In situ emission levels of polynuclear aromatic hydrocarbons from gasoline and diesel engine vehicles on an expressway

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Abstract
Aerosol samples were collected in the Tsuburano Tunnel on Tomei Expressway during a week to evaluate the in‐situ emission levels of polynuclear aromatic hydrocarbons (PAHs) in the exhaust gas from a diesel engine car and a gasoline engine car. The atmospheric levels of PAHs indicated a significant variation with the traffic density of the passing vehicles in the tunnel. Particularly, the correlation coefficients between the traffic density and the PAHs levels were statistically higher for the gasoline car traffic than that for the diesel car traffic with confidence levels of 99 %. On the other hand, the contribution of PAH per vehicle to the tunnel atmosphere decreased with the increase of the ratio of the fraction of diesel car traffic relative to the total traffic. On the basis of these results, an experimental equation was derived with respect to a mass balance of PAH in the tunnel. As a result, it was estimated that on a mass basis, the average emission rates (μg/hr) of pyrene, chrysene, benz(a)anthracene, perylene, benzo(a)pyrene, and benzo(ghi)perylene from diesel engine vehicles were 4.2×103, 5.4×102, 3.6×102, 3.4×10, 1.0×102, and 1.3×102, respectively.