纳米吸湿性串联差分迁移率分析仪的建立与性能评估

Design and characterization of a nano-hygroscopic tandem differential mobility analyzer (nano-HTDMA)

对新生态细粒子(粒径≤30 nm)的吸湿性测量是了解其物化特性,进而深入认识其生成机制及其环境与气候效应的重要手段之一.然而,目前无论是实验室研究还是外场观测都缺乏相应的仪器设备.本文基于商用纳米差分迁移率分析仪(Nano-DMA),设计搭建了一套纳米吸湿性串联差分迁移率分析仪(Nano-HTDMA),开展了系列性能测试,并结合理论模型对该系统进行了评估.对于粒径小于30 nm的纳米气溶胶颗粒的初步测试表明,该装置在室温条件下,加湿范围在相对湿度(RH)20%~90%之间可控,波动范围为±0.5%;并测量了(20±2) nm聚苯乙烯乳胶(PSL)小球在85%相对湿度条件下的吸湿增长因子(g),获得该系统的校准因子为0.007.同时,针对20 nm的硫酸铵和氯化钠气溶胶粒子的吸湿增长进行了测量,与引入形状因子χ后的理论模型进行了分析与对比;并针对不同粒径(15、20、30 nm)的硫酸铵、氯化钠的吸湿增长开展了研究,讨论了粒径对纳米颗粒物g因子、潮解点(DRH)的影响.系列测试结果都表明,不同条件下的实验研究结果与理论模型值都呈现出较好的一致性,证明了该系统的可靠性、稳定性与适用性,有望用于新生态气溶胶粒子的实验室与场地物化特性研究.

To learn the physical and chemical information through measurements of hygroscopicity of the newly formed fine particles(with the diameter less than 30 nm) is pivotal to understand their atmospheric and climate effects. According to the lack of proper commercial tools, a nano-hygroscopic tandem differential mobility analyzer(nano-HTDMA) has been designed and developed. To validate its applicability on the studies of hygroscopicity of fine aerosol particles, a series of characterization and evaluation experiments have been performed, which consist of ①the control of relative humidity(RH) when humidify the particles at room temperature,②the measurement of the correction factor of the system,③the evaluation of shape factor χ on hygroscopic growth factor(g), and ④the evaluation of nanosize effect on g of aerosol particles. Theoretical work based on a model including the Kelvin effect and a size-dependent shape factor has also been performed and discussed. The good agreement between the experimental results and the modeling results validates the applicability of the home-made nano-HTDMA in the future study on hygroscopicity measurements of fine particles in the laboratory as well as in the field.