Passive samplers have proven to be effective for continuous monitoring of volatile organic compounds (VOCs) in ambient air in remote, urban and industrial environments. Thermal desorption tubes fitted with endcaps that facilitate passive uptake through diffusion are now routinely used for monitoring fugitive benzene emissions from refineries and petrochemical facilities across North America (EPA Method 325A/B). However, deployment periods of 14 days are typically employed to minimize the risk of poor retention, requiring 26 deployments per year to return an annual average concentration for comparison with chronic exposure health-based standards. Here, we explore extending the deployment duration of these passive samplers to one, two and three months by limiting VOC uptake rates using an alternative diffusive endcap featuring a smaller cross-sectional area. Field testing was performed beside a major highway during two separate three-month campaigns. Uptake rates for benzene, toluene, ethylbenzene and xylenes (BTEX) were observed to remain linear for deployments of up to three months when using the low-uptake endcaps. Application of the low-uptake endcaps and the uptake rates determined here will enable annual average concentrations of BTEX to be calculated using only four tube deployments per year. The cost savings associated with this decreased deployment frequency will facilitate increased spatial resolution during future exposure assessment studies. The stability of selected air toxics within the tubes was also assessed and the results suggest that while aromatic VOCs are stable for storage times of at least 70 days, chloroform and trichloroethylene begin to degrade within two weeks of sampling.

被动采样器已被证明可有效地连续监测偏远、城市和工业环境中环境空气中的挥发性有机化合物 (VOC)。装有端盖的热解吸管通过扩散促进被动吸收，现在通常用于监测北美炼油厂和石化设施的逸散苯排放（EPA 方法 325A/B）。但是，通常采用 14 天的部署期来最大程度地降低保留不良的风险，每年需要 26 次部署才能返回年平均浓度，以便与基于慢性暴露健康的标准进行比较。在这里，我们探索将这些被动采样器的部署持续时间延长到一个，通过使用具有较小横截面积的替代扩散端盖来限制 VOC 吸收率，可以缩短两到三个月的时间。在两个独立的三个月活动期间，在一条主要公路旁进行了现场测试。当使用低吸收端盖时，观察到苯、甲苯、乙苯和二甲苯 (BTEX) 的吸收率在长达三个月的部署中保持线性。应用低吸收端帽和此处确定的吸收率将使每年仅使用四个管部署来计算 BTEX 的年平均浓度。与这种降低部署频率相关的成本节约将有助于在未来的暴露评估研究中提高空间分辨率。