United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-94/135 November 1994
EPA Project Summary
Evaluation of Emissions
From Paving Asphalts
C.C. Lutes, R.J. Thomas, and R. Burnette
This work provides data from pilot-
scale measurements of the emissions
of specific air pollutants from paving
asphalt both with and without recycled
crumb rubber additives. The methods
used in this work measured emissions
from a static layer of asphalt main-
tained for several hours near the high-
est temperature likely to be encoun-
tered in a real paving operation (176°
C). Although concentration levels ob-
served for most species were in most
cases near the detection limits of the
analytical methods applied, statistically
significant emissions of a variety of
pollutant species were observed. Vola-
tile organic compound (VOC) analyses
showed significant amounts of benzene
emitted from both types of asphalt stud-
ied. An analysis targeting 16 polycyclic
aromatic hydrocarbons (PAHs) species
of primary interest revealed significant
emissions of 7 of the 16 species when
the AC10 asphalt without rubber tests
were compared to the facility blank
tests. The emissions of 5 of 16 PAH
species were significantly higher in the
AC10 thin layer with rubber tests than
in the facility blank tests. The concen-
trations observed, though significant,
were close to the limit of detection.
Statistically significant emissions of
both total participates and PM10 were
found from both types of asphalt hot-
mix material tested.
This Project Summary was developed
by EPA's Air and Energy Engineering
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 infor-
mation at back).
Introduction
Paving asphalt is a widely used product
with incompletely characterized emissions
to the atmosphere. Approximately 20 mil-
lion tonnes of asphalt were sold in 1976.
Asphalt is most often used in paving ap-
plications as a "hot-mix" of petroleum-de-
rived asphalt and aggregate material
(crushed stone or gravel).
Typical elemental analyses of asphalt
show the following approximate weight
percentages: carbon, 80-90%; hydrogen,
5-11%; sulfur, 0.4-7.3%; nitrogen, 0.4-
0.9%; and oxygen, 0.0-2.0%. Among the
compounds identified in a soxhlet extract
of an asphalt sample were dibenzothio-
phene, methyldibenzothiophene, phenan-
threne, pyrene, and fluoranthene.
A previous study attempted to measure
pollutant levels in the emissions, known
as "blue smoke," from an asphalt hot-mix
facility using a temporary enclosure to aid
sampling. Concentrations measured (in
ppm, vol) were methane (2-3 ppmv), C2-
C6 hydrocarbons (< 1 ppmv), hydrogen
sulfide (< 0.2-1.5 ppmv), sulfur dioxide (< 2
ppmv), carbon monoxide (3-6 ppmv), and
nitrogen dioxide (0.05-0.08 ppmv). Con-
centrations were also reported for the fol-
lowing organic species (|ig/1,000 m3):
pyrene (44-240), benzo(a)anthracene (5-
38), benzo(a)pyrene (3-22), benzo-
(e)pyrene (non-detectable -40), perylene
(5-16). The particulate matter (PM) was
determined to be composed of paraffins
(28%), cycloparaffins (40%), aromatics
(26%), and sulfur aromatics (6%). An
evaluation of available literature shows
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Insulated
Sample
Duct
Sample Shed
Sampling Controls
Particulate PAH Analyzer
Tedlar
Bags
Metals
PM10 Head
Organics
PM10 Head
Tedlar Bags Train Inlets +
Semivolatile/XAD-2 Train Inlet
Burn Hut
Hazardous Air
Pollutants Mobile
Laboratory
X
Heated Sample Line
OEMs
[ THC | [ SO2
[ CO2 i [ NO [ [ CO \
\Data Acquisition
• System
Figure 1. Aerial view of the products of incomplete combustion facility.
V
a lack of emissions data for specific pol-
lutants measured in such a way that emis-
sions from asphalt paving could be esti-
mated.
The objective of this work, conducted
through the guidance of an EPA-approved
Quality Assurance (QA) Test Plan (AEERL
QA Category II), was to provide quantita-
tive data on the emissions of specific pol-
lutants from paving asphalt. In addition,
because paving asphalts with recycled
crumb rubber additives are beginning to
be used (The Intermodal Surface Trans-
portation Efficiency Act requires the use
of rubber additives), this project also com-
pared the emissions of asphalt with and
without this additive. The acquired data
are intended to provide insight into the
possible health effects of human expo-
sure to asphalt emissions as well as to
help assess the contribution of asphalt
emissions to ozone non-attainment. This
report also provides baseline data to which
emissions from other modified asphalt
products can be compared.
