Atmospheric Chemistry and Physics Discussions
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2006
10.5194/acpd-6-579-2006
http://www.atmos-chem-phys-discuss.net/6/579/2006/
http://www.atmos-chem-phys-discuss.net/6/579/2006/acpd-6-579-2006.html
http://www.atmos-chem-phys-discuss.net/6/579/2006/acpd-6-579-2006.pdf
579
613
2006-01-17
Kinetics and mechanism of heterogeneous oxidation of sulfur dioxide by ozone on surface of calcium carbonate
L. Li
Z. M. Chen
Y. H. Zhang
T. Zhu
J. L. Li
J. Ding
State Key Joint Laboratory of Environment Simulation and Pollution Control, College of Environmental Sciences, Peking University, Beijing 100871, China
Sulfate particles play a key role in the air quality and the global climate,
but the heterogeneous formation mechanism of sulfates on surfaces of
atmospheric particles is not well established. Carbonates, which act as a
reactive component in mineral dust due to their special chemical properties,
may contribute significantly to the sulfate formation by heterogeneous
processes. This paper presents a study on the oxidation of SO<sub>2</sub> by
O<sub>3</sub> on CaCO<sub>3</sub> particles. Using Diffuse Reflectance Infrared Fourier
Transform Spectroscopy (DRIFTS), the formation of sulfite and sulfate on the
surface was identified, and the roles of O<sub>3</sub> and water in oxidation
processes were determined. The results showed that in the presence of
O<sub>3</sub>, SO<sub>2</sub> can be oxidized to sulfate on the surface of CaCO<sub>3</sub>
particles. The reaction is first order in SO<sub>2</sub> and zero order in
O<sub>3</sub>. The reactive uptake coefficient for SO<sub>2</sub> oxidation by O<sub>3</sub>
was determined to be (1.4±0.3)×10<sup>−7</sup> using the BET area
as the reactive area and (7.7±1.6)×10<sup>−4</sup> using the
geometric area. A two-stage mechanism that involves adsorption of SO<sub>2</sub>
followed by O<sub>3</sub> oxidation is proposed and the adsorption of SO<sub>2</sub> on
the CaCO<sub>3</sub> surface is the rate-determining step. The proposed mechanism
can well explain the experiment results. The atmospheric implications were
explored based on a box model calculation. It was found that the
heterogeneous reaction might be an important pathway for sulfate formation
in the atmosphere.