Measurements of size- and time-resolved elemental concentrations at a California dairy farm

Airborne particulate matter with aerodynamic size less than 10 μm was collected at a California dairy in fall 2006 using a Rotating Drum Impactor (RDI) sampler in 8 size ranges (i.e., 10-5, 5-2.5, 2.5-1.15, 1.15-0.75, 0.75-0.56, 0.56-0.34, 0.34-0.26, and 0.26-0.09 μm). The RDI samples were analyzed using synchrotron X-ray Fluorescence (XRF) at the Advance Light Source (ALS), Lawrence National Berkeley Laboratory, to derive the concentrations of trace elements Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cu, Fe, Mn, and Zn. During this study, periods of rainfall in early November provided an opportunity to isolate particle emission sources. After the rainfalls, elemental concentrations decreased by about 80% for Mg, Al, Si, and Ti, 70% for Fe and Mn, 65% for Cu, and 60% for K and Ca. By contrast, the concentrations of the elements P, S, Zn and Cl did not decrease as significantly as others. Therefore, it is very likely that the dairy drylot corrals could be a major source of the elements Mg, Al, Si, K, Ca, Ti, Cu, Fe, and Mn under dry condition, but not of elements P, S, Zn and Cl. Elements Mg, Al, Si, K, Ca, Ti, Cu, Fe, and Mn were correlated with each other under both dry and wet conditions (R2 ranging from 0.47 to 0.99), indicating that they had common emission sources. Highly correlated sub-groups of elements shifted from dry to wet conditions, R2 > 0.96 among elements Mg, Al, and Si, R2 > 0.93 among elements K, Ca, Ti, Cu, Fe, and Mn under dry condition, and R2 > 0.87 among elements Mg, Al, Si, Ti, Fe, and Mn under wet condition, possibly due to the change in emission sources. Size distribution of the observed elements revealed (1) a general trend that elemental concentrations increased with particle size except for S, which had a peak at 1.15 μm and (2) a greater portion of coarse elements (2.5-10 μm) than fine elements (less than 2.5 μm) for all elements except for S and Zn under both dry and wet conditions.