Approach
The project consisted of a replicate study
to collect and qualitatively and quantita-
tively characterize organic and inorganic
emissions from the asphalt paving pro-
cesses. Although it was recognized that
asphalt experiences a variety of tempera-
ture conditions and physical disturbances
during a paving process, the investigators
believed that it was impractical to simulate
this temperature profile or agitation in a
small-scale test. Therefore, a measure-
ment of emissions from a static layer of
asphalt, maintained for a period of several
hours near the highest temperature likely
to be encountered in a real paving opera-
tion, was used to provide a realistic basis
for the estimation of emissions from an
asphalt process. Samples of paving as-
phalts provided to EPA by asphalt ven-
dors were heated in a specially designed
stainless steel vessel within the Open
Burning Simulation Test Facility (see Fig-
ures 1 and 2). Testing included two types
of asphalt—an AC10 grade asphalt hot
mix and an AC10 grade asphalt hot mix
with a crumb rubber additive.
Air sampling was conducted within the
facility through medium volume PM10 heads
for semivolatile organics and particulate
phase lead. Samples of volatile organics
were removed directly from the facility and
collected in Tedlar bags. A portion of the
air within the facility was diverted to an
adjacent sampling facility via an induced
draft duct. A portion of the sample from
the induced draft duct was also monitored
for carbon dioxide (CO2), carbon monox-
ide (CO), nitric oxide (NO), oxygen (O2),
sulfur dioxide (SO2), particulate-bound
polycyclic aromatic hydrocarbons (PAH),
and total hydrocarbons (THC) by a series
of continuous emission monitors (see Fig-
ure 1). The organic constituents were ana-
lyzed both qualitatively and quantitatively
using gas chromatograph/mass spectrom-
eter (GC/MS), the lead was quantified us-
ing a graphite furnace atomic adsorption
method (GFAA). Hydrogen sulfide was
measured using a colorimetric Dragertube
methodology.
The concentration data for all analytes
were converted to emission rates ex-
pressed on a per time and per surface
area basis. These rates were calculated
from the volumes sampled by each train,
the volumes of air flowing into the test
facility, the measured mass or concentra-
tion of analyte, the surface area of the
asphalt heating vessel, and the duration
of the sampling period.
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Results and Conclusions
Successful triplicate tests were con-
ducted of an AC10 asphalt hot-mix mate-
rial, of an AC10 asphalt hot-mix material
with a rubber additive, and of a facility
blank test condition. Though concentra-
tion levels were, in most cases, near the
detection limits of the analytical methods
applied, statistically significant emissions
of a variety of pollutant species were ob-
served (data summarized in Tables 1 and
2).
VOC analyses showed statistically sig-
nificant amounts of benzene emitted from
both types of asphalt studied. None of the
other 55 volatile compounds targeted for
quantitative analysis were observed in sta-
tistically significant concentrations. A wide
variety of volatile compounds, not specifi-
cally targeted for quantitative analysis,
were also seen in various samples al-
though no consistent set of compounds
could be established.
Analysis of vapor-phase semivolatile
species showed statistically significant con-
centrations of 2-methylphenol from the
AC10 with rubber tests and significant
emissions of diethyl phthalate from both
hot-mix materials. Observations of phtha-
late emissions should be treated with ex-
treme caution because phthalates are no-
torious as analytical artifacts because they
are present in a very wide variety of plas-
tic materials.
None of the other semivolatile species
targeted showed statistically significant
emissions in the vapor-phase analyses.
Analysis of particulate-phase semivola-
tile species by full scan mass spectrom-
etry showed statistically significant con-
centrations of bis(2-ethylhexyl)phthalate.
To reiterate, observations of phthalate
emissions should be treated with extreme
caution because phthalates are notorious
as analytical artifacts and are present in a
very wide variety of plastic materials. None
of the other semivolatile species targeted
showed statistically significant emissions
in the PM analyses.
Because some PAH species were ob-
served at concentrations near the detec-
tion limit in the full scan mass spectrom-
etry analyses and analytical interferences
from hydrocarbon coeluters were sus-
pected, an additional analysis of semi-
volatile particulate-phase samples was
conducted by a more sensitive selected
ion monitoring method. This analysis tar-
geted 16 PAH species of primary interest
to the project and revealed statistically
significant emissions of 7 of the 16 spe-
cies when the AC10 thin layer without
rubber tests were compared to the facility
blank tests. The emissions of 5 of 16 PAH
species were significantly higher in the
AC10 thin layer with rubber tests than in
the facility blank tests. The emissions of
two species were significantly higher in
the tests without the rubber additive than
in the tests with the additive.
No statistically significant emissions of
hydrogen sulfide were found in these tests.
A very low level of lead may have been
emitted in the AC10 thin layer without
rubber tests. Statistically, significant emis-
sions of both total particulates and PM10
were found from both types of asphalt
hot-mix material tested.
