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The U.S. Environmental Protection Agency is promoting the development and application of sampling methods for the semicontinuous determination of fine particulate matter (PM 2.5 , particles with an aerodynamic diameter Ͻ2.5 m) mass and chemical composition. Data obtained with these methods will significantly improve the understanding of the primary sources, chemical conversion processes, and meteorological atmospheric processes that lead to observed PM 2.5 concentrations and will aid in the understanding of the etiology of PM 2.5 -related health effects. During January and February 2007, several semicontinuous particulate matter (PM) monitoring systems were compared at the Utah State Lindon Air Quality Sampling site. Semicontinuous monitors included instruments to measure total PM 2.5 mass (filter dynamic measurement system [FDMS] tapered element oscillating microbalance [TEOM], GRIMM), nonvolatile PM 2.5 mass (TEOM), sulfate and nitrate (two PM 2.5 and one PM 10 [PM with an aerodynamic diameter Ͻ10 m] ionchromatographic-based samplers), and black carbon (aethalometer). PM 10 semicontinuous mass measurements were made with GRIMM and TEOM instruments. These measurements were all made on a 1-hr average basis. Source apportionment analysis indicated that sources impacting the site were mainly urban sources and included mobile sources (gasoline and diesel) and residential burning of wood, with some elevated concentrations because of the effect of winter inversions. The FDMS TEOM and GRIMM instruments were in good agreement, but TEOM monitor measurements were low because of the presence of significant semi-volatile material. Semi-volatile mass was present dominantly in the PM 2.5 mass.

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