Reactive semivolatile contaminants, such as isocyanates, can be particularly difficult to assess in occupational environments. While standard methods exist for isocyanates, there are still significant differences between the results they provide for various occupational environments or processes. This study presents the validation of a laboratory system for the generation of controlled atmospheres of isocyanates. A system consisting of different modules generated airborne methylene diphenyl diisocyanate (MDI) by nebulizing a solution into mixing and exposure chambers with control of flow rate, temperature, and relative humidity. Sampling was performed through an eight-port flow splitter that allowed only very slight within-test variability. MDI was measured using the Asset EZ4-NCO® and a modified version of the Iso-Chek® sampling system. MDI specific particle-size distribution was measured by a Marple Sierra cascade. Aerosol real-time monitoring was performed using a condensation particle counter, an electrical low-pressure impactor (ELPI+), and an aerosol optical spectrometer, providing additional information on system stability and particle-size distribution of the generated aerosol. The system was able to generate MDI concentration levels ranging from 4 to 233 μg m⁻³, with a steady-state level reached within 5 minutes, and with well-documented intra-test and inter-test variability (RSD of 4% and 15%, respectively). Accuracy and representativeness of MDI data were confirmed by the agreement between MAMA and Asset EZ4-NCO (used as reference), with a mean bias of 3%. Using the Asset EZ4-NCO capability, the vapor-particle partitioning of MDI was evaluated to be 8% and 92%, respectively, at a concentration ranging from 20 to 25 μg m⁻³. The system may therefore be used for exhaustive method intercomparison studies and could also be adapted to generate other emission types of semivolatile compounds.

中文翻译：

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适应性气雾化亚甲基二苯基二异氰酸酯生成系统的开发和表征

反应性半挥发性污染物，如异氰酸酯，在职业环境中特别难以评估。虽然存在异氰酸酯的标准方法，但它们为各种职业环境或过程提供的结果之间仍然存在显着差异。本研究展示了用于生成异氰酸酯受控气氛的实验室系统的验证。由不同模块组成的系统通过将溶液雾化到混合和暴露室中并控制流速、温度和相对湿度来生成空气中的二苯基甲烷二异氰酸酯 (MDI)。采样是通过一个八端口分流器进行的，该分流器仅允许非常轻微的测试内变异。MDI 是使用 Asset EZ4-NCO® 和改进版的 Iso-Chek® 采样系统测量的。MDI 特定的粒度分布通过 Marple Sierra 级联测量。气溶胶实时监测使用冷凝粒子计数器、电子低压冲击器 (ELPI+) 和气溶胶光谱仪进行，提供有关系统稳定性和生成的气溶胶粒度分布的额外信息。该系统能够产生 4 到 233 μg m 的 MDI 浓度水平^-3，在 5 分钟内达到稳态水平，并且具有充分记录的测试内和测试间变异性（RSD 分别为 4% 和 15%）。MDI 数据的准确性和代表性由 MAMA 和 Asset EZ4-NCO（用作参考）之间的协议确认，平均偏差为 3%。使用 Asset EZ4-NCO 功能，MDI 的蒸气-颗粒分配分别评估为 8% 和 92%，浓度范围为 20 至 25 μg m ^-3。因此，该系统可用于详尽的方法比对研究，也可用于生成其他排放类型的半挥发性化合物。