The estimated emission values mea-
sured in this work could be combined with
appropriate fate and transport data to
model the exposure of populations (either
occupational or general) to pollutants gen-
erated in the asphalt paving process. To
facilitate such a modeling effort, the emis-
sions results have been presented as a
function of asphalt surface area so that
emissions from the paving of an area of
road could be estimated based on the
road length and width. Modelers should,
Heater
Air Inlet
however, recall the limitations of this pilot-
scale study, especially those discussed in
Section 3.1 of the full report. The facility
air concentrations reported in this work
should not be used directly to evaluate
risk to exposed populations because ex-
posure scenarios will vary widely.
Although some statistically significant dif-
ferences were found between the emis-
sions from the asphalt materials tested
with and without rubber, these differences
were not in general dramatic. In addition,
although the emissions for some pollut-
ants, such as benzene, were significantly
higher in the rubber-containing asphalt,
the emissions of other pollutants, such as
benzo(k)fluoranthene, were higher in the
non-rubber-containing asphalt. Therefore,
the data gathered in these experiments
indicate that the addition of rubber to as-
phalt hot-mixes does not have a dramatic
impact on the air emissions generated in
the paving process.
Stack (Sealed)
Tedlar Liner
Aluminum
Tedlar Wrapping
60.3 cm
Air Inlet
(Sealed +
Inoperable)
Platform
Figure 2. Diagram of the burn hut as configured for the asphal heating tests; some sampling
equipment not shown for clarity.
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Table 1. List of Compounds with Statistically Significant Results
Compounds for which AC10 without rubber emissions were significantly higher than the facility
blank emissions:
Benzene
Diethyl Phthalate
Napthalene
Fluoranthene
Pyrene
Chrysene
Benzo(k)fluoranthene
Benzo(a)pyrene
lndeno(1,2,3-cd)Pyrene
Lead
PMW Particulate (as measured on both trains)
Total Particulate
Compounds for which AC10 with rubber emissions were significantly higher than the facility
blank emissions:
Benzene
2-Methyl Phenol
Diethyl Phthalate
bis(2-Ethylhexyl)phthalate
Fluoranthene
Pyrene
Benzo(a)pyrene
PM10 Particulate (as measured on both trains)
Total Particulate
Compounds for which AC10 without rubber emissions were significantly higher than AC10 with
rubber emissions:
Benzo(k)fluoranthene
Benzo(a)pyrene
Compounds for which AC10 with rubber were significantly higher than AC10 without rubber
emissions:
Benzene
m,p-Xylene
2-Methyl Phenol
Table 2. Summary of Levels of Significance and Estimated Emission Values
AC 10 without rubber vs.
facility blank
AC 10 with rubber vs.
facility blank
Compound
Benzene
2-Methyl Phenol
Diethyl Phthalate
Bis(2-ethylhexyl)phthalate
Naphthalene
Fluoranthene
Pyrene
Benzo(a)anthracene
Chrysene
Benzo(k)fluoranthene
Benzo(a)pyrene
lndeno(1 ,2, 3-c, d)pyrene
Lead
PMW Particulate (organic train)
Total Particulate
(organic XAD-2 train)
PMW Particulate (metals train)
Level of
significance
0.002
NS
0.10
NS
0.10
0.10
0.10
NS
0.02
0.01
0.05
0.05
0.05
0.05
0.05
0.05
Estimated emissions
(lj.g/(m2*min)
<57
<7.2
<32.7
<5.1
< 0.1 03
< 1.648
< 1.469
< 0.786
< 4.420
< 1.106
< 0.660
< 0.1 41
< 0.542
26,850
27,700
37,710
Level of
significance*
0.002
0.05
0.10
0.10
NS
0.10
0.10
0.10
0.05
NS
0.10
NS
NS
0.05
0.05
0.10
Estimated emissions
Hg/(m2*min)
<110
<23.7
< 34.37
<5.3
< 0.063
< 1.178
< 1.612
< 0.653
< 1.957
< 0.306
< 0.204
< 0.065
<1.10
12,710
12,950
19,810
NS Not statistically significant at >90% confidence level.
* Level of significance is defined as the probability of making a type 1 error (i.e., of falsely rejecting the tested
hypothesis, in this case the tested hypothesis is that the means are equal).
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C. Lutes, R. Thomas, and R. Burnette are with Acurex Environmental Corp.,
P.O. Box 13109, Research Triangle Park, NC 27709.
Bobby E. Daniel is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Emissions from Paving Asphalts,"
(Order No. PB95-129110/AS: Cost: $36.50; 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
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-94/135
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