Mobile sources of atmospheric polycyclic aromatic hydrocarbons in a roadway tunnel

Abstract

Amounts of polycyclic aromatic hydrocarbons (PAHs) and oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in samples collected from the air, from the dust on a guardrail, and from the soils on a tunnel roadway at five sampling sites in a regular roadway tunnel were chemically analyzed in order to determine their sources. Among the 23 PAHs found in the air samples, pyrene was found in the highest concentration (43±7.2 ng/m³), followed by fluoranthene (26±4.3 ng/m³). Among 20 oxy-PAHs found in the air samples, anthraquinone was found in the greatest amount (56±3.9 ng/m³). The average concentration of the major PAHs found in the guardrail dust samples were 6.9±0.77 μg/g for pyrene, 5.5±0.76 μg/g for fluoranthene, and 2.6±0.30 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the guardrail dust samples were 9.2±3.5 μg/g for anthraquinone and 1.4±0.50 μg/g for 2-methylanthraquinone. The average concentration of the major PAHs found in the soil samples were 1.1±0.31 μg/g for fluoranthene, 0.92±0.21 μg/g for pyrene, and 0.72±0.16 μg/g for phenanthrene. The average concentration of the major oxy-PAHs found in the soil samples were 1.2±0.88 μg/g for anthraquinone, 0.18±0.04 μg/g for 4-biphenylcarboxaldehyde, and 0.13±0.08 μg/g for 2-methylanthraquinone. The BeP ratios calculated from the results suggest that most PAHs found in the samples collected from the roadway tunnel were from automobile exhaust gases.

Introduction

The number of automobiles in Japan was 0.534 per capita in 1995. Japan ranks fourth after the US, Canada, and Australia, and about the same as England, France, and Germany (Japan Ministry of Finance, 1997). The number of automobiles registered and their mileage have been increasing consistently and continuously. The number of diesel cars has also increased significantly after the oil shortage in 1974; 6.5% and 19% of the total number of cars in 1970 and 1995, respectively. Air pollution in a metropolitan area is probably caused by chemicals exhausted from automobiles (Black et al., 1980; EPA, 1980; Lee and Lewis, 1980).

Exhaust gases from diesel cars contain diesel emission particulates (DEP) which are associated with diseases such as cancer, asthma, and hay fever (IARC, 1983). Automobile exhaust gases contain many non-polar polycyclic aromatic hydrocarbons (PAHs) such as benzo[a]pyrene (BaP) and benzo[e]pyrene (BeP), and also oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) such as anthraquinone and xanthone. PAHs and oxy-PAHs are generally formed from oil and coal upon incomplete combustion. They are deposited naturally or anthropogenically into the environment. Since PAHs are one of the most serious pollutants because of their carcinogenicity and mutagenicity (IARC, 1983), it is important to determine the amounts of PAHs and oxy-PAHs from mobile sources in the air in order to investigate possible adverse effects caused by air pollution in metropolitan cities. If stationary sources, such as power plants and home heating systems contribute PAHs contamination equally in areas of big cities, different concentrations of PAHs between a heavily traveled roadway and a city park comes from mobile sources, such as exhaust from automobiles (Nielsen, 1996; Lim et al., 1999).

In order to determine the sources of PAHs contamination in the environment, samples of PAHs in the dust taken from the electrostatic precipitator of a sintering furnace and in the soot particles taken from the inner surfaces of vehicle tailpipes were compared with the standard reference sample of diesel particulate matter (SRM 1650). Samples of PAHs in the dust collected from the ventilator on the ceiling of a laboratory and airborne particulate collected in a rural area were compared with the standard reference sample of urban dust (SRM 1649) (Oda and Itikawa, 1992; Oda et al., 1998a).

Tunnels have received much attention from environmental scientists as an area heavily exposed to automobile exhaust gases. Many researchers used highway tunnels to obtain pollution data from diesel and gasoline cars. In the present study, amounts of PAHs and oxy-PAHs in the samples collected from the air, from the dust on a guardrail, and from the soils of a roadway in a regular roadway tunnel were measured to assess the amounts of environmental pollution caused by automobile exhausts in the tunnel.