T-FTIR研究大气颗粒物表面非均相反应

Heterogeneous Reactions on the Surface of Atmospheric Particles:A Transmission FTIR Spectroscopy Study

大气颗粒物表面发生的非均相反应已成为目前大气科学领域的研究热点。由于现有的研究手段存在很多不足,目前人们对大气中痕量气体物质在颗粒物表面非均相反应动力学和机理了解得还很有限。文章开发了基于透射傅里叶变换红外光谱(T-FTIR)的研究颗粒物表面反应的方法,可以从分子水平观测颗粒物表面的物理化学变化。通过对一个大气模型反应体系即常温常压下甲基丙烯醛(MAC)在二氧化硅颗粒物表面反应的表征,验证了该方法可以有效地定性和定量表征颗粒物上的非均相反应过程。研究结果显示,反应过程的红外谱图信号清晰,表征灵敏;红外光能量较低,不会损害样品,可以实现对反应的原位观测。经HPLC分析结果证明,T-FTIR表征结果的重现性和准确性好,即使在湿度存在条件下其定性和定量也是可靠的。该方法为实验室模拟研究实际大气条件下的非均相反应提供了一种有效手段。

Heterogeneous reactions of trace gases on the surface of particles in the atmosphere play a important role in the key atmospheric processes, and have been of increasingly interest in atmospheric sciences. However, these reactions, especially the corresponding detailed kinetics and mechanisms, have not been well understood, due to the deficiencies in the current experimental methods. The authors developed a novel experimental method for the study of heterogeneous reactions, based on transmission FTIR spectroscopy （T-FTIR）, providing an understanding of the detailed physical chemistry that occurs on the surface of particles at the molecular level. In this method, the particles were evenly coated on a metal grid, and the gaseous reactant and the infrared beam were introduced to pass through the grid in the reactor. This method was used to explore the heterogeneous reaction of methacrolein （MAC） on the surface of SiO2 particles, a model heterogeneous reaction, under simulated atmospheric conditions. The result demonstrated that T-FTIR is an applicable and powerful technique for the qualitative and quantitative analysis of such a heterogeneous reaction, due to its excellent spectral signal. In addition, the particle sample will not be scathed due to the low energy of infrared light, thus the in situ investigation of the reaction on particles could be carried out. Compared with the HPLC analysis results, the repeatability and accuracy of the qualitative and quantitative analysis of T-FTIR have proven satisfactory, even though the reactions ran in the humid air. The authors＇ method can provide an effective tool for the laboratory simulation of heterogeneous reactions under the atmospheric conditions.