Author : Heon Ho Lee
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)
Book Synopsis Development of a Coated-wall Flow Tube Reactor System to Investigate the Uptake Kinetics of Gaseous Elemental Mercury on Atmospherically-relevant Surfaces by : Heon Ho Lee
Download or read book Development of a Coated-wall Flow Tube Reactor System to Investigate the Uptake Kinetics of Gaseous Elemental Mercury on Atmospherically-relevant Surfaces written by Heon Ho Lee and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mercury (Hg) is a persistent, bioaccumulative and toxic pollutant that is cycled and dispersed globally throughout the environment. Its predominant form in the atmosphere is gaseous elemental Hg (Hg0(g)), and it is understood that the processes controlling the physicochemical conversion of Hg0(g) to gaseous oxidized Hg (GOM) and particulate-bound Hg (PBM) have significant implications to its fate and distribution throughout the environment.The atmospheric chemistry of Hg occurs through gas, aqueous and heterogeneous/interfacial reactions. Recent studies have shown that semiconductor oxides, which are present in the atmosphere as constituents of mineral dust, have the capacity to mediate the heterogeneous uptake and photocatalytic oxidation of Hg0(g). To date, however, just a few studies have systematically investigated the kinetics of these reactions at atmospherically relevant conditions or have considered their implications to the tropospheric cycling of Hg. To address these knowledge gaps, the objectives of this thesis were two parts: (1) first, to develop an experimental technique using the coated-wall flow tube reactor with cold vapor atomic fluorescence spectroscopy detection (CWFT-CVAFS), and (2) to use the CWFT-CVAFS system to measure the kinetic parameters (i.e., the uptake coefficients) of the uptake of Hg0(g) on a survey of semiconductor oxide surfaces (i.e., TiO2, Fe2O3 and Al2O3) and to determine the effects of radiation and relative humidity (RH) on the uptake kinetics. Consistent with previous reports from the literature, Hg0(g) uptake on the semiconductor oxides tested were highly dependent on light. Under visible and UV-A irradiation, Hg0(g) uptake on TiO2 was significantly limited by the mass transfer (i.e., gas phase diffusion) of Hg0(g) to the reactor walls, with uptake coefficients on the order of 10-4 and >10-3, respectively. With increasing relative humidity, the uptake coefficient of Hg0(g) on TiO2 decayed exponentially, with the uptake coefficient at 60% RH around 3 orders of magnitude smaller than under dry conditions. The uptake on Fe2O3 and Al2O3 were substantially slower than TiO2, which can be explained by the improved charge separation efficiency on TiO2 compared to Fe2O3, and the lack of band gap photoexcitation on Al2O3. Hg0(g) re-emission was induced on TiO2 and Al2O3 by the presence of water vapor under dark conditions (i.e., attributed to the displacement of physisorbed Hg0(ads)) and under UV irradiation (i.e., attributed to the photocatalytic reduction of chemisorbed HgO(ads)).The atmospheric implications were discussed under some simple approximations to investigate the conditions under which the heterogeneous uptake of Hg0(g) on mineral dust might be significant in the atmosphere. Based on the uptake coefficients measured in this report, it was found that under conditions with low %RH and high dust loading masses (>1000 μg m-3), the uptake of Hg0(g) on mineral dust could compete with gas phase processes"--
