In Situ Chemical Analysis of the Gas-Aerosol Particle Interface
In Situ Chemical Analysis of the Gas-Aerosol Particle Interface
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DOI：
10.1021/acs.analchem.8b02537
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发表时间：
2018-09-18
影响因子：
7.4
通讯作者：
Rao, Yi
中科院分区：
文献类型：
--
作者：
Qian, Yuqin;Deng, Gang-hua;Rao, Yi
气体-气溶胶颗粒界面被认为有助于大气中二次有机气溶胶的生长。尽管它很重要，但由于缺乏合适的界面特定分析技术，界面的化学组成尚未直接探测。我们早期工作的初步结果表明，随着二次谐波散射（SHS）的发展，在气体-气溶胶颗粒界面上可以直接观察到分子。然而，SHS技术还远远不能成为气体-气溶胶颗粒界面化学成分的分析工具。在这项工作中，我们继续开发了用于气体-气溶胶颗粒界面分子原位化学分析的界面特异性SHS。作为一个例子，我们展示了一种新的SHS探针结晶紫（CV）在气溶胶粒子界面上的相干SHS信号。SHS技术的发展包括：(1)优化了一种更有效的飞秒激光系统，用于从气溶胶颗粒产生SHS。发现飞秒激光的重复频率接近5 MHz是产生SHS的最佳选择；(2)探索更有效的气溶胶粒子SHS探测器。我们发现CCD探测器和单光子计数器对气溶胶粒子的界面SHS信号产生相似的信噪比。CCD探测器是一种更有效的检测SHS的方法，可以大大减少界面响应的采样时间；(3)将优化后的激光系统与CCD探测器相结合，使界面分子的探测灵敏度大大提高了2个数量级以上，有可能探测到单个气溶胶颗粒的界面SHS。这些实验结果不仅为SHS技术提供了深入的分析，而且为进一步发展一种新的气体-气溶胶颗粒界面化学结构的振动和频率散射（SFS）技术奠定了坚实的基础。
The gas-aerosol particle interface is believed to contribute to the growth of secondary organic aerosols in the atmosphere. Despite its importance, the chemical composition of the interface has not been probed directly because of a lack of suitable interface-specific analytical techniques. The preliminary result in our early work has demonstrated direct observations of molecules at the gas-aerosol particle interface with the development of second harmonic scattering (SHS). However, the SHS technique is far away from being an analytical tool of chemical compositions at the gas-aerosol particle interface. In this work, we continued to develop the interface-specific SHS for in situ chemical analysis of molecules at the gas-aerosol particle interface. As an example, we demonstrated coherent SHS signal of a new SHS probe, crystal violet (CV), from interfaces of aerosol particles. The development of the SHS technique includes: (1) Optimization for a more efficient femtosecond laser system in the generation of SHS from aerosol particles. A near 5 MHz repetition rate of a femtosecond laser was found to be optimal for the generation of SHS; (2) exploration of a more effective detector for SHS of aerosol particles. We found that both a CCD detector and a single-photon counter produce similar signal-to-noise ratios of the interfacial SHS signals from aerosol particles. The CCD detector is a more effective option for the detection of SHS and could greatly reduce sampling time of the interfacial responses; (3) combination of the optimal laser system with the CCD detector, which has greatly improved the detection sensitivity of interfacial molecules by more than 2 orders of magnitude and could potentially detect interfacial SHS from a single aerosol particle. These experimental results not only provided a thorough analysis of the SHS technique but also built a solid foundation for further development of a new vibrational sum frequency scattering (SFS) technique for chemical structures at the gas-aerosol particle interface.