NONMETHANE EXHAUST COMPOSITION IN THE SYDNEY HARBOR TUNNEL - A FOCUS ON BENZENE AND 1,3-BUTADIENE

The concentrations of individual hydrocarbon species in the Sydney Har bour Tunnel were measured and used to estimate the average composition of emissions from moving motor vehicles in the Sydney urban area. The mean composition of non-methane hydrocarbons in the tunnel air on a w eight basis was relatively constant. The mean concentrations for benze ne and 1,3-butadiene were 45 and 13 ppbv, respectively, which in turn represented similar to 5.2% w/w and similar to 1.0% w/w of the total n on-methane C-2-C-10 hydrocarbons in the tunnel air. The unit risk fact or and the maximum incremental reactivity factor for 1,3-butadiene are approximately 30 times higher and 25 times higher, respectively, than the corresponding values for benzene. The concentration (mu gm(-3)) o f benzene, however, is only about 5 times that of 1,3-butadiene. On th is basis, the relative contribution to the risk associated with exposu re to fresh motor vehicle emissions in Sydney would be about 6 times h igher for 1,3-butadiene than for benzene. Similarly, the contribution made by 1,3-butadiene to the total hydrocarbon reactivity of the tunne l air will be about 5 times that of benzene. Samples of three differen t grades of petrol (leaded, unleaded and premium unleaded) from three different brands of fuel were also analysed on two separate occasions. Compositions of leaded and standard unleaded petrol averaged across t he three different brands are quite similar. The average aromatic cont ent (% w/w) of the 3 different commercial brands were similar to 35 an d 30% for leaded and unleaded petrol, respectively. However, premium u nleaded petrol has a much higher aromatic content of similar to 47% w/ w. Comparison of the petrol and tunnel compositions demonstrated that benzene is enriched relative to other aromatics in exhaust compared to its proportion in the petrol. (C) 1996 Elsevier Science Ltd