Diffusive sampling of a mixture of 42 volatile organic compounds (VOCs) in humidified, purified air onto the solid adsorbent Carbopack X was evaluated under controlled laboratory conditions. The evaluation included variations in sample air temperature, relative humidity and ozone concentration. Linearity of samples with loading was examined both for a constant concentration with time varied up to 24 h and for different concentrations over 24 h. Reverse diffusion and its increase with accumulation of sample were determined for all compounds. Tubes were examined for blank levels, change of blanks with storage time, and variability of blanks. Method detection limits were determined based on seven replicate samples. Based on this evaluation, 27 VOCs were selected for quantitative monitoring in the concentration range from approximately 0.1 to 4 ppbv. Comparison results of active and diffusive samples taken over 24 h and under the same simulated ambient conditions at a constant 2 ppbv were interpreted to estimate the effective diffusive sampling rates (ml min(-1)) and their uncertainties and to calculate the corresponding diffusive uptake rates (ng ppmv(-1) min(-1)).

An automated gas chromatographic (autoGC) system was used to collect and analyze both nonpolar and polar volatile organic compounds (VOCs) in ambient air. This system combines the use of dual multiadsorbent traps to provide continuous air sampling for 57 min of each hour; a dry helium purge to remove extraneous gases, including some residual water vapor retained in the sorbent packing; thermal desorption of analytes onto a VOC-focusing trap cooled by a small Stirling-cycle refrigerator; and GC/mass spectrometric detection using ion trap technology. Cleanliness, linearity, method detection limits (MDLs), precision, and accuracy of the autoGC were determined for 41 VOCs. For most of the compounds tested, MDLs were less than 0.10 ppbv, response was linear over the 1-40 ppbv range, accuracy was (20%, and trap-to-trap precision was (20%. Linear response for a set of polar VOCs was also determined over the 5-50 ppbv range. The autoGC was successfully operated in a mobile laboratory at a field site in Axis, AL, for 10 days, during which time the system was in operation 24 h/day with minimal interruptions. This autoGC is designed for monitoring subsets of the 97 VOCs among the 189 hazardous organic compounds that are listed in Title III of the Clean Air Act Amendments of 1990.

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This study evaluates performance of nitrogen dioxide (NO2) and volatile organic compound (VOC) passive samplers with corresponding reference monitors at two sites in the Detroit, Michigan area during the summer of 2005. Ogawa passive NO2 samplers and custom-made, re-useable Perkin-Elmer (PE) tubes with Carbopack X sorbent for VOCs were deployed under week-long sampling periods for six weeks. Precise results (5% relative standard deviation, RSD) were found for NO2 measurements from collocated Ogawa samplers. Reproducibility was also good for duplicate PE tubes for benzene, toluene, ethylbenzene, and xylene isomers (BTEX species, all < or = 6% RSD). As seen in previous studies, comparison of Ogawa NO2 samplers with reference chemiluminescence measurements suggested good agreement. Generally good agreement was also found between the PE tubes and reference methods for BTEX species.