Fine-particle Mn and other metals linked to the introduction of MMT into gasoline in Sydney, Australia： Results of a natural experiment

PM2.5 particulates were analyzed using accelerator-based ion beam methods for a suite of 21 species （H, C, Na, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Pb） to evaluate the contribution to Sydney air associated with the introduction of MMT as a replacement for Pb. MMT was discontinued in 2004. Teflon filters continuously sampled for 7 years from 1998 to 2004 were analyzed from two sites： a suburb （Mascot） close to the Central Business District CBD （n=718）] and a high trafficked area, and a relatively rural （background） setting, ～20 km west of the CBD （n=730）. Mean Mn concentrations in air at the background site increased from 1.5- 1.6 ng/m^3 to 〈2 ng/m^3 at the time of the greatest MMT use whereas those at Mascot increased from about 2 to 5 ng/m^3. From the maximum values, the Mn showed a steady decrease at both sites concomitant with the decreasing use of MMT. Lead concentrations in air at both sites decreased from 1998 onwards, concomitant with the phase out of leaded gasoline in 2002. A high correlation was obtained for the relationship between Mn in air and lead replacement gasoline （LRG） use （R2 0.83） and an improved correlation for Mn/Al＋Si＋K and LRG use （R2 0.93）. With Mn concentrations normalized to background values of Al＋Si＋K to account for the lithogenically-derived Mn, the proportion of anthropogenic Mn was -70%. Changes for Mn and Pb in the particulates are attributed to the before-during-after use of MMT and decreasing use of Pb in gasoline.