Kinetic and mechanistic studies of the hydroxyl radical-initiated oxidation of reduced sulfides.

摘要

Atmospheric oxidation of DMS, although extensively studied in both field and laboratory, is an exceedingly complex process of which many steps remain uncertain. Accurate kinetic data and end product distributions, both as a function of temperature and pressure are required for atmospheric chemical models aimed at assessing sulfur-climate interactions. A pulsed laser photolysis - pulsed laser induced fluorescence system was employed to study the kinetics and mechanisms of the OH initiated oxidation of h₆-DMS. d₆-DMS, MES, DES, DPS and DBS between 100 Torr and 600 Torr of pressure and 240K–298K. Greatly improved technical capabilities of the PLP-PLIF system allowed for kinetics measurements under conditions of pressure and temperature approaching those encountered in the marine boundary layer. Key discrepancies in the DMS kinetic database were resolved and a predictive expression developed for OH initiated oxidation of DMS as a function of temperature and pressure. The expression predicts with high accuracy all data presented in this dissertation for h₆-DMS as well as prior datasets in the literature. The same system was also employed to study the OH initiated oxidation of MES, DES, DPS and DBS over the same range of temperature and pressure as for the DMS kinetic measurements. The current database for OH initiated oxidation of sulfides with C > 2 was extended and structure activity relationships were examined across the family of sulfides. This dissertation contains the first experimental evidence that OH initiated oxidation of the larger sulfides proceeds by an analogous, two-channel mechanism, to that proposed for DMS. This work has provided a robust and consistent image of OH initiated oxidation of reduced sulfides and a firm information base on which laboratory studies of subsequent oxidative steps can be based.