Performance evaluation of modified Semi-continuous Elements in Aerosol Sampler-III

A field study was conducted to evaluate the performance of a Semi-continuous Elements in Aerosol Sampler-III (SEAS-III), designed to collect ambient PM2.5 aerosol samples at a time resolution of 30 min for elemental concentration measurements. Two identical but modified SEAS-III samplers were operated for four continuous weeks in Dearborn, MI, during July–August 2007. A total of 2308 samples were collected from the two samplers. Sampling completeness from the primary and duplicate samplers was 90% and 84%, respectively. All of the collected samples were analyzed for dilute acid-extractable trace metal concentrations using HR-ICPMS. l of 878 collection time-matched sample pairs were available to evaluate whole-system uncertainty from collocated concentration measurements. The collocated precision for the 27 studied elements (Al, As, Ba, Ca, Cd, Ce, Cs, Cu, Fe, Ge, K, La, Mg, Mn, Mo, Na, P, Pb, Rb, S, Sb, Se, Sn, Sr, Ti, V, and Zn) varied between 9% and 40%. Twenty elements showed precision better than 25%. Uncertainty estimates from propagation of errors compared well with the whole-system uncertainty values for all minor aerosol elements studied. SEAS-III measurements of As, Cd, Ge, K, La, Mn, Mo, Na, Rb, Se, Sb, Sr, Ti, V, and Zn correlated well (r > 0.8) with a FRM equivalent PM2.5 integrated filter sampling method. Based on these measurements, collection efficiency of SEAS-III was estimated to be 87 ± 16%. Solubility of particles in the collection medium (water) was identified as a possible reason for low recovery of Al, Fe, Pb, Sb, and Sn.