Size distributions of trace elements associated with ambient particular matter in the affinity of a major highway in the New Jersey-New York metropolitan area

To characterize the size distributions of trace elements associated with particulate matter in the areas heavily impacted by traffics, eleven sets of size-segregated aerosol samples were collected using a MOUDI sampler in winter and summer of 2007-2008 along the side of a highway in the northeast New Jersey near New York City. Selected trace metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, Sc, V and Zn) in aerosol samples were determined by ICPMS. A bimodal mass size distribution with peaks at the size ranges of 0.32-0.56 μm and 3.2-5.6 μm was identified, and the general size distributions of the mass concentrations did not change significantly with seasons. Trace metals of potential anthropogenic origin, including Cd, Co, Fe, Ni, Pb, Sb and Zn, had higher concentrations and enrichment levels in winter, especially for fine particles. For trace metals of crustal origin, such as Al and Sc, their size distributions of enrichment factors showed significant seasonal variations, while no such variations were found for Cd, Co, Cr, Ni, Pb, Sb, V, and Zn. Two groups of size distributions in trace metal concentrations were identified using cluster analysis: (1) coarse particles (>1.0 μm) with accumulation of mainly crustal trace metals such as Al, Fe, Sc, and Mn; (2) fine particles (<1.0 μm) with accumulations of trace metals of anthropogenic origins such as Cd, Pb, Ni, V and Co. The size distributions of trace metal enrichment factors showed primarily monotonic decline patterns with overwhelmingly high peaks in the size range of 0.18-0.32 μm for most of the trace metals from pollution sources. Crustal elements including Cu (summer), Mn (summer) and Sc (winter), however, showed tilted normal distributions pattern with peaks at 1.0-1.8 μm. Three major types of sources for these metals were identified at this location: (1) brake wear and fuel combustion, (2) primary fuel combustion, and (3) tires abrasion and fuel combustion. The particulate trace metals in the study area are primarily characterized by either the mixed sources or the exhaust emissions source. Weather factors, in particular temperature, wind speed and precipitation, were found to significantly (α = 0.05) influence the concentrations of trace metals and their size distributions.