28 Oct 2021

28 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Aqueous chemical bleaching of 4-nitrophenol brown carbon by hydroxyl radicals; products, mechanism and light absorptivity

Bartłomiej Witkowski, Priyanka Jain, and Tomasz Gierczak Bartłomiej Witkowski et al.
  • University of Warsaw, Faculty of Chemistry, al. Żwirki i Wigury 101, 02-089 Warsaw, Poland

Abstract. The reaction of hydroxyl radicals (OH) with 4-nitrophenol (4-NP) in the aqueous solution was investigated at pH = 2 and 9. As a result, the molar yield of the phenolic products was measured to be 0.20 ± 0.05 at pH = 2 and 0.40 ± 0.1 at pH = 9. The yield of 4-nitrocatechol (4-NC) was higher at pH = 9; at the same time, a lower number of phenolic products was observed due to the hydrolysis and other irreversible reactions at pH > 7. Mineralization investigated with total organic carbon (TOC) technique showed that after 4-NP was completely consumed approx. 85 % of the organic carbon remained in the aqueous solution. Hence, up to 65 % of the organic carbon that remained in the aqueous solution accounted for the open-ring non-phenolic products.

The light absorptivity of the reaction solution between 250 and 600 nm decreased as a result of OH reaction with 4-NP. At the same time, 4-NP solution showed some resistance to chemical bleaching due to the formation of the light-absorbing by-products. This phenomenon effectively prolongs the time-scale of chemical bleaching or 4-NP via reaction with OH by a factor of 3–1.5 at pH 2 and 9, respectively. The experimental data acquired indicated that both photolysis and reaction with OH can be important removal processes of the atmospheric brown-carbon from the aqueous particles containing 4-NP.

Bartłomiej Witkowski et al.

Status: open (until 09 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Bartłomiej Witkowski et al.

Bartłomiej Witkowski et al.


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Short summary
This article describes a thorough investigation of the chemical reaction of 4-nitrophenol (4-NP) with hydroxyl radicals (OH) carried out in the laboratory aqueous photoreactor. We report the formation of key intermediates under different pH conditions and the evolution of the light absorptivity of the reaction solution. The results provided new insights into the formation and removal (chemical bleaching) of light-absorbing organic aerosols (atmospheric brown carbon).