Closure between Semi-continuous Measurement of PM2.5 Mass and Composition
The USEPA is promoting the development and application of sampling methods for the semi-continuous determination of PM2.5 mass and chemical composition. Data obtained with these methods will significantly improve our understanding of the primary sources, chemical conversion processes and meteorological atmospheric processes which lead to observed PM2.5 concentrations and will aid in the understanding of the origin of PM2.5 effects. A major challenge in this effort is the development of methods which accurately measure both the nonvolatile and semi-volatile (nitrate and organic material) fraction of PM2.5. The closure between semi-continuous measurement of PM2.5 mass and the estimation of PM2.5 mass from the semi-continuous measurement of fine particulate constituents has been evaluated in Riverside, CA in July-August 2005 and in Lindon, UT in January-February 2007. Emphasis was on the use of instruments which should accurately determine the semi-volatile organic material and ammonium nitrate in fine particles. Instruments used in the studies included the FDMS TEOM and the GRIMM monitor (to measure PM2.5 mass, including the semi-volatile nitrate and organic material), a conventional TEOM monitor, a newly developed dual oven Sunset Laboratory ambient carbon monitor (to measure EC and both nonvolatile and semi-volatile carbonaceous material), an Aethalometer (to measure BC) and a prototype Dionex GP-IC (to measure nitrate and sulfate). The semi-continuous data were validated with PC-BOSS integrated measurements. This paper will report on the successful attempts to quantitatively measure both mass and all the major species of PM2.5, including the semi-volatile material, on a semi-continuous basis.