Manganese and other trace elements in urban snow near an expressway Original

The Mn contamination arising from the combustion of MMT (methylcyclopentadienyl manganese tricarbonyl) in unleaded gasoline was assessed using 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 μm) and particulate fractions. ANOVA with ranked values was performed to compare element concentrations and soluble/particulate ratios among receptor sites and depths. Principal component analysis was used to describe the spatiotemporal variations of the deposition rates and the influence of meteorological factors. The average concentration of all trace elements, except Mg, Cu, and V, decreased significantly (p < 0.05) from receptor sites near the road (15–25 m) to those farther away (125–150 m). The deposition rates of all metals and ions, except Cu, were highly positively correlated (τ = 0.5–0.9) with each other and inversely correlated with snowfalls. Wind frequency showed no correlation with deposition rate. The spatial trend was similar for all these elements making it difficult to distinguish Mn arising from the combustion of MMT from that due to other sources, such as road dust. Only the soluble/particulate ratio calculated for Mn seemed higher than that for the other metals, which might be explained by the particle size of Mn from MMT (0.2–0.4 μm). The present study only indicates a direct contamination of the snow by road activities and substantial deposition of trace elements near the roadway; no clear link can be established between motor vehicle emissions and the concentration of Mn in snow.