United States Air and Energy Engineering

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

C.C. Lutes, R.J. Thomas, and R. Burnette

E AP Project Summary

Evaluation of Emissions

From Paving Asphalts

Research and Development EPA/600/SR-94/135 November 1994

This work provides data from pilotscale 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 maintained for several hours near the highest temperature likely to be encountered in a real paving operation (176°

C). Although concentration levels observed 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. Volatile organic compound (VOC) analyses

showed significant amounts of benzene

emitted from both types of asphalt studied. 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 concentrations observed, though significant,

were close to the limit of detection.

Statistically significant emissions of

both total particulates and PM10 were

found from both types of asphalt hotmix 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 documented in a separate report of the same

title (see Project Report ordering information at back).

Introduction

Paving asphalt is a widely used product

with incompletely characterized emissions

to the atmosphere. Approximately 20 million tonnes of asphalt were sold in 1976.

Asphalt is most often used in paving applications as a “hot-mix” of petroleum-derived 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 dibenzothiophene, methyldibenzothiophene, phenanthrene, 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). Concentrations were also reported for the following organic species (μg/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
2

a lack of emissions data for specific pollutants measured in such a way that emissions from asphalt paving could be estimated.

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 quantitative data on the emissions of specific pollutants from paving asphalt. In addition,

because paving asphalts with recycled

crumb rubber additives are beginning to

be used (The Intermodal Surface Transportation Efficiency Act requires the use

of rubber additives), this project also compared the emissions of asphalt with and

without this additive. The acquired data

are intended to provide insight into the

possible health effects of human exposure 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 quantitatively characterize organic and inorganic

emissions from the asphalt paving processes. Although it was recognized that

asphalt experiences a variety of temperature 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 measurement 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 operation, was used to provide a realistic basis

for the estimation of emissions from an

asphalt process. Samples of paving asphalts provided to EPA by asphalt vendors were heated in a specially designed

stainless steel vessel within the Open

Burning Simulation Test Facility (see Figures 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

Sample Shed

Sampling Controls

Particulate PAH Analyzer

Heated Sample Line

CEMs

O2 SO2

CO2

THC

NO CO

Hazardous Air

Pollutants Mobile

Laboratory

Data Acquisition

System

Insulated

Sample

Duct

Asphalt

Heating

Vessel +

Platform

Burn Hut

Tedlar

Bags

Metals

PM10 Head

Organics

PM10 Head

Tedlar Bags Train Inlets +

Semivolatile/XAD-2 Train Inlet

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 monoxide (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 Figure 1). The organic constituents were analyzed both qualitatively and quantitatively

using gas chromatograph/mass spectrometer (GC/MS), the lead was quantified using a graphite furnace atomic adsorption

method (GFAA). Hydrogen sulfide was

measured using a colorimetric Dräger tube

methodology.

The concentration data for all analytes

were converted to emission rates expressed 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 concentration of analyte, the surface area of the

asphalt heating vessel, and the duration

of the sampling period.

Figure 1. Aerial view of the products of incomplete combustion facility.
3

Results and Conclusions

Successful triplicate tests were conducted of an AC10 asphalt hot-mix material, of an AC10 asphalt hot-mix material

with a rubber additive, and of a facility

blank test condition. Though concentration levels were, in most cases, near the

detection limits of the analytical methods

applied, statistically significant emissions

of a variety of pollutant species were observed (data summarized in Tables 1 and

2).

VOC analyses showed statistically significant amounts of benzene emitted from

both types of asphalt studied. None of the

other 55 volatile compounds targeted for

quantitative analysis were observed in statistically significant concentrations. A wide

variety of volatile compounds, not specifically targeted for quantitative analysis,

were also seen in various samples although no consistent set of compounds

could be established.

Analysis of vapor-phase semivolatile

species showed statistically significant concentrations of 2-methylphenol from the

AC10 with rubber tests and significant

emissions of diethyl phthalate from both

hot-mix materials. Observations of phthalate emissions should be treated with extreme caution because phthalates are notorious as analytical artifacts because they

are present in a very wide variety of plastic materials.

None of the other semivolatile species

targeted showed statistically significant

emissions in the vapor-phase analyses.

Analysis of particulate-phase semivolatile species by full scan mass spectrometry showed statistically significant concentrations 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 observed at concentrations near the detection limit in the full scan mass spectrometry analyses and analytical interferences

from hydrocarbon coeluters were suspected, an additional analysis of semivolatile particulate-phase samples was

conducted by a more sensitive selected

ion monitoring method. This analysis targeted 16 PAH species of primary interest

to the project and revealed statistically

significant emissions of 7 of the 16 species 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 emissions of both total particulates and PM10

were found from both types of asphalt

hot-mix material tested.

The estimated emission values measured in this work could be combined with

appropriate fate and transport data to

model the exposure of populations (either

occupational or general) to pollutants generated in the asphalt paving process. To

facilitate such a modeling effort, the emissions 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,

however, recall the limitations of this pilotscale 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 exposure scenarios will vary widely.

Although some statistically significant differences were found between the emissions from the asphalt materials tested

with and without rubber, these differences

were not in general dramatic. In addition,

although the emissions for some pollutants, 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 asphalt hot-mixes does not have a dramatic

impact on the air emissions generated in

the paving process.

Stack (Sealed)

Sample Duct

Tedlar Liner

Aluminum

Tedlar Wrapping

Platform

Deflector

Shield

60.3 cm

15.25 cm

Heater

Air Inlet

Air Inlet

(Sealed +

Inoperable)

Figure 2. Diagram of the burn hut as configured for the asphal heating tests; some sampling

equipment not shown for clarity.
4

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

Indeno(1,2,3-cd)Pyrene

Lead

PM10 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 1. List of Compounds with Statistically Significant Results

AC10 without rubber vs. AC10 with rubber vs.

facility blank facility blank

Level of Estimated emissions Level of Estimated emissions

Compound significance (μg/(m2*min) significance* μg/(m2*min)

Benzene 0.002 ≤ 57 0.002 ≤ 110

2-Methyl Phenol NS ≤ 7.2 0.05 ≤ 23.7

Diethyl Phthalate 0.10 ≤ 32.7 0.10 ≤ 34.37

Bis(2-ethylhexyl)phthalate NS ≤ 5.1 0.10 ≤ 5.3

Naphthalene 0.10 ≤ 0.103 NS ≤ 0.063

Fluoranthene 0.10 ≤ 1.648 0.10 ≤ 1.178

Pyrene 0.10 ≤ 1.469 0.10 ≤ 1.612

Benzo(a)anthracene NS ≤ 0.786 0.10 ≤ 0.653

Chrysene 0.02 ≤ 4.420 0.05 ≤ 1.957

Benzo(k)fluoranthene 0.01 ≤ 1.106 NS ≤ 0.306

Benzo(a)pyrene 0.05 ≤ 0.660 0.10 ≤ 0.204

Indeno(1,2,3-c,d)pyrene 0.05 ≤ 0.141 NS ≤ 0.065

Lead 0.05 ≤ 0.542 NS ≤ 1.10

PM10 Particulate (organic train) 0.05 26,850 0.05 12,710

Total Particulate

(organic XAD-2 train) 0.05 27,700 0.05 12,950

PM10 Particulate (metals train) 0.05 37,710 0.10 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).

Table 2. Summary of Levels of Significance and Estimated Emission Values
5

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

EPA/600/SR-94/135

Official Business

Penalty for Private Use $300

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35