PAHs pollution in air of arterial roads was investigated from October 1998 to October 2001 in Hangzhou, China. The results showed that ∑10 PAHs was 13-36 μg/m3 , among which, BaP, a strong carcinogenic kind ranged from 0.034 μg/m3 to 0. 12 μg/m3 . PAHs pollutions in four seasons were winter ＞ autumn ＞ spring-summer. The annual averages of ∑PAHs concentration were 25 μg/m3 for 1999, 28μg/m3 for 2000, and 29 μg/m3 for 2001, respectively. Leaded gasoline was banned in December 1998 in Hangzhou, thus comparative measurements with PAHs in leaded and lead-free gasoline powered motor exhausts made it certain that the use of lead-free gasoline leaded to a heavier PAHs pollution in roadside air from December, 1998, in China, and ∑PAHs in air samples after the lead-banning were more than twice of that in samples before the action. For the large contribution of vehicle discharge to air pollution in roadside, further research was performed to suggest the factors influencing PAHs distribution in vehicle exhaust in order to control air pollution effectively.Compared to gasoline engines, emissions from diesel engines were less toxic, although they might produce more PAHs. Of the same vehicular and oil type, automobiles of longer mileages produced more toxic PAHs. PAHs distributions in the vehicular exhausts were related to the oil type. Large difference was found in the abundance of 3-, 5- and 6-ring PAHs between exhausts from gasoline and diesel oil engines. Diesel oil engines produced relative lighter PAHs such as NAPH, ACEN, FLUOR, while gasoline engines emitted heavier kinds such as BkF, IN and BP. The automobile produced more PAHs with the increase of mileage especially FLUR, PY, BaP, BP. Some significant ratios for traffic source in Hangzhou such as PHEN/AN, FLUR/PY, IN/BP were 0.50-4.3, 0.58-7.4, 0.51-1.5,respectively. A source fingerprint for vehicle exhausts of a mixture of vehicle and oil types in the city district for light-duty vehicle was the abundance of BaA, followed by NAPH, BP, IN. 4-ring PAHs such as FLUR, PY, BaA and CHRY were the most predominant kindsfollowed by 6-ring PAHs(BP, IN).