Characteristics of Metals in Nano/Ultrafine/Fine/Coarse Particles Collected Beside a Heavily Trafficked Road

Abstract

Fine particles emitted from vehicles have adverse health effects because of their sizes and chemical compositions. Therefore, this study attempted to characterize the metals in nano (0.010 < Dp < 0.056 microm), ultrafine (Dp < 0.1 microm), fine (Dp < 2.5 microm), and coarse (2.5 < Dp < 10 microm) particles collected near a busy road using a microorifice uniform deposition impactor (MOUDI) and a Nano-MOUDI. The nano particles were found to contain more of traffic-related metals (Pb, Cd, Cu, Zn, Ba, and Ni) than particles of other sizes, although crustal metals accounted for over 90% of all the particulate metals. Most crustal metals, Ba, Ni, Pb, and Zn in ultrafine particles displayed Aitken modes due to their local origins. The Ag, Cd, Cr, Ni, Pb, Sb, V, and Zn were 37, 50, 28, 30, 24, 64, 38, and 22% by mass, respectively, in < 0.1-microm particles, with submicron mass median diameters (MMDs) in PM(0.01-18) (except Zn) (particularly the < 0.1-microm MMDs for Cd and Sb). These levels raise potential health issues. Particle-bound Zn was more abundant in the accumulation mode than in the nucleation/condensation mode, but the opposite was true for Ag, Cd, and Sb. The Ag, Ba, Cd, Pb, Sb, V, and Zn contents in nano particles were strongly associated with diesel fuel, while the Cu, Mn, and Sr in particles < 0.1 microm were more strongly associated with gasoline. The high content of Si in nano particles, more associated with diesel soot than with gasoline exhaust, is another health concern.