27 Jan 2022
27 Jan 2022
Status: this preprint is currently under review for the journal ACP.

The Positive Effect of Formaldehyde on the Photocatalytic Renoxification of Nitrate on TiO2 Particles

Yuhan Liu, Xuejiao Wang, Mengshuang Sheng, Chunxiang Ye, and Jing Shang Yuhan Liu et al.
  • State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, 5 Yiheyuan Road, Beijing 100871, P. R. China

Abstract. Renoxification is the recycling of NO3/HNO3 into NOx under illumination; it is promoted by the photocatalysis of TiO2. Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, may participate in the renoxification of nitrate-doped TiO2 (NO3-TiO2) aerosols. In this study, we established an environmental chamber reaction system under different light sources, excluding direct photolysis of nitrate by adjusting the illumination wavelength, to explore the photocatalytic renoxification process. It is suggested that HCHO and TiO2 have a significant synergistic effect on photocatalytic renoxification via the NO3-NO3•-HCHO-HNO3-NOx pathway. Adsorbed HCHO may react with nitrate radicals through hydrogen abstraction to form HNO3 on the surface, resulting in the mass generation of NOx. We found that for 4 wt% NO3-TiO2 aerosols (e.g., KNO3-TiO2), the NOx concentration reached up to 110 ppb, and was 2 orders of magnitude higher than in the absence of HCHO. Nitrate type and contents, relative humidity, and HCHO concentration were found to influence NOx release. The significant synergistic enhancement effect of renoxification affects photochemical processes such as atmospheric oxidation and nitrogen cycling on the surfaces of particles containing semiconductor oxides, with the participation of hydrogen donor organics.

Yuhan Liu et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-6', Anonymous Referee #1, 14 Feb 2022
    • AC1: 'Reply on RC1', Jing Shang, 23 Mar 2022
  • RC2: 'Comment on acp-2022-6', Anonymous Referee #2, 02 Mar 2022
    • AC2: 'Reply on RC2', Jing Shang, 23 Mar 2022
  • RC3: 'Comment on acp-2022-6', Anonymous Referee #3, 16 Mar 2022
    • AC3: 'Reply on RC3', Jing Shang, 23 Mar 2022

Yuhan Liu et al.

Yuhan Liu et al.


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Short summary
NOx plays an important role in the formation of secondary aerosols and atmospheric oxidants. Formaldehyde, a typical organic component found in atmosphere, was found to enhance NOx release from nitrate particles containing photocatalytic TiO2 under illumination. A chamber experiment was designed to exclude the direct photolysis of nitrate while make the photocatalytic process dominant. The results would be benefit to the understanding of atmospheric nitrogen cycling and verification of models.