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Method 102 Revisio*n 1 Procedure for the Sampling and Analysis of Atmospheric Benzene Method 102 Introduction 1.1 This procedure describes a method of sampling and analyzing atmospheric concentrations of benzene in the range of 0.5 to 1000 parts per billion (ppb). 1.2 Lower concentrations may be analyzed by increasing the sample volume and using a cryogenic trap to concentrate the sample. 1.3 Higher concentrations may be analyzed by direct injection of a sample into a sample loop of a gas chromatograph. 2 Method 2.1 Air is sampled into a Tedlar (polyvinyl fluoride) bag at a constant rate (30 to 40 mL/min) during selected time intervals by means of an automatic sampler. 2.2 After sampling, the ambient air bag sample is returned to the laboratory for analysis. 2.3 The sample is introduced into the gas chromatograph (GC) sample stream by means of gas injection valves and ana- lyzed by a photoionization detector. 2.4 The GC data system quantitates benzene by integrating the peak area and calculating the concentration from factors determined during calibration with standards. 3 tkpQ�rat qs 3.1 The sampler system consists of a diaphragm pump with a by-pass flow constrictor, a solenoid valve, a flow meter with a flow control. valve, pressure regulator, fittings, and tubing to convey air samples to the Teflon bag. The entire assembly, including a 7-dky timer and associated electrical circuitry to control the filling of the sample bags, is compactly mounted on a metal chassis and operates on a 110 VAC power supply. 3.2 Tedlar bags, 2 mil thickness, 50 liter capacity, equipped with stainless steel quick disconnect fittings are used to contain the sample. The bags are prepared in conformity with the ARB docurrie.nt,"Procedure for Fabrication and Testing of Sample Bags", (see Appendix B). For sampling, the bags are placed in rigid opaque containers to protect their contents from the sunlight.