单颗粒气溶胶质谱仪串联热稀释器在线测量单个气溶胶颗粒的挥发性

摘要

Volatility can influence the lifetime of particles in the atmosphere, and provide useful information on the formation of secondary aerosol. The previous studies generally utilized thermodenuder ( TD ) to investigate the volatility behavior of particles. Using TD, semivolatile species are vaporized at different temperature, and the vaporized gas is adsorpted by activated charcoal. However, carbon might be emitted from activated charcoal under high temperature or activated charcoal ageing. In this study, a new method was developed for the measurement of particle volatility by coupling a thermodiluter system to an online single particle aerosol mass spectrometer ( SPAMS) . Aerosol particles were passed into two different channels, and then analyzed by SPAMS. Through Channel 1, aerosol particles were heated to different temperature by heating tube, then non-volatile particles and volatile gas entered into the diluter. After diluting and cooling by diluent air, the non-volatile particles were analyzed by SPAMS. Through Channel 2, aerosol particles were analyzed directly by SPAMS without the heating process. Particle volatility was obtained by comparing the information ( particle size, particle number and mass spectrum ) of particles through Channels 1 and 2. Laboratory tests showed that the diluter could avoid the re-condensation of volatiles to the particles. This developed method was applied in the real time measurement of individual particle volatility in the spring of Guangzhou. The results showed that these particles were primarily comprised of highly volatile and moderate volatile species.%颗粒挥发性可以影响颗粒在大气中的寿命,对大气颗粒物中二次气溶胶的形成机制研究有一定的参考价值。以往研究测量颗粒挥发性采用的是热熔蚀器,其活性炭吸附器一旦老化后,在较高温度下可能会释放出活性炭,造成测量失真。本研究针对热熔蚀器的上述缺点,以稀释器替代活性炭吸附器部分,与单颗粒气溶胶质谱仪( SPAMS)连接,建立了一种在线分析单个气溶胶颗粒挥发性的测量方法。气溶胶颗粒分别通过两个通道进入SPAMS分析颗粒信息。通道1,气溶胶颗粒由管路进入加热器,被加热至不同的温度,颗粒挥发产生的气体和挥发后的颗粒内核进入稀释器部分,利用干净干燥冷的稀释气对加热挥发后的气体和颗粒进行稀释,使颗粒温度降低并短时间内不与气体发生冷凝,最后进入SPAMS进行检测。通道2为单独硅胶管,其长度与通道1相同,气溶胶颗粒通过通道2直接进入SPAMS检测。通过对比通道1和通道2获得的颗粒信息(粒径、数目和质谱信息等),得到气溶胶颗粒在不同温度下的挥发性。实验室用标准物质进行评估测试,结果表明,采用稀释器可以避免活性炭吸附器使用时间变长而失效,防止挥发性物质冷凝回到颗粒中。应用本方法初步测定了广州市春季气溶胶的挥发性,表明春季气溶胶多为高度挥发性和中度挥发性物质。