Impact of adsorbed nitrate on the heterogeneous conversion of SO2 on α-Fe2O3 in the absence and presence of simulated solar irradiation

Chengtian Du; Lingdong Kong; Assiya Zhanzakova; Songying Tong; Xin Yang; Lin Wang; Hongbo Fu; Tiantao Cheng; Jianmin Chen; Shicheng Zhang

doi:10.1016/j.scitotenv.2018.08.295

Impact of adsorbed nitrate on the heterogeneous conversion of SO₂ on α-Fe₂O₃ in the absence and presence of simulated solar irradiation

Sci Total Environ. 2019 Feb 1:649:1393-1402. doi: 10.1016/j.scitotenv.2018.08.295. Epub 2018 Aug 23.

Authors

Affiliations

¹ Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Institute of Atmospheric Sciences, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, China.
² Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Institute of Atmospheric Sciences, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, China; Shanghai Institute of Eco-Chongming (SIEC), No. 3663 Northern Zhongshan Road, Shanghai 200062, China. Electronic address: ldkong@fudan.edu.cn.
³ Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Institute of Atmospheric Sciences, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, China; Shanghai Institute of Eco-Chongming (SIEC), No. 3663 Northern Zhongshan Road, Shanghai 200062, China.
⁴ Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Institute of Atmospheric Sciences, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, China; Shanghai Institute of Eco-Chongming (SIEC), No. 3663 Northern Zhongshan Road, Shanghai 200062, China. Electronic address: jmchen@fudan.edu.cn.

PMID: 30308908
DOI: 10.1016/j.scitotenv.2018.08.295

Abstract

Adsorbed nitrate is ubiquitous in the atmosphere, and it can undergo photolysis to produce oxidizing active radicals. Nitrate photolysis may be coupled with the oxidation conversions of atmospheric gaseous pollutants. However, the processes involved remain poorly understood. In this study, the impact of adsorbed nitrate on the heterogeneous oxidation of SO₂ on α-Fe₂O₃ was investigated in the absence and presence of simulated solar irradiation by using in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that for α-Fe₂O₃ particles with no adsorbed nitrate, the formation of adsorbed sulfate on humid particles is stronger than that on dry particles. Meanwhile, light can also promote the heterogeneous conversion of SO₂ and the formation of sulfate on dry particles because α-Fe₂O₃ is a typical photocatalyst. However, the heterogeneous conversion of SO₂ on humid α-Fe₂O₃ particles is somewhat suppressed under light, suggesting the occurrence of photoinduced reductive dissolution. For the heterogeneous conversion of SO₂ on α-Fe₂O₃ particles with adsorbed nitrate, the formation of sulfate on humid particles is still higher than that on dry particles. For the dry α-Fe₂O₃ particles with adsorbed nitrate, light promotes the formation of adsorbed sulfate. For the humid α-Fe₂O₃ particles with adsorbed nitrate, the heterogeneous conversion of SO₂ under light is stronger than that under no light, indicating that the photolysis of adsorbed nitrate is coupled with the oxidation of SO₂ and the formation of sulfate. The consumption of adsorbed nitrate and the formation of adsorbed N₂O₄ are observed during the introduction of SO₂. A possible mechanism for the impact of adsorbed nitrate on the heterogeneous conversion of SO₂ on α-Fe₂O₃ particles is proposed, and atmospheric implications based on these results are discussed.

Keywords: Adsorbed nitrate; Heterogeneous reaction; Nitrogen dioxide; Photolysis; Simulated solar irradiation; Sulfur dioxide.