Similarities and differences in PM10 chemical source profiles for geological dust from the San Joaquin Valley, California

A systematic sampling and analysis approach was followed to acquire chemical source profiles for six types of geological dust in California’s San Joaquin Valley. Forty-seven samples from 37 locations included: (1) urban and rural paved roads, (2) residential and agricultural unpaved roads and parking areas, (3) almond, cotton, grape, safflower, and tomato fields, (4) dairy and feedlot surfaces, (5) salt-laden lake and irrigation canal drainage deposits, and (6) building and roadway construction/earthmoving soil. These samples were dried, sieved, resuspended, sampled through a PM10 inlet onto filters, and chemically analyzed to construct PM10 source profiles (fractional mass abundances and uncertainties) for 40 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Y, Zr, Mo, Pd, Ag, Cd, In, Sn, Sb, Ba, La, Au, Hg, Tl, Pb, and U), 7 ions (Cl � ,N O 3 ,P O 4� ,S O 4� ,N a + ,K + , and NH4 ), organic and elemental carbon (OC and EC), 8 carbon fractions (OC1, OC2, OC3, OC4, OP, EC1, EC2, and EC3), and carbonate carbon. Individual source profiles with analytical precisions were averaged and compared to quantify differences in chemical abundances for: (1) duplicate laboratory resuspension sampling, (2) multiple sampling within the same agricultural field, (3) sampling at different locations for the same land-use activity, (4) sampling of different activities regardless of location, and (5) grouping of different activities into generalized emission inventory source categories. Distinguishing features were found among composite source profiles of six source types. Elemental carbon and Pb marked paved road dust; Na + , Na, S, and SO4� marked salt deposits; OC, PO4� ,P , K + , K, and Ca characterized animal husbandry; and several metals (Ti, V, Mn) marked construction soil, with abundances 2–10 times higher than those of other profiles. High-sensitivity X-ray fluorescence analysis resulted in detectable alkali and rare earth elements. Ga, Zr, Sn, and Ba were found in some of the paved road dust profiles; toxic species such as As, Mo, Cd, Sb, and U were found in salt deposits from canal drainage; and Pd, Rb, Sr, and Tl were found in construction dust. The profile-compositing methodology can be used for evaluating similarities and differences for other source characterization studies. r 2003 Elsevier Science Ltd. All rights reserved.