Size-differentiated source profiles for fugitive dust in the Chinese Loess Plateau

Size-differentiated fugitive dust chemical source profiles are determined for the Chinese Loess Plateau, a major source of Asian dust. Fifteen loess samples at five sites (Yulin, Yanchi, Huanxian, Luochuan, and Xi’an) were collected, dried, sieved, resuspended, and sampled through TSP, PM10, PM2.5, and PM1 inlets onto filters for analysis of 40 major and trace elements (Na to U), six ions (Cl−, NO3−, SO42−, Na+, K+, and NH4+), organic carbon (OC) and elemental carbon (EC), and carbonate carbon (CO3-C). The abundances of major species (>1%) include Al, Si, K, Ca, Fe, OC and CO3-C, in four size-differentiated source profiles. OC accounted for ∼90% of total carbon in four size fractions for most of the profiles. Enrichment factors indicated that the 18 elements (Na, Mg, Si, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Y, Zr, Ba) found in the samples were dominated by crustal sources. Enrichment factors for Co, As, Se, Mo, Cd, In, Sb, and Tl are one to two orders of magnitude larger than crustal-derived elements, suggesting the influence of anthropogenic pollution sources. Compared with loess samples, V, Cr, Ni, Cu, Zn, Sb, SO42−, and NO3− are enriched in ambient PM2.5 aerosol samples, implying that Asian dust contains pollution components in downwind regions of the desert. The elemental ratios of Si, K, Ca, Ti, Mn, and Fe to Al in Asian dust source regions compared well with those found at downwind regions such as Korea, Japan, and the North Pacific. These ratios can be used as fingerprints to trace the transport path of Asian dust.