Effect of bolide impacts on Earth's surface environment Analysis of chemical reactions within a giant vapor plume

点击翻译按钮获取中文摘要

In this research project we conducted a series of laser ablation experiments simulating the thermodynamic state in the vapor loud induced by K/T impact event in order to understand the basic chemical processes involved in SO_x reactions. We constructed a new laser irradiation system with a X-Y stage to ensure that each laser pulse can ablate fresh target (CaSO4) surface. Also we incorporated a new high-performance quadruple mass spectrometer to enhance the signal-to-noise ratio of our mass measurements. Furthermore, we used a high power Nd:YAG Laser (15J/pulse) to generate a large high-temperature plumes. Combining this laser facility with the existing small Nd:YAG laser, we could cover more than 10^3 of dynamic range of laser energy. This allows us to obtain a very reliable data on SO_x reactions. Finally, we conducted high-speed spectroscopic measurements of laser-induced vapor plumes. The results of experiments show that the terminal SO_3/SO_2 ratio in vapor clouds increases sharply as size of laser plume increases. This increase is caused by lowering the quenching temperature of SO_x redox reactions in the laser vapor clouds.Kinetic analysis of the above experimental results indicate that SO_3 formation rate found in our laser experiments is 100 to 3000 times the rate estimated based on extrapolation from literature data measured at much lower and higher temperatures than the temperature range in this study. This result suggests that there is a new reaction pathway to form SO_3 in a high-temperature vapor cloud, such as catalytic reaction on the surface of CaO. If such catalytic reaction exists, the conversion of SO2 to SO3 in the K/T impact is also much faster than previously thought. This will decrease the duration of sulfuric acid aerosol winter following the K/T impact and may enhance greatly the intensity of acid rain fall after the K/T impact.