

roads as an important emission source.

In this study, a field sampling program

was conducted on 47th Street in Kansas City, MO, during February and

March 1993 to quantify the PM-10 emissions associated with the use of rock

salt (NaCl) for ice and snow control. A

baseline test was conducted in September 1993. The emissions were determined using exposure profiling. The

measured emission factors spanned the

following ranges, in grams per vehicle

kilometers traveled (g/VKT):

• Total PM-10: 0.2 to 1.7 (winter

tests); 3.9 to 4.9 (September test)

• PM-10 lead: 7.5 (10)-5 to 4.5 (10)-4

(winter tests)

• PM-10 NaCl:0.014 to 0.039 (winter

tests)

The winter emission factors for total

PM-10 determined in this study were

about an order of magnitude lower than

those measured in a 1992 Duluth study

which utilized a 90% sand/10% salt

antiskid material. The studies concluded that the sand from the antiskid

material mixture that remained after the

road had dried, constituted most of the

silt loading and, therefore, the PM-10

emission impact. The rock salt, removed from the road mostly in the melting slush, contributed only a few percent to the residual silt loading.

This Project Summary was developed

by the National Risk Management ReCharacterization of PM-10

Emissions from Antiskid

Materials Applied to Ice- and

Snow-Covered Roadways—

Phase II

John S. Kinsey

search Laboratory’s Air Pollution Prevention and Control Division, Research

Triangle Park, NC, to announce key

findings 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 country that are in

violation of the National Ambient Air Quality Standard for PM-10 (airborne particles

less than or equal to 10 μmA in diameter)

have conducted studies to determine the

sources of these emissions. One source

of PM-10 emissions identified in a number

of these studies is the resuspension of

antiskid material applied to paved roadways. Antiskid materials may consist of

(a) abrasives, such as sand, stone, or

cinders, applied to the road surface to

improve traction or (b) ”deicers,” which

restore pavement traction by preventing

the formation of ice films, weakening the

ice/pavement bond, and/or melting ice and

snow.

The application of antiskid materials,

especially low durability abrasives, can create a temporary, but substantial, increase

in the amount of fine particles on the road

surface over that which is normally present.

Prior research has established a direct

relationship between the loading of siltsize fines (particles <75μm in physical diameter) and the PM-10 emissions generated by vehicular traffic. The empirical relationship between silt loading and PM-10

emissions is reflected in the EPA-recommended PM-10 emission factors for paved

urban roads. This relationship was developed from a data base encompassing the
2

results of tests conducted under dry conditions at eight sites, ranging from a freeway to a rural town road.

More recently, a revised emission factor model for predicting the PM-10 emissions from paved roads has been incorporated into the 5th edition of EPA report

AP-42. This model is expressed as

(1)

where: E = PM-10 emission factor

(grams per vehicle kilometers traveled—g/VKT)

s = surface silt content (fraction of particles < 75μm

in physical diameter)

L = total road surface dust

loading (g/m2)

W = average weight (tons) of

the vehicles traveling on

the road

The total loading (excluding litter) shown

in Eq. (1) is measured by sweeping and

vacuuming lateral strips of a known area

from each active travel lane. The silt fraction is determined by measuring the proportion of loose dry road dust that passes

a 200-mesh screen, using a modified version of ASTM C 136. Silt loading is the

product of total loading and silt content.

Average vehicle weight is determined from

observations of the mix of traffic on the

road.

To evaluate the applicability of available emission factors to roads treated with

antiskid materials, PM-10 emission testing of a six-lane arterial located in Kansas

City, MO, was conducted. The first testing

phase in February and March 1993 was

devoted to the characterization of emissions from the road after the application

of a common deicer (rock salt) for ice and

snow control. The second testing phase

in September 1993 determined the PM-10

emissions from the same road without the

influence of the deicing chemical. The results of these tests are summarized below.

