Performance Audit Results Using EPA Method 25 During Source Compliance Tests

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Abstract
The U.S. Environmental Protection Agency (EPA) has recently promulgated a revised Method 25, "Determination of Total Gaseous Nonmethane Organic Emissions as Carbon", for volatile organic compound emissions from stationary sources. The method currently requires an analysis of a set of two audit samples concurrently with any compliance source test samples and in exactly the same manner to evaluate the sample collection and subsequent analysis technique. EPA has established a Method 25 audit material repository that is available to federal, state, and local agencies or their contractors for use in performance audits during source compliance testing. Two types of audit approaches for EPA Method 25 have been developed. The first approach uses commercially available gas cylinders containing known concentrations of selected volatile organics and carbon dioxide in an inert balance gas of nitrogen. A second approach involves the use of a stainless steel cartridge containing a solid sorbent (Tenax) spiked with known quantities of selected organic compounds that can be used to generate organic vapors quantitatively using thermal desorption. The organics released from either a cylinder or cartridge were collected and analyzed using Method 25 procedures. Studies were also performed to determine the precision, accuracy, stability, and feasibility of using both the materials in performance audits. Results indicate that both types of audit materials are stable and useful in conducting Method 25 audits. Subsequent to completion of the stability studies, 50 performance audits using gas cylinders have been conducted to assess the accuracy of Method 25 procedures during or prior to source compliance testing at surface coating operations. These audit results generally were within .+-. 20 percent of the audit concentrations.

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