Size distribution and sources of trace metals in ultrafine/fine/coarse airborne particles in the atmosphere of Shanghai

Airborne particulate matter (PM) samples in 13 different size-fractions from 0.0283 to 9.92 mu m were collected in winter of 2007 at three sites in Shanghai, China. The PM exhibited a bimodal distribution with a major mode in the fine particle size range (D-p = 0.2-1 mu m) and a minor mode in the coarse range (D-p = 1-10 mu m), suggesting that fine particle pollution is dominant in the Shanghai atmosphere. Trace metals in PM exhibited the following distribution patterns: (1) unimodal distribution in the fine fraction (Pb, Cd, Se, Sn, Bi, and Zn), (2) unimodal distribution in the coarse fraction (Mg, Al, Fe, Ca, Ba, Sr, Ge, Zr, U, and rare earth elements), (3) bimodal distribution, with one mode in the fine fraction and one in the coarse fraction (Cu, Mn, K, Ga, V, Rb, and Cs), and (4) multimodal distribution (Na, Ti, Cr, Co, As, Ni, Mo, Ag, W, Pt, Au, S, and Cl) throughout the entire aerosol size spectrum. In addition to these size distributions, Aitken modes due to local origins were also evident for Se, Sn, Cu, V, Ti, Cr, Co, As, Ag, Mo, and Pt, whose respective mass in the ultrafine particles (<0.1 mu m) was 10, 23, 13, 19, 23, 14, 67, 32, 79, 40, and 21%, with submicron mass median aerodynamic diameters (MMADs) in PM0.02-9.92 (except Pt). In particular, the MMADs for Co and Ag were <0.1 mu m, which increase potential health issues. The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, coal combustion, and the steel industry.