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The objectives of this paper are to contrast the relative variability of replicate laboratory measurements of selected chemical components of fine particulate matter (PM) with total variability from collocated measurements and to compare the magnitudes of the uncertainties determined from collocated sampler data with those

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Consumer products are potentially significant sources of volatile organic compounds (VOCs), which are precursors to the formation of ozone in photochemical smog. To address the problem of ozone formation in ambient air, the U.S. Environmental Protection Agency (EPA) has been involved in the development of test methods for measuring the VOC content of consumer products. This paper describes results of an interlaboratory study to estimate the repeatability (precision of analyses performed by a single laboratory) and reproducibility (precision of analyses performed by different laboratories) of the consumer products' VOC measurement method based on EPA Method 24 (for VOCs in surface coatings).The mean method repeatability was 2.7 wt % VOC, and the mean method reproducibility was 4.8 wt % VOC. Method repeatability ranged from 0.2 to 4.4 wt % VOC, and reproducibility ranged from 0.6 to 11.9 weight percent VOC. The precision of the VOC method for consumer products is similar to the precision of EPA Method 24 for surface coatings.

A test method based upon the adsorption of chloroform onto charcoal was evaluated for the collection and analysis of chloroform emissions from stationary sources. In this method, a source gas sample is pulled through adsorption tubes containing activated charcoal (to adsorb the chloroform), and chloroform is extracted from the charcoal with a hexane/methanol mixture. The extract is analyzed by gas chromatography with an electron capture detector. Procedures in Environmental Protection Agency (EPA) Method 301 were utilized to test the suitability of the method under field conditions at two sampling sites (paper mills). EPA Method 301 requires that four separate trains ("quad train") operate simultaneously in each run. During each run, two of the four sampling trains were spiked with a known amount of gaseous chloroform. The quad train sampling was performed six or more times. In the first field test, the stack emissions of chloroform were approximately 300 ppm, the mean spike recovery was 82%, the precision of the method for unspiked samples was within 5%, and the sampling bias was -43 ppm. Modifications were made to the sampling method and the spike gas introduction system. The revised method was then tested at a second field site which had chloroform emissions of approximately 220 ppm. The mean spike recovery improved to 95%, the unspiked sample precision was within 5%, and the sampling bias improved to -8.5 ppm.