Site Description

The test site was 47th Street between

Rockhill Road and Oak Street in Kansas

City, MO. This road is a six-lane arterial

maintained as part of Kansas City’s boulevard system. This road is used by commuter traffic to and from a major shopping

and business area of the city at an approximate volume of 30,000 vehicles/ day.

Data collected during field sampling

showed that essentially all of the traffic

was two-axle, light-duty vehicles traveling

at an average speed of 46 km/h (29 mph).

Surface loadings determined both visually and by sampling were generally very

low, with nominal silt loadings of about

0.2 g/m2.

The site was suitable for a number of

reasons, including its east-west orientation with respect to prevailing north-south

ambient winds, good cooperation by the

local transportation agency (City of Kansas City, Parks and Recreation Department), and the relatively high traffic volume during daylight hours. In addition, the

wide median allowed for testing of half the

total road width (one traffic direction),

thereby helping to limit the vertical extent

of the plume at the point of downwind

sampling.

Overall Study Design

The source-directed field sampling conducted in this study employed “exposure

profiling” to quantify source emission contributions. This method is based on the

isokinetic profiling concept used in conventional (stack) testing. The passage of

airborne pollutant immediately downwind

of the source is measured directly by

means of simultaneous multipoint sampling over the effective cross section of

the open dust source plume. This technique, which uses a mass flux measurement scheme similar to EPA Method 5 for

stack testing, does not require an indirect

emission rate calculation through the application of a generalized atmospheric dispersion model.

Air Sampling Equipment

For measurement of particulate emissions from the test road, a vertical network of samplers was positioned 5 m

downwind and 10 m upwind from the edge

of the road. As shown in Tables 1a and

1b, the equipment deployment scheme

made use of three downwind vertical sampling arrays, D1 through D3. Downwind

arrays D1 and D3 (as well as upwind

array U2) used high-volume (hi-vol) air

samplers equipped with cyclone PM-10

inlets and critical orifice flow controllers.

Arrays D2 and U1 used hi-vols equipped

with Wedding PM-10 inlets and critical

orifice flow controllers.

The PM-10 deposits were collected on

either Type AH grade glass fiber on QM-A

microquartz 8- by 10-in filters. Ten percent of the filters taken to the field were

used as blanks.

During the winter tests, the two

vertical profiler arrays (D1 and D3) were

located about 10 m apart. As such, the

profilers can be considered as “collocated”

with comparable measurements made.

During the September test, the two

profilers were located a considerable distance from each other and thus represent

independent measures of road emissions.

Also during the winter tests, the PM-10

samples collected at each height for one

profiler array per test were analyzed for

lead (Pb), sodium (Na+) and chloride (Cl-).

The PM-10 (and lead measurements)

made by the two Wedding reference instruments were used for comparison

against data collected by the cyclone samplers. Standard EPA analytical protocols

and associated QA/QC procedures were

used for this purpose.

Ancillary Data Collection

In conjunction with the emissions tests,

samples of the antiskid material applied to

the road (winter testing only) and the dust

on the road surface were obtained. These

samples were needed to evaluate the

performance of existing emission models.

The samples collected were analyzed for

(a) silt content by dry sieving and (b) percent insoluble matter using ASTM E534,

as an indirect indicator of residual salt on

the road surface.

Vehicle-related parameters were also

obtained using a combination of manual

and automated counting techniques. Pneumatic tube axle counters were used to

obtain traffic volume data. Because these

counters record only the number of passing axles, it was necessary to obtain

manual traffic mix information (e.g., number of axles per vehicle) to convert axle

counts to the number of vehicle passes.

Vehicle mixes were observed visually. In

addition, a radar gun was used during

selected tests to determine the average

speed of vehicles passing the sampler

array.

Finally, detailed information was collected by Kansas City Parks and Recreation Department (KCP&R) personnel on

the weather and condition of the pavement during the course of each winter

storm and on the types and amounts of

deicing chemical applied.

