MANGANESE AND OTHER TRACE-ELEMENTS IN URBAN SNOW NEAR AN EXPRESSWAY

The Mn contamination arising from the combustion of MMT (methylcyclope ntadienyl manganese tricarbonyl) in unleaded gasoline was assessed usi ng snow collected at different distances 15, 25, 125 and 150 m from an expressway (Montreal, Canada) in February 1993. The snow samples were analyzed by atomic absorption and by neutron activation for total Mn, Mg, Cu, V, Al, Zn, Fe, Na, and Ca concentrations in the soluble (< 0. 4 mu m) and particulate fractions. ANOVA with ranked values was perfor med to compare element concentrations and soluble/particulate particul ate ratios among receptor sites and depths. Principal component analys is was used to describe the spatiotemporal variations of the depositio n rates and the influence of meteorological factors. The average conce ntration of all trace elements, except Mg, Cu, and V, decreased signif icantly (p < 0.05) from receptor sites near the road (15-25 m) to thos e farther away (125-150 m). The deposition rates of all metals and ion s, except Cu, were highly positively correlated (tau = 0.5-0.9) with e ach other and inversely correlated with snowfalls. Wind frequency show ed no correlation with deposition rate. The spatial trend was similar for all these elements making it difficult to distinguish Mn arising f rom the combustion of MMT from that due to other sources, such as road dust. Only the soluble/particulate ratio calculated for Mn seemed hig her than that for the other metals, which might be explained by the pa rticle size of Mn from MMT (0.2-0.4 mu m). The present study only indi cates a direct contamination of the snow by road activities and substa ntial deposition of trace elements near the roadway; no clear link can be established between motor vehicle emissions and the concentration of Mn in snow. Copyright (C) 1996 Elsevier Science Ltd.