Heterogeneous reactions on the surface of atmospheric particles: A transmission FTIR spectroscopy study

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 (MC) 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.