Test Results

During the winter tests, exposure profiling was performed after three storms that

occurred on February 15 and 16; February 25; and March 18 and 16; 1993. After

the February 15 and 16 storm, three tests

were attempted with two of these being

complete runs. For the February 25 storm,

one complete test was performed. During

this particular test, however, the road surface was initially damp and later became

wet with snow melt. Therefore, these particular data were not included in the emission factor calculations. (Note that this run

E = 4.6(

sL

2

)

0.65

(

w

3

)

1.5
3

Table 1a. Sampler Deployment for Winter Tests

Sampler No. of Measurement Type of sampler Parameter(s)

array ID instruments height(s) (m) or instrument measured

U1 1 2 Hi-vol + Wedding PM-10, Pba

Inlet

U2 2 1.5, 3 Hi-vol + Cyclone PM-10, Pbb

D1, D3 4 1, 3, 5, 7 Hi-vol + Cyclone PM-10 + Na+, Cl-,

Pbb (selected

arrays only)

D1 1 4 Wind vane Wind direction

D2 1 2 Hi-vol + Wedding PM-10, Pba

Inlet

D4 2 1, 5 Warm wire Wind velocity

anemometer

a Lead analysis by EPA Method 239.1 (inductively coupled plasma atomic absorption spectroscopy).

b Lead analysis by EPA Method 200.9 (graphite furnace atomic absorption spectroscopy).

Table 1b. Sampler Deployment for September Test

Sampler No. of Measurement Type of sampler Parameter(s)

array ID instruments height(s) (m) or instrument measured

U2 2 3, 5 Hi-vol + cyclone PM-10

D1, D3 4 1, 3, 5, 7 Hi-vol + cyclone PM-10

D2 1 2 Hi-vol + Wedding inlet PM-10

D3 1 4 Wind vane Wind direction

D3 2 1, 5 Warm wire anemometer Wind velocity

D4 1 3 Wind vane/propeller Wind velocity

anemometer and direction

sampled fine salt spray produced by passing vehicles and not particulate matter in

the traditional sense.) The third test followed the March 18 and 19 storm.

In September 1993, one successful test

was performed two days after a major

rain storm. During this test, 47th Street

was used by heavy vehicle traffic exiting

the flood control project located south of

the test site. The heavy trucks exiting the

project caused a substantial increase in

the silt loading measured on the road surface compared to the winter testing. This

increase in silt loading was reflected in

the measured PM-10 emissions as discussed below.

Exposure-Profiling Results

The results of the exposure-profiling

tests performed on the filter samples collected in the field are summarized in Table

2. These results were obtained by first

calculating the blank-corrected PM-10 concentrations at the various sampling locations. The net (i.e., upwind-corrected) PM10 concentrations were then calculated at

each height by subtracting the average of

the upwind concentrations determined by

Array U2. Using these net concentrations,

the net PM-10 exposure was calculated

for each sampler location and the exposure profile was integrated. Finally, PM10 emission factors were calculated from

the data.

As mentioned above, selected filters (including blank filters) from each of the winter tests were submitted for chemical

analysis of Pb, Na+, and Cl- content. The

concentration of Pb in the PM-10 samples

was determined by two methods. In the

first method, filters from the two Wedding

samplers (Arrays U1 and D2) were acid

extracted and analyzed by inductively

coupled plasma spectroscopy (ICP). In the

second technique, filters from one profiler

array (as well as Array U2) for each test

were acid extracted and analyzed by

graphite furnace atomic absorption

(GFAA). Since none of the filters analyzed by the ICP method were above the

instrumental detection limit, only the results of the lead analyses conducted by

GFAA were used to calculate compoundspecific PM-10 emission factors.

For Na+ and Cl-, filter sets from one

downwind profiler array for each test (and

Array U2) were submitted for chemical

analysis. The purpose of these analyses

was to determine the relative contribution

of rock salt to the total PM-10 emissions

from the roadway. NA+ was determined

using flame atomic absorption and C1- by

ion chromatography.

