Characterization and quantitative analysis of asphalt fumes generated in asphalt pavement materials

Abstract

Asphalt fumes are generated during the producing or heating of asphalt binders or products containing asphalt binders. It has been proved that asphalt fumes have adverse effects on human health, such as the irritation of eyes and respiratory tracts and potentially carcinogenic risk. The hazardous compounds in asphalt fumes have been extensively studied to evaluate the toxicity of asphalt fumes. However, too little attention has been paid to the accuracy and efficiency of methods for the characterization of these hazardous compounds. Issues and uncertainties in the methods may lead to inconsistent measurement results and cause biased toxicity assessment of asphalt fumes. In this study, multiple fractions of lab-produced and field-produced asphalt fumes were examined, including total particulate matter (TPM), organic matter, and polycyclic aromatic hydrocarbons (PAHs). The total particulate matter and organic matter in the aerosol phase of asphalt fumes were determined gravimetrically. The organic matter in the vapor phase of asphalt fumes and PAHs in asphalt fumes were analyzed using various chromatographic methods, including solid phase extraction (SPE), matrix solid-phase dispersion (MSPD), semi-preparative high-performance liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS). Furthermore, this study evaluated the effects of solvents, clean-up treatments, and matrix compounds on the accurate characterization of asphalt fumes. The extraction efficiency of different solvents was analyzed using a series of statistical methods: analysis of variance (ANOVA), Dunnett method, and multiple comparisons with the best (MCB). In order to evaluate the matrix effect in asphalt fumes, deuterated PAHs were used to calculate the matrix factor. In analyzing PAHs in asphalt fumes, the external standard calibration method, the standard addition calibration (SAC) method, and the internal standard calibration (ISC) method were systematically compared and evaluated. The major outcomes of the study are summarized as follows. 1) Solvents with high efficiency and low toxicity in extracting the organic matter in asphalt fumes were identified. Four solvents (acetone, hexane, dichloromethane, and acetonitrile) are comparable to benzene in extracting organic matter from the total particulate matter of asphalt fumes, and acetone and hexane are recommended to replace benzene, which is a commonly used hazardous solvent. 2) In extracting PAHs, acetone and dichloromethane provide the highest recovery of total PAHs from asphalt fumes, and dichloromethane is particularly better at recovering high-molecular-weight PAHs. 3) The matrix compounds of asphalt fumes exhibit a prominent enhancement effect on the analytical response of PAHs, and the matrix effect can be decreased but not eliminated by performing clean-up treatments. Hence, quantification of PAHs in asphalt fumes would be biased without considering the matrix effect. 4) Compared to the external standard calibration method, the internal standard calibration method and the standard addition calibration method can provide more reliable results of PAHs in asphalt fumes. 5) Styrene-butadiene-styrene (SBS) as a modifier in asphalt binders cannot inhibit the release of asphalt fumes, and crumb rubber significantly increases the concentration of asphalt fumes and PAHs therein. 6) Paver driver has the highest exposure risk to PAHs during pavement construction, followed by screedmen and rakers. The present study enhances our understanding of the chemical compositions of asphalt fumes generated from different pavement materials. Moreover, these findings and developed methods contribute to the characterization of asphalt fumes in several aspects. 1) Analysts and health professionals now have cleaner, more accurate, and more effective methods when analyzing asphalt fumes. 2) This is the first study that finds, reports, and corrects the matrix effect in characterizing PAHs in asphalt fumes—an issue that causes serious analysis bias. 3) The quantification methods developed in this study provide a solid foundation for future studies on asphalt fumes.