Occurrence of PCDD/Fs in urban air before and after the ban of leaded gasoline.

The source of PCDDs and PCDFs in automotive exhaust is not yet fully explained. The chlorinated hydrocarbons used in the formulation of lead-alkyl additives were suspected as a possible major source. Based on this, the decreasing use of leaded gasoline followed by its final ban (occurred on 1/1/2002, in Italy) should have resulted in a decreasing presence of PCDD/Fs in urban air and possibly some differences in their profile. To investigate these aspects, we monitored PCDD/Fs for one year starting in September 2001, at a medium-traffic road site in Rome, with weekly frequency. Results were then compared with those obtained in a previous study performed before the ban (from February 2000 to January 2001) at the same site. As compared with the previous study, the yearly-averaged overall PCDD/F concentration, as toxic equivalent of 2,3,7,8-TCDD, decreased from 60 to 50 fg m(-3) I-TEQ; it remained unchanged, however, if one sample with a particularly high PCDD/F content was excluded from each data set. The monthly trend confirmed the one found in the former study. On an annual basis, the two mean congener profiles were almost identical. The concentration levels and the constancy of profiles, as calculated for the two periods, do not support the hypothesis of a major role of leaded gasoline, substantially different from unleaded one, in contributing to PCDD/F air pollution.