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 ϭ 579). Benzene concentration comparisons with automated gas chromatographs yielded an r 2 value of 0.86 and a slope of 0.90 (n ϭ 50). A linear regression of duplicate pairs yielded an r 2 of 0.97, unity slope, and zero intercept (n ϭ 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.

Passive air sampling for nitrogen dioxide (NO(2)) and select volatile organic compounds (VOCs) was conducted at 24 fire stations and a compliance monitoring site in Dallas, Texas, USA during summer 2006 and winter 2008. This ambient air monitoring network was established to assess intra-urban gradients of air pollutants to evaluate the impact of traffic and urban emissions on air quality. Ambient air monitoring and GIS data from spatially representative fire station sites were collected to assess spatial variability. Pairwise comparisons were conducted on the ambient data from the selected sites based on city section. These weeklong samples yielded NO(2) and benzene levels that were generally higher during the winter than the summer. With respect to the location within the city, the central section of Dallas was generally higher for NO(2) and benzene than north and south. Land use regression (LUR) results revealed spatial gradients in NO(2) and selected VOCs in the central and some northern areas. The process used to select spatially representative sites for air sampling and the results of analyses of coarse- and fine-scale spatial variability of air pollutants on a seasonal basis provide insights to guide future ambient air exposure studies in assessing intra-urban gradients and traffic impacts.

In the summer of 2003, ambient air concentrations of volatile organic compounds (VOCs) were measured at 12 sites within a 3-km radius in Deer Park, Texas near Houston. The purpose of the study was to assess local spatial influence of traffic and other urban sources and was part of a larger investigation of VOC spatial and temporal heterogeneity influences in selected areas of Houston. Seventy 2-h samples were collected using passive organic vapor monitors. Most measurements of 13 VOC species were greater than the method detection limits. Samplers were located at 10 residential sites, a regulatory air monitoring station, and a site located at the centroid of the census tract in which the regulatory station was located. For residential sites, sampler placement locations (e. g., covered porch vs. house eaves) had no effect on concentration with the exception of methyl tertiary-butyl ether (MTBE). Relatively high correlations (Pearson r > 0.8) were found between toluene, ethylbenzene, and o,m,p-xylenes suggesting petroleum-related influence. Chloroform was not correlated with these species or benzene (Pearson r < 0.35) suggesting a different source influence, possibly from process-related activities. As shown in other spatial studies, wind direction relative to source location had an effect on VOC concentrations.

The Houston-Galveston metropolitan area has a relatively high density of point and mobile sources of air toxics, and determining and understanding the relationship between emissions and ambient air concentrations of air toxics is important for evaluating potential impacts on public health and formulating effective regulatory policies to control this impact, both in this region and elsewhere. However, conventional ambient air monitoring approaches are limited with regard to expense, siting limitations, and representative sampling necessary for adequate exposure assessment. The overall goal of this multiphase study is to evaluate the use of simple passive air samplers to determine temporal and spatial variability of the ambient air concentrations of selected volatile organic compounds (VOCs) in urban areas. Phase 1 of this study, reported here, was a field evaluation of 3M organic vapor monitors (OVMs) involving limited comparisons with commonly used active sampling methods, an assessment of sampler precision, a determination of optimal sampling duration, and an investigation of the utility of a simple modification of the commercial sampler. The results indicated that a sampling duration of 72 hr exhibited generally low bias relative to automated continuous gas chromatography measurements, good overall precision, and an acceptable number of measurements above detection limits. The modified sampler showed good correlation with the commercial sampler, with higher sampling rates, although lower than expected.

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