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Facility Fence-Line Monitoring Using Passive Samplers

ABSTRACT In 2009, the U.S. Environmental Protection Agency (EPA) executed a year-long field study at a refinery in Corpus Christi, TX, to evaluate the use of passive diffusive sampling technology for assessing time-averaged benzene concentrations at the facility fence line. The purpose of the study was to investigate the implementation viability and performance of this type of monitoring in a real-world setting as part of EPA's fence-line measurement research program. The study utilized 14-day, time-integrated Carbopack X samplers deployed at 18 locations on the fence line and at two nearby air monitoring sites equipped with automated gas chromatographs. The average fence-line benzene concentration during the study was 1075 parts per trillion by volume (pptv) with a standard deviation of 1935 pptv. For a 6-month period during which wind direction was uniform, the mean concentration value for a group of downwind sites exceeded the mean value of a similar upwind group by 1710 pptv. Mean value differences for these groups were not statistically significant for the remaining 6-month time period when wind directions were mixed. The passive sampling approach exhibited acceptable performance with a data completeness value of 97.1% (n = 579). Benzene concentration comparisons with automated gas chromatographs yielded an r 2 value of 0.86 and a slope of 0.90 (n = 50). A linear regression of duplicate pairs yielded an r 2 of 0.97, unity slope, and zero intercept (n = 56). In addition to descriptions of technique performance and general results, time-series analyses are described, providing insight into the utility of 2-week sampling for source apportionment under differing meteorological conditions. The limitations of the approach and recommendations for future measurement method development work are also discussed. IMPLICATIONS Improved knowledge of air pollution concentrations at industrial facility fence lines is a topic of increasing environmental importance. Fence-line and process monitoring can yield many benefits, ranging from enhanced risk management to cost savings through improved process control. Efforts are underway within EPA to develop and test various cost-effective fence-line monitoring strategies for potential use in a range of research and regulatory applications. Among these, passive diffusive sampling is emerging as a promising technique for time-integrated fence-line monitoring applications.