Using the results of the chemical analyses performed, compound-specific PM-10

emission factors were calculated for both

Pb and NaCl. The same calculation procedure outlined previously for total PM-10

was used for this purpose. The emission

factors obtained in this study for Pb and

NaCl are presented in Table 3.

Results of Ancillary Sampling

and Analysis

A sample of rock salt was collected

from the KCP&R storage pile. This sample

was split and analyzed for silt content and

percent insoluble matter. The analytical

results obtained for the antiskid material

samples collected were: silt = 1.6 wt %;

and insolubles = 2.3 wt %.

Road surface sampling was also performed from December 1992 through September 1993. The silt loadings measured

in this period varied over about two orders

of magnitude (0.02 to 1.4g/m2) with the

highest silt loading value obtained in September. Except for the two samples collected in January, the insoluble matter

found in the silt fell within a fairly narrow

range of 91 to 98% (i.e., 2 to 9% water

soluble fraction) regardless of time of year.

Discussion of Results

As shown by the above results, the PM10 emission factors determined from the

wintertime test data are not related to the

amount of NaCl applied to the road surface during each storm tested. This is

consistent with the fact that NaCl constitutes only a minor portion of the surface

silt loading. The NaCl apparently goes

into solution and is largely removed from

the road surface before it dries. The winter surface silt loading consists largely of

insoluble matter not derived directly from

the chemical deicer (rock salt) but instead

from other types of materials. The origin

of this loading may be related to pavement wear and “potholing,” which could

be an indirect result of the deicing chemical used.

A comparison of these results with those

of a 1992 Duluth emission study of the

effects of antiskid abrasives is also of

interest. As can be observed from Table

4, the PM-10 emission factors measured

in 1992 for a sand/ salt mixture (90%

sand/ 10% rock salt) are substantially

higher than those determined after the

application of rock salt in the present study,

by as much as an order of magnitude.

These data would indicate that the application of antiskid abrasives is of far greater

concern in the control of PM-10 emissions

from paved roads than is the case for

chloride deicers.

Finally, a comparison of the measured

PM-10 emission factors with those predicted by Eq. (1) from the silt-loading data
4

Table 2. Results of PM-10 Emission Factor Calculationsa

Measured

PM10

Sampler Net PM10 Wind Net PM10 Integrated No. of emission

Run Array height concentration speed exposure exposure vehicle factor

No. No. (m) (μg/std m3)

b

(m/s) (μg/cm2)

c

(m-μg/cm2)

d passes (g/VKT)e

BC-1 D1 1 8.66 1.8 16.8 44.5 2245 0.20

(2/17/93) 3 2.20 (2.6) 6.18

5 0.0 3.0 0.0

7 0.0 (3.3) 0.0

BC-3 D1 1 12.11 3.4 61.8 224 3577 0.63

(2/19/93) 3 7.13 (3.8) 40.6

5 1.04 3.9 6.08

7 0.25 (4.1) 1.54

D3 1 50.58 3.4 249 606 3552 1.7

3 9.19 (3.8) 50.5

5 3.04 3.9 17.1

7 2.13 (4.1) 12.6

BC-5 D1 1 15.41 1.1 27.7 135 3617 0.37

(3/20/93) 3 7.32 (1.7) 20.3

5 4.06 1.9 12.6

7 1.88 (2.1) 6.44

D3 1 13.33 1.1 24.0 118 3639 0.32

3 6.30 (1.7) 17.5

5 3.92 1.9 12.2

7 1.61 (2.1) 5.53

BC-12 D1 1 241.9 1.0 118 381 969 3.9

(9/16/93) 3 85.18 (1.1) 45.5

5 40.08 1.2 23.4

7 20.15 (1.2) 11.8

D3 1 177.1 1.1 97.0 497 1016 4.9

3 117.2 (1.3) 75.9

5 57.07 1.3 37.0

7 36.51 (1.4) 25.5

(9) (16.00) (1.5) 12.0

a

() indicates inter/extrapolated value.

b Net concentration calculated as difference between average upwind concentration (Array U2) and downwind concentration at each sampler height.

c Rounded to three significant figures.

d

Integration scheme assumes constant exposure from 0 to 1 m height with Simpson’s approximation used for integration between 1 m and effective plume height (H).

e Rounded to two significant figures.

