Studies of ozone initiated reactions of gaseous mercury: kinetics, product studies, and atmospheric implications

Abstract

Kinetics of O₃ initiated oxidation reaction of Hg⁰ was performed in N₂ and over the temperature range of 283–323 K at pressure of 750 ± 1 Torr, in order to provide further understanding of geochemical mercury cycling. Kinetic studies were carried out using relative and absolute techniques by gas chromatography with mass spectroscopy (GC-MS). The room temperature reaction rate constant was determined to be (7.5 ± 0.9) × 10⁻¹⁹ cm³ molecule⁻¹ s⁻¹. The calculated activation energy (E_A) and pre-exponential factor (A) were 11.7 ± 0.27 kJ mol⁻¹ and 8.43 × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹, respectively. For the first time, products of O₃-initiated oxidation of elemental mercury have been studied in the gas-phase, from the suspended aerosols, and from the wall of the reactor, using chemical ionization mass spectrometry (CI-MS), GC-MS, and inductively coupled plasma mass spectrometry (ICP-MS). Under our experimental conditions, the dominant identified product was HgO, which was mainly adsorbed on the reaction walls, and there was less than 1% of the reaction product collected on the micron filters (0.5 μ) from the suspended aerosols. The implications of our kinetics and product studies to the chemistry of the atmosphere are herein discussed.