Table 3. Results of Compound-Specific PM-10 Emission Factor Calculations (Winter Tests)a

Array No. of vehicles Lead emission NaCI emission

Run No. No. passes factor (g/VKT) factor (g/VKT)

BC-1 D1 2,245 Nil 0.039

(2/17/93)

BC-3 D3 3,552 7.05 (10)-5 0.021

(2/19/93)

BC-5 D1 3,617 4.3 (10)-4 0.014

(3/20/93)

a

Includes only Pb or NaCl found in particles 10 μm in aerodynamic diameter. Rounded to two significant figures.
5

Table 4. Emission Factors Developed During 1992 Duluth Testing Programa

No. of vehicle PM-10 emission factor

Run No. Array No. passes (g/VKT)

AY-3 D-1 1,175 3.91

D-4 983 10.6

AY-4 D-1 220 1.44

AY-5 D-4 650 2.29

a From Kinsey (1993).

Table 5. Ratio of Predicted to Measured PM-10 Emissions

Ratio of

Measured Measured Predicted predicted

silt PM-10 PM-10 to

1993 Run Array loading emission emission factor measured

date No. No. (g/m2) factor (g/VKT) (g/VKT) emissions

2/17 BC-1 D1 0.061a 0.20 0.26 1.3

3/20 BC-5 D1 0.55 0.37 1.08 2.9

D3 0.32 3.4

9/16 BC-12 D1 1.44 3.9 3.7 0.95

D3 4.9 0.76

a Determined on 2/18/93.

yields some interesting results. As shown

in Table 5, the measured emission factors

agree well with the predicted values, taking into account the confidence interval

associated with Eq. (1). The 1ó confidence interval for Eq. (1), which is a good

measure of its average uncertainty of prediction, is a factor of 4.2.

Study Conclusions

The winter PM-10 emission factors determined in this study of the effects of a

chemical deicer (NaCl) were generally low,

ranging from 0.2 to 1.7 g/VKT. In contrast,

the winter emission factors measured in

the earlier Duluth study of the effects of

antiskid abrasives were about an order of

magnitude higher. Thus the use of antiskid

abrasives is much more significant than

the chemical deicer, in terms of PM-10

emission impact.

Rather than increasing the surface silt

loading, NaCl aids in cleaning the road by

forming slush which is either picked up on

vehicle underbodies, cast aside, or removed as runoff. Little NaCl is left in the

residual silt loading once the road surface

has dried. Insoluble materials from other

sources (possibly including pavement deterioration enhanced by the NaCl) drive

the PM-10 emission rate.

The compound-specific PM-10 emission

factors for Pb and NaCl, as determined in

the winter testing, ranged from 7.5 (10)-5

to 4.5 (10)-4 g/VKT and 0.014 to 0.039 g/

VKT, respectively. Due to the low magnitude of these emission factors, the contributions of both analytes to the total PM10 emissions from the road can be considered negligible.

The PM-10 emission factor equation (in

the 5th edition of report AP-42) is a reliable tool for predicting emission rates from

measured winter silt loading. The uncertainty in the predictions is well within the

previously determined reliability of the

equation.
6

J. Kinsey is with Midwest Research Institute, Kansas City, MO 64110-2299.

Charles C. Masser is the EPA Project Officer (see below).

The complete report, entitled “Characterization of PM-10 Emissions from Antiskid

Materials Applied to Ice- and Snow-Covered Roadways—Phase II,” (Order No.

PB95-260402; Cost: $27.00, 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:

Air Pollution Prevention and Control Division

National Risk Management Research Laboratory

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711

• •

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

EPA/600/SR-95/119

